JP2825383B2 - Improved anode for oxygen generation - Google Patents

Abstract

A metal surface is now described having enhanced adhesion of subsequently applied coatings. The substrate metal of the article, such as a valve metal as represented by titanium, is provided with a highly desirable surface characteristic for subsequent coating application. This can be achieved by a plasma sprayed coating of well defined surface morphology, the plasma spraying being with one or more metals usually valve metals. The metal of the coating may be the same or different from the metal of the substrate. Subsequently applied coatings, by penetrating into the coating of well defined surface morphology, and desirably locked onto the resulting metal article an provide enhanced lifetime even in rugged commercial environments.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a valve metal.
A used electrode material whose part of the surface is cut off during use and loses smoothness, and a valve whose surface is flattened by plasma spraying and has a desired surface roughness to enhance coating adhesion. The present invention relates to an anode for oxygen generation having a plasma sprayed coating layer made of a metal and an electrochemically active surface coating layer containing a platinum group metal or an oxide thereof on the surface thereof.

[0002]

BACKGROUND OF THE INVENTION The adhesion of coatings applied directly to electrode substrate metal surfaces is particularly critical when the coated metal is used in harsh industrial environments. Usually, the surface treatment and pre-treatment operations before coating are performed carefully. In such treatment or pre-treatment operations, it is most important to have a clean surface.

A typical example of a coating applied directly to an electrode substrate is an electrocatalytic coating, which frequently contains a platinum group noble metal, and is applied directly on a metal such as a valve metal. In the field of electrocatalyst coating applied to electrode substrates, metals are simply washed to a very smooth surface (US Pat. No. 4,7,738).
97,182). Fluorine compound treatment smoothes the surface (US Pat. No. 3,864,163).
Cleaning includes chemical degreasing, electrolytic degreasing or treatment with an oxidizing acid (US Pat. No. 3,864,163). The surface for coating is prepared by mechanical roughening after washing (US Pat. No. 3,778,307). If the mechanical treatment is a sandblasting treatment, it is then etched (US Pat. No. 3,878,083). Alternatively, a fine-grained mixture of metal powders may then be applied by flame spraying (US Pat. No. 4,849,085).

[0004] An alternative to fixing the new coating to the electrode substrate is to form a layer of porous oxide on the electrode substrate, which is used when applying an electrocatalytic coating to the valve metal. It has been found to be useful. For example, as disclosed in U.S. Pat. No. 4,140,813,
The active substance can be applied electrochemically after flame or plasma spraying of titanium oxide on the electrode substrate metal. Alternatively, as taught in U.S. Pat. No. 4,392,927, the thermal spray material pre-coated with active particles as an electrocatalyst may be a metal oxide, nitride, or the like.

However, it is difficult to provide a long-life coated electrode for use in the most demanding commercial environments such as the oxygen generating anodes currently used commercially in electroplating, electrotinning, electroforming or electrowinning. is there. The above operation is a continuous operation and involves severe conditions including possible surface damage. It would be most desirable if such a procedure could provide a coated metal substrate as an electrode that could be operated stably for a long period of time while maintaining excellent bonding of the coating. It would also be highly desirable to be able to provide such electrodes not only from new metals, but also from recoated metals.

[0006]

SUMMARY OF THE INVENTION Locked on coating, which is now an excellent coating adhesive
The metal surface giving g) was found. Such coated electrode substrates can have a very desirable long life even in the harshest industrial environments. ADVANTAGE OF THE INVENTION According to this invention, a part of the surface is cut off at the time of use, and it is possible to apply a sufficiently fixed coating having uniform flatness to the surface of the used electrode material which has lost its smoothness.

