US20030010649A1

US20030010649A1 - Inert anode for electrochemical process

Info

Publication number: US20030010649A1
Application number: US09/906,364
Authority: US
Inventors: Michael Waite; E. Horonzy
Original assignee: Eltech Systems Corp
Current assignee: Eltech Systems Corp
Priority date: 2001-07-16
Filing date: 2001-07-16
Publication date: 2003-01-16
Also published as: WO2003008669A1

Abstract

An anode structure suitable for an electrochemical process is disclosed. The anode comprises a primary anode structure, also referred to as an anode frame, and a secondary metal substrate attached to the anode frame. The anode frame is a structural support and suitable electrical conductor. The metal substrate has an electrocatalytic coating and provides the anode with an anodic surface. The metal substrate is easily removable from the anode frame. Also disclosed is a method for refurbishing anodes according to the present invention. An anode comprising an anode frame and a metal substrate is refurbished by removing a depleted metal substrate from the frame and attaching a separate precoated metal substrate to the frame. The method of refurbishing optionally includes refurbishing the depleted metal substrate and using the refurbished substrate to refurbish the anode structure. A method for providing replacement anodes is also disclosed. The method includes supplying a user with an anode comprising an anode frame and a metal substrate attached thereto. The method also includes supplying one or more additional pre-coated substrates to the user, such that the user may refurbish the anode when necessary.

Description

BACKGROUND OF THE INVENTION

Conventional anodes utilized in aqueous electrochemical processes consist of a single manufactured article designed to (1) accommodate passage of electrical current and (2) provide the necessary amount of electrochemically active surface area to serve a corresponding cathode. Conventional anodes are constructed of materials that provide suitable structural properties and the desired chemical and electrical properties necessary for the process. Additionally, conventional anodes used in most applications must be treated with an electrocatalytic surface such as a ceramic electrocatalyst, or platinum metal, or a platinized niobium mesh. The anodic surface material is therefore an integral part of the manufactured article. Treatment or coating of the critical anodic surfaces allows electrochemical reactions to proceed at the surface of the anode. In aggressive electrochemical applications, the anodic surface must also have the property of being resistant to corrosion or dissolving. In order to assure proper distribution of electrical current to all areas of the cathode, conventional anodes often exhibit complicated geometric configurations mated to the geometry of a cathode. Such requirements often result in large anodes having elaborately shaped anodes.

Many disadvantages associated with conventional anodes involve the process of applying or replacing the anodic surface. Preparation of the anodic surface requires that the critical anodic surface of the anode be altered by attachment of an electrochemically active material. Possible methods of altering the anode surface include thermal decomposition of a chemical paint to form a ceramic coating, or plating with a noble metal such as platinum, or attaching another suitable anode material to the surface such as platinum foil or a composite comprised of platinum and niobium metal, or some other method for applying an electrochemically active surface. Conventional anode preparation requires the entire anode structure to be processed, even if only a small portion of the anode surface is used as an active anode surface.

In the case of ceramic coatings, the surface is prepared by firing the anode in a furnace after each application of a chemical paint. Multiple applications and firings are required to form a coating of acceptable thickness and durability. It is necessary, with conventional methods to handle and fire the entire anode in order to obtain an acceptable coating on that portion of the anode which comprises the electrochemically active area. The application of a ceramic anode coating to a large or complex shaped anode is often a difficult, laborious process. Large anodes of complex shapes may occupy a significant volume of the furnace and reduce the space available to treat the actual anodic surface area. In some cases, commercial anodes are too large for typical industrial furnace.

In a similar manner, platinized anodes and anodes having a surface comprised of platinum/niobium composites require handling of the entire anode structure in order to obtain an acceptable coating in the electrochemically active area. Another disadvantage associated with conventional anodes is that repeated handling of the entire anode structure increases the potential that the anode may be damaged during application of the anodic surface. Additionally, surface preparation treatments such as grit blasting, sanding, degreasing, etching, etc., may be performed on the entire anode prior to application of the anodic surface. Consequently, the processing of conventional anodes is often time consuming, labor intensive, and expensive.

After an anodes has been in service, the anodic surface becomes worn or electrolytically inactive and must be replaced. Conventional anodes are refurbished by applying a fresh electrolytically active anodic surface to an anode that is depleted or worn away. Since the entire anodic surface must be replaced, conventional anodes requires subjecting an anode having an inactive surface to the above cumbersome, timely, and expensive surfacing process. Additionally, refurbishing could result in lost production for the user, since operation of the electrochemical process cannot be performed while an anode is being refurbished. Users of industrial anodes often must maintain a supply of spare anodes so that production is not interrupted while worn anodes are being refurbished.

It is therefore desirable to provide an anode that exhibits a satisfactory anodic surface area, provides the desired geometry, provides good electrical conductivity, and is easier and less expensive to process than conventional anodes. It is also desirable to provide an anode that is quickly and easily refurbished. It is further desirable to provide an anode that may be refurbished by the end user thereby avoiding the need for sending the anode out to be refurbished.