The present invention relates to an electrode having an electrode substrate surface having a surface roughness suitable for enhancing the coating adhesiveness, wherein said surface is a valve metal surface coated by plasma spraying on said substrate. And the plasma sprayed surface is
Average surface roughness greater than or equal to about 6.4 μm (250 microinches) as measured by a profilometer and an upper profile meter threshold of 10.2.
It has an average of about 15.7 (40 / inch) or more surface peaks per centimeter, based on μm (400 microinches) and the lower threshold of the profilometer 7.6 μm. The above profile meter is a commercially available surface roughness measuring device. In the structure, when the probe arm crosses the surface, a current proportional to the surface roughness is induced, and the surface roughness can be measured. The surface roughness is determined based on the measurement of the profile meter by the average plane roughness (Ra), the average surface peak (Nr), and the average distance (R) between the maximum peak and the maximum valley.
m) and the average peak height (Rz). In order to obtain the average surface peak number (Nr), the number of peaks per centimeter (Nr) is measured with reference to variable upper and lower reference values (upper threshold value and lower threshold value) that are variable for the cross-sectional curve. I do.

The present invention is a method of arranging a plasma metal surface to enhance coating adhesion on a surface that has been cut out and loses planarity during use, the method comprising providing a valve on the cut-out portion of such a surface. The metal is plasma-sprayed to establish the flatness of the metal surface, and then plasma-sprayed to form the desired surface roughness and enhance the coating adhesion.

The anode for oxygen generation according to the present invention is highly desirable even under severe commercial operations including continuous electrogalvanizing, electrotinning, copper foil plating, electroforming or electrowinning and sodium sulfate electrolysis. It can have a working life.

[0010]

The electrode base material is always titanium,
Valve metals including tantalum, aluminum, zirconium and niobium are used. Of particular interest in terms of roughness, corrosion resistance and availability is titanium. Metals suitable as a substrate, in addition to the commonly available elemental metals,
Alloys and intermetallics containing one or more valve metals as well as ceramics and cermets are included. For example, titanium can be an alloy of nickel, cobalt, iron, manganese or copper. More specifically, grade 5
Titanium contains up to 6.75% by weight of aluminum and 4.5% by weight of vanadium, Grade 6 titanium contains up to 6% of aluminum and 3% tin, Grade 7 titanium contains up to 0.25% by weight of palladium Grade 10
Titanium is 10-13% molybdenum and 4.5-7.
Containing 5% by weight of zirconium and so on.

The use of elemental metals, alloys and intermetallic mixtures means, in particular, the use of metals of generally available conditions, ie metals containing small amounts of impurities. That is, for titanium, which is a metal of particular interest, various grades are available, including those whose other components are alloys or alloy plus impurities. Titanium grades are further described in the ASTM B265-79 standard specification for titanium.

Regardless of the choice of metal for the electrode substrate and the subsequent treatment of the metal surface, it is advantageous for the surface of the electrode substrate metal to be clean. This can be achieved by any process that cleans the metal surface of the electrode substrate, but if removal of old coatings is not necessary or if etching is used, as described in detail below. Usually, mechanical cleaning is minimized. That is, a conventional cleaning method by chemical degreasing or electrolytic degreasing, or other chemical cleaning operations can be advantageously used.

If there is an old coating on the metal surface of the electrode substrate, it is necessary to check whether the above-mentioned cleaning is necessary before recoating. For maximum performance when using the anode for oxygen generation according to the present invention, it is preferable to remove the old coating. Chemical means of coating removal are well known in the art of the present invention for electrochemically active coatings on valve metal. That is, US Pat.
Pickling immediately after treatment with a melt of an essentially basic material, as taught in U.S. Pat. No. 73,100, suitably reconstructs the metal surface. Also, as described in U.S. Pat. No. 3,706,600, it is useful to treat with a melt of an alkali metal hydroxide containing an alkali metal hydride and then with a mineral acid. . Normal rinsing and drying steps can also form part of these operations.