SUMMARY OF THE INVENTION

The present invention addresses many of the disadvantages associated with conventional anodes and provides, in a first aspect, an anode for an aqueous electrochemical process comprising an anode frame and a separate removable mesh or sheet substrate attached to the anode frame. The anode frame provides the anode with proper electrical conduction and proper geometry. The removable substrate includes an electrocatalytic coating and provides an anodic surface. Moreover, the present invention provides a two-part anode system comprising a frame structure and a removable substrate that is treated with a suitable anodic surface.

In another aspect, the present invention provides a method for refurbishing an anode comprising the steps of 1) providing an anode comprising an anode frame and a removable metal substrate attached thereto, wherein the metal substrate includes an electrocatalytic coating; 2) employing the anode of step 1 in an electrochemical process and depleting the electrocatalytic coating from the metal substrate; 3) removing the metal substrate from the anode frame; 4) applying an electrocatalytic coating to a second metal substrate; 5) attaching the metal substrate of step 4 to the anode frame of step 3; and 6) employing the anode of step 5 in an electrochemical process. While the anode frame could include an anodic coating, the present invention typically avoid such a coating, rendering the frame reusable without (or with minimal) refurbishment, i.e., only the spent anode is removed and a fresh anode is reattached.

In a further aspect, the present invention provides a method for providing replacement anodes for electrochemical processing. The method includes supplying an anode to a user, wherein the anode comprises an anode frame and a metal substrate having an electrocatalytic coating attached to the anode frame. The method also includes supplying one or more additional metal substrates having an electrocatalytic coating to the user. The user depletes the electrocatalytic coating from the metal substrate during an electrochemical process, then removes the metal substrate from the anode frame after the process. The user refurbishes the anode by attaching one or more additional metal substrates to the anode frame. The user repeats the above process as necessary.

An advantage of the present invention is that it provides a simplified anode design compared to conventional anodes and still provides the desired geometry and anodic surface area.

Another advantage of the present invention is that it provides easier processing of critical anodic areas compared to conventional anodes.

Still another advantage of the present invention is that it utilizes less anodic material but provides comparable or larger critical anodic surface areas compared to conventional anodes.

Yet another advantage to the present invention is that it reduces damage to the frame and/or the anode resulting from oxidation and/or repeated handling through processing.

A further advantage of the present invention is that it provides an anode that is easily and quickly refurbished.