In the practice of the present invention, if the electrocatalytic coating is applied to the valve metal after the surface has been cleaned or after the surface has been prepared and cleaned, the surface becomes rough. This is achieved by means of plasma spray coating, usually using finely divided valve metals, especially titanium powder. However, as described below, although the metal is applied in finely divided form, the supply metal, that is, the metal to be applied, may be in another form, such as a wire form. It should be understood that the reason why the application of the fine metal particles is described as a typical application method is for convenience. In this plasma spraying method, the metal is melted, and an inert gas containing a small amount of hydrogen as an optional component, such as argon or nitrogen, is heated to a high temperature by an electric arc, and the molten metal is sprinkled in the plasma flow generated thereby. is there. The term "plasma spraying" as used in the present invention, although plasma spraying is preferred, should generally be understood to also include thermal spraying, such as magnetohydrodynamic spraying, flame spraying and arc spraying. Must.

The spray parameters, such as the volume and temperature of the flame or plasma spray stream, the feed rate of the fine metal component, etc., may vary depending on the form in which the fine metal component is melted and substantially molten in the spray stream. It is selected so as to deposit on the substrate metal as it is, and thus have an essentially continuous coating having a perforated structure (ie, a coating in which the sprayed particles are indistinguishable). Typically, spray parameters as used in the examples provide satisfactory coatings. Usually, the base metal during melt spraying is maintained at a temperature close to room temperature. this is,
This is achieved by means such as applying an air flow onto the substrate during thermal spraying, or air cooling the substrate between thermal spray passes.

The typical particle size range of the finely divided metal used, for example titanium powder, is 20-100 microns, with all particles preferably in the range of 40-80 microns for efficient surface roughening. . Metal particles having different particle sizes are equally suitable as long as they are easily plasma sprayed. The composition of the particulate metal is similar to that described above for the base metal, for example titanium is one of several grades, usually grade 1 titanium. It is also conceivable to apply a mixture, for example a mixture of metals or a mixture of metals and other components. Other components include metal oxides.
In the mixture of the metal and the other component, for example, the metal is the majority and the other component is the non-half. It is also conceivable to use such plasma spray coating in combination with etching of the base metal surface. The respective treatments are almost always applied to different parts of the surface. When using etching, the metal surface is violently etched to deepen grain boundaries,
It is important that the three-dimensional crystal grains are sufficiently exposed. It is preferable that impurities near the grain boundaries be etched by such an operation. Especially old coatings are present,
If the coated substrate is used, for example, as an electroplating anode, the metal product will lose its shape,
Surface flatness may be lost. Typically, such shape defects will be surface defects or cut-outs. For the sake of convenience, surface irregularities including defects, scratches and perforated portions, and burns where the metal actually melts and re-solidifies are referred to in the present invention as perforated portions. These excavated parts may or may not be filled with metal. If the entire surface is subsequently etched before recoating, it is expected that the etching effect in the filled area may be poor. Also, the cut-out portions of the substrate may be stretched or the substrate may be subject to thermal history and / or chemical action that will not produce the desired results for etching. It is therefore particularly desirable to simply plasma spray the entire surface, so that these substrate defects can be overcome. In some cases, a combination of plasma spraying and etching may be useful. That is, the excavated portion is filled with the plasma spraying technique. Usually, the non-deformed surface area is first etched, and then the flat etched surface is masked, and the remaining undercut is filled and / or surface treated by plasma spraying. . That is, plasma spraying can be used to fill and re-activate the excavated area, or simply to re-activate the excavated area without necessarily restoring the planarity of the surface. Can also be used. Reactivation means a plasma spray application which then prepares the cutout for processing. In this way, the entire surface has the roughness required for coating. If desired, it may be re-polished to the desired flatness during this same process.

When using etching, the heat treatment history of the metal can be important. For example, in preparation for etching a metal such as titanium, it is most useful to adjust the condition of diffusing impurities to the grain boundaries by annealing or the like. For example, properly annealing grade 1 titanium increases the concentration of iron impurities at grain boundaries. If the preferred adjustment is annealing and the metal is grade 1 titanium, the titanium can be annealed at a temperature of about 500 ° C. or more for a time of about 15 minutes or more. Higher annealing temperatures, e.g., 600-800 <0> C, are advantageous in terms of operating efficiency.

If etching is used, it is performed with a sufficiently active etching solution that violently attacks the grain boundaries. A typical etching solution is an acidic solution, which may be hydrochloric acid, sulfuric acid, perchloric acid, sulfuric acid, oxalic acid, tartaric acid and phosphoric acid and mixtures thereof, such as aqua regia. Other etchants that can be used include caustic etchants, such as a mixed solution of potassium hydroxide / hydrogen peroxide or a melt of potassium hydroxide and potassium nitrate. In terms of operating efficiency, it is advantageous if the etching solution is a strong or concentrated solution, for example a 18-22% by weight hydrochloric acid solution. Furthermore, this solution may be used in the case of an aqueous solution at the time of etching.
It is advantageous if the temperature is maintained at an elevated temperature of not less than 0 ° C., and the temperature is frequently maintained at or near the boiling condition or at a higher temperature, for example, a reflux state. After etching, the etched metal surface can be subjected to a rinsing and drying step to prepare the surface for coating. For a more detailed description of etching and annealing, see U.S. Pat.
No. 4,429, the disclosure of which is cited.

Regarding the plasma sprayed surface roughness, the metal surface has an average roughness (Ra) of about 6.4 μm (250 microinches) or more and an average of about 15.7 (40 / cm) per centimeter. Inches) or more. The number of surface peaks per centimeter is typically lower than 7.6 μm (30 μm).
0 microinches) and an upper threshold of 10.2 μm (400
Microinches).
Surfaces having an average roughness of less than about 6.4 μm (250 microinches) are undesirably smooth for the substantial enhancement of required coating adhesion, with an average of less than about 15.7 surfaces per centimeter. The same applies to a surface having a peak. About 10.2 μm (400 micro inches) or more,
For example, about 19.1 to 38.1 μm (750-1500
Micron inches) and have an average roughness in the range of about
Surfaces that do not contain low spots of less than 1 μm (200 microinches) are advantageous. To avoid surface smoothing, it is necessary to use about 5.3 to 5.6 μm (210 to 220 μm).
Advantageously, the surface does not contain low spots of less than microinches. About 7.6 to about 12.7 μm
Surfaces having a surface roughness of (300 to 500 microinches) are preferred. Advantageously, the average number of peaks per centimeter of the surface is about 23.6 (60 / inch) or more, and about 51.1 (130 / inch).
The average may be about 31.4 to about 47.2.
It is preferably 80/120 pieces / cm. The average distance (Rm) between the maximum peak and the maximum valley is about 25.4 μm (1000 micro inches)
And the average peak height (Rz) is about 25.
Surfaces that are 4 μm (1000 microinches) are even more advantageous. All of the above surface properties are measured with a profilometer. Rm value of about 38.1 to 88.9 μm
(1500 to 3500 microinches) and more desirably a coating surface having a maximum valley characteristic of about 38.1 to 88.9 μm (1500 to 3500 microinches).

After the substrate has reached the required surface roughness, the surface is subjected to various operations including pretreatment before being coated. For example, the surface is subjected to a cleaning operation such as solvent cleaning. Alternatively, it is subjected to the next etching, hydrogenation treatment or nitridation treatment. Prior to coating with the electrochemically active material, the oxide layer may be heated or anodized in air as described in U.S. Pat. No. 3,234,110. It has been proposed to provide European Patent Application No. 0,090,42
No. 5 proposes electroplating platinum on a substrate, followed by chemical deposition of ruthenium, palladium or iridium oxide on it. Various proposals have also been made for depositing an outer layer of an electrochemically active material on a lower layer which mainly serves as a protective intermediate and a conductive intermediate. GB 1,344,540 discloses the use of an electrodeposited layer of cobalt or lead oxide under a ruthenium-titanium oxide or similar active outer layer. U.S. Pat. Nos. 4,272,354 and 3,882,00
No. 2 and 3,950,240,
Various tin oxide based underlayers are disclosed.