Another advantage of the present invention is that it allows the end user to refurbish anodes thereby eliminating the disruption of sending the anode out for refurbishing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of an anode comprising a metal substrate attached to an anode frame.[0016]
The figures are merely illustrative of the invention and its embodiments. Specifically, the figures are for illustrative purposes and not to be construed as limiting the present invention. [0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Anodes [0018]
With reference to FIG. 1, an [0019] anode 10 comprises a primary anode structure 12 and a secondary substrate 14 attached to the primary anode structure. Primary anode structure 12 is a frame. Metal substrate 14 is an expanded metal mesh and provides the anodic surface of anode 10. Metal substrate 14 is attached to primary anode structure 12 by welding, clamping, or some other method of attachment which provides good electrical connection.
[0020] Anode 10 is employed as an anode in an electrochemical process and distributes electrical current to a corresponding cathode (not shown). Primary anode structure 12 is connected to an electrical source (not shown). Primary anode structure 12 serves to conduct electrical current from the source to the secondary substrate, via the point and/or points of attachment. Electrochemical reactions required to drive an electrochemical process occur at the surface of the secondary substrate.
Any suitable material may be used to construct the primary anode structure, referred to herein as the anode frame. Suitable materials must adequately provide a sturdy frame work and exhibit satisfactory electrical conductivity. Non-limiting examples of suitable materials for the anode frame include valve metals such as titanium, tantalum, niobium and zirconium. Further examples include copper conductors protected by titanium cladding. [0021]
The anode frame preferably provides a minimal amount or, more preferably, none of the anode's anodic surface area. Preferably, the anode frame provides less than about 1% of the anode's anodic surface area. Consequently, the anode frame is substantially free of any electrocatalytic surface coating. The anode frame is preferably not subjected to any coating or pre-treatment process utilized in applying an electrocatalytic coating to a substrate, which is further described herein. Preferably, less than about 5%, more preferably less than about 2%, and most preferably less than about 1% of the anode frame is coated with an electrocatalytic coating. [0022]
Since the anode frame does not contribute any substantial surface area to the anode's anodic surface, no minimum surface area is required for the anode frame. The minimum size and, consequently, the minimum surface area of the anode frame is the size and/or surface area required to adequately provide a sturdy, structural frame work, support a desired anodic surface area, conduct adequate electrical current, and provide a frame for matching the geometry of a corresponding cathode. No minimum size requirement for the anode frame allows for simplified geometries to be employed in constructing the anode frame. Simplified, and optionally smaller, designs require less labor to construct the anode frame (and consequently the anode) and the use of fewer and less expensive materials. [0023]
The present invention contemplates that the anode frame may exhibit any desired geometry and/or configuration. Anode frame configurations include simplified configurations such as, for example, the simple frame of [0024] primary anode 12 in FIG. 1. Additionally, it is contemplated that the anode frames may have complex, three-dimensional configurations. Anode frames exhibiting a three-dimensional configuration provide may provide, when a substrate is attached thereto, an anode structure, that allows for excellent current distribution to a corresponding cathode. Preferably, an anode frame according to the present invention I) exhibits a shape complimentary to a corresponding cathode, and/or ii) is shaped or formed such that upon attaching a substrate to the frame, an anode is formed exhibiting a shape complimentary to a corresponding cathode. Any design or configuration of the anode frame is contemplated, provided that the anode frame provides sufficient structural support to the anode.
Anodes according to the present invention also comprises a metal substrate. As previously described herein, a metal substrate is attached to the anode frame and provides the anode with the critical anodic surface areas utilized during an electrochemical process. In a preferred embodiment, a single metal substrate is employed to form the anodic surface are of the anode. However, the present invention contemplates the use of two or more metal substrates to form the anode's anodic surface area. Metal substrate, as used herein, refers to both a single metal substrate and a plurality of metal substrates that form the anodic surface area of an anode according to the present invention. [0025]
The metal substrate is constructed from any suitable substrate material. Preferably, the metal substrate is a valve metal including, but not limited to, titanium, tantalum, zirconium, niobium, and alloys thereof. A most preferred substrate material is titanium. The substrate material may be in the form of sheets, rods, tubing, and expanded metal mesh. Preferably the substrate material is in the form of expanded metal mesh, providing an open area in the substrate's surface that allows an electroplating solution to flow through the anode during an electrochemical process. The thickness of the metal substrate is preferably less than about 0.00165 m, and more preferably less than about 0.0010 m. Substrates having a thickness of less than about 0.00165 m are flexible and easily shaped, configured, and/or mated to exhibit a geometry that is complimentary to a corresponding cathode. Mating the anode geometry to the cathode geometry allows for excellent current distribution to all current density areas of a corresponding cathode. [0026]
Metal substrates employed in an anode according to the present invention include an electrocatalytic coating. The electrocatalytic coating allows electrochemical reactions to proceed at the anodic surface. Additionally, the electrocatalytic coating prevents metal substrates from corroding and/or dissolving, which may result in early failure of the anode. Non-limiting examples of suitable electrocatalytic coatings include platinum group metal oxide coatings. Exemplary platinum group metal oxide coatings include iridium oxide, palladium oxide, rhodium oxide, niobium oxide, tantalum oxide, ruthenium oxide, and platinum oxide. Other suitable electrocatalytic coatings include magnetite, ferrite, cobalt spinel, platinum metal, gold medal and mixed metal oxide coatings. [0027]
Electrocatalytic coatings can be formed on the metal substrate by thermal decomposition, plating, welding or some other method of attachment. [0028]
Anodes according to the present invention are constructed by attaching a metal substrate to an anode frame. Preferably, one metal substrate is attached to an anode frame. The present invention contemplates anodes comprising two or more metal substrates attached to an anode frame. Any number of metal substrates are attached to the anode frame, such that the substrate provide a desired anodic surface area. Preferably, the substrate is pre-coated before being attached to the anode frame. Preparation of the metal substrate is preferably performed prior to attaching the metal substrate to the anode frame. The substrate is attached to the anode frame by any suitable method, including but not limited to, welding, bonding, soldering, threading, crimping, and clamping. The point and/or points of attachment provide a point of electrical contact between the metal substrate and the anode frame. [0029]
Anodes according to the present invention are suitable as an electrode in any electrochemical process. The anodes are particularly suited as an anode in an aqueous electrochemical process such as, for example, an electroplating process for the electrodeposition of metals. [0030]
Method of Refurbishment [0031]
“Service life” as used herein refers to the time period in which an anode and/or substrate adequately provides an anodic surface (and thereby properly functions as an anode). Service life is expressed as either the number of times the anode is used, i.e., the number of individual uses or “rounds”, or any acceptable time unit, such as, for example, amp-hours (AH). [0032]
“Down time” as used herein refers to the time in which an anode is not in operation (in an electrochemical process). “Turn around time” as used herein refers to the period of time required to refurbish an anode and subsequently return it to operate in an electrochemical process. [0033]
“Pre-coated substrate” as used herein refers to a metal substrate, suitable for constructing an anode according to the present invention, having an electrocatalytic surface coating prior to attachment to an anode frame and/or prior to distribution to an end user. [0034]
Anodes according to the present invention are easily refurbished. Electrocatalytic coatings are depleted during an electrochemical process and thus exhibit a limited service life. Anodes and/or metal substrates having a depleted electrocatalytic coating are referred to herein as depleted anodes and/or depleted substrates. Refurbishing a depleted anode and/or substrate is accomplished by regenerating