The coatings that the present invention most considers after applying any necessary surface roughness and any pre-treatment are electrochemically active coatings, typically platinum or other platinum group metals. And they can be referred to as active oxide coatings, such as coatings of platinum group metal oxides, magnetite, ferrite, cobalt spinel or mixed metal oxides. Such coatings have typically been developed for anode coatings in the electrochemical industry. These are coated with water or, for example, an alcoholic solvent. A preferred coating of this type is disclosed in U.S. Pat. No. 3,265,5.
No. 26, 3,632,498, 3,711,385 and 4,528,08
No. 4, generally described. Mixed metal oxide coatings frequently include one or more oxides of the platinum group metals, including platinum, palladium, rhodium, iridium and ruthenium or mixtures thereof, and valve metal oxides including other metals. Further coatings in addition to those listed above include manganese dioxide, lead dioxide, MxPt ₃
O ₄ (M is an alkali metal and x is typically about 0.
Platinate coatings such as
There are nickel oxide and nickel-lanthanide oxide.

It is contemplated that the coating is applied to the metal by any means useful for applying the liquid coating composition to a metal substrate. Such methods include a dip spin method and a dip drain method.
In) method, brush coating method, roll coating method, and spray coating method such as electrostatic spraying. Furthermore, a combination technique with a spray coating method, for example, a combination of a dipping / draining method and a spray coating method can also be used. For those coating compositions that provide an electrochemically active coating, dipping and drainage modification methods are most useful. After any of the above coating operations, the coating is removed from the liquid coating composition and the coated metal surface is immersed and drained or subjected to other treatments such as forced air drying.

Typical curing conditions for the electrocatalyst coating are a curing temperature of about 300 to about 600 ° C. The curing time varies for each coating layer and varies from just a few minutes to over one hour. For example, when several coating layers are applied, the curing time becomes longer. However, curing operations that overlap with annealing conditions at elevated temperatures and prolonged exposure to such elevated temperatures are generally avoided from an economic standpoint. Generally, the curing technique used can be any that can be used to cure a coating on a metal substrate. That is, oven curing including a conveyor oven can be used. Furthermore,
Infrared curing technology can also be used. For most economical curing, the use of oven curing is preferred, and curing temperatures used for electrocatalytic coating are from about 450 to about 55.
Within the range of 0 ° C. At such temperatures, the curing time of each applied coating is almost always only a few minutes, for example 3 to 10 minutes. The following examples illustrate the practice of the present invention and comparative examples. However,
This example, which illustrates how to practice the invention, should not be construed as limiting the invention.

[0024]

REFERENCE EXAMPLE 1 A titanium nut was welded to the back of each sample plate made of unalloyed grade 1 titanium and having a sample surface of about 7.5 cm ² . Next, the sample plate was placed on a large backing sheet metal, and the sample plates were arranged in a mosaic shape. This loading array functioned as a large sample plate array that could be handled as one unit in the following operations. This sample plate was subjected to grit blasting with aluminum oxide, and then rinsed with acetone and dried.

A coating of titanium powder was formed on a sample plate using titanium powder having an average particle size of 50-60 microns. GH
A sample plate was coated with this powder using a Metoco plasma spray gun equipped with a spray nozzle. Thermal spraying conditions are: 500 ampere current; voltage 45-50 volts;
Plasma gas argon and helium; titanium supply rate 1
The spray bandwidth was 6.7 millimeters; and the spray distance was 64 mm. The resulting titanium layer on the titanium sample plate was approximately 150 microns thick.

Next, the coated surface of the sample plate was subjected to a surface profilometer measurement using a Hommel model T1000C apparatus manufactured by Hommelwerk GmbH. The sample plate surface profilometer measurements were determined by calculating the average from three separate measurements made by running the instrument in a random orientation across the coated flat surface of the sample plate. As a result, the average values of the surface roughness (Ra) measured for the three samples were 11.4, 12.4 and 13.9 μm (448, 490 and 548 microinches), respectively, and the number of peaks / cm (Nr) was The values for the three sample plates were 29.9, 24.8 and 29.9 (76.63 and 76 pieces / inch), respectively. The number of peaks per centimeter was measured within the threshold limits of 7.6 μm (300 microinches, lower limit) and 10.2 μm (400 microinches, upper limit).

[0027]

EXAMPLE 1 A surface of an electrode substrate, which was previously coated with an electrochemically active coating and which had lost its smoothness because the surface was cut off with a used sample, was blasted with alumina powder. To remove the previous coating. The removal of the previous coating by this polishing method was measured by fluorescent X-rays. After removing the residue of the polishing treatment, the obtained sample plate was subjected to an etching treatment. When it was immersed in a 20% by weight aqueous hydrochloric acid solution heated to 95 ° C. for about 1 hour, it was etched away.
After removing the sample plate from the hot hydrochloric acid, it was rinsed again with deionized water and air-dried. According to the profile meter measurement performed by the method of Reference Example 1, the average value on the flat surface of the sample was Ra 4.6 μm (180 micro inches) and Nr
12.2 pieces / cm (31 pieces / inch).

Next, using the titanium powder and the coating method described in Reference Example 1, the sample was coated with plasma sprayed titanium. According to the profilometer measurement performed by the method of Reference Example 1, the average value on the flat surface of the sample was Ra16.5 μm.
m (650 micro inches) and Nr 27.2 pcs / cm
(69 pieces / inch).

────────────────────────────────────────────────── ⁶ Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI C25D 17/10 101 C25D 17/10 101A (72) Inventor Richard Sea Carlson 44123, Ohio, USA United States of America, East Tohand Red Sixties Street 51 (72) Inventor Kenneth El Hardy 15818 Georgia Road, Middlefield 44062, Ohio, United States 1556 (56) References JP-A-59-50195 (JPA) Field (Int.Cl. ⁶ , DB name) C25D 17/10-17 / 12,1 / 04 C25B 11/10 C25C 7/02

Claims (3)

(57) [Claims] 1. An electrochemically active surface coating layer containing a platinum group metal or an oxide thereof, selected from the group consisting of titanium, tantalum, niobium, zirconium, alloys and intermetallic compounds. A part of the surface is cut off during use, and the used electrode material which has lost smoothness, and the surface of the electrode material which has lost smoothness, has enhanced coating adhesion. A valve metal containing at least one selected from the group consisting of titanium, tantalum, niobium, zirconium, alloys and intermetallic compounds thereof, which has been flattened and surface-roughened by plasma spraying. A plasma spray coating layer, and an electrochemically active surface containing a platinum group metal or an oxide thereof coated on the surface of the plasma spray coating layer Becomes more and covering layer, wherein the plasma spray coating the coating layer is 6.4μm as measured by profilometer (250 microinches) or more the average surface roughness and profilometer upper threshold 10.2μm
(400 micro inches) and the lower limit threshold of the profile meter 7.6 μm (300 micro inches)
Oxygen having an average surface peak of not less than 15.7 (40 / inch) per centimeter, and the particle size of the valve metal of the plasma sprayed coating is 20-100 microns. Anode for generation. 2. The electrode according to claim 1, wherein said electrode is an anode of an anodizing tank, an electroplating tank, or an electrowinning tank. 3. The electrode according to claim 1, wherein said electrode is an anode of electrogalvanization, electrotin plating, sodium sulfate electrolysis or copper foil plating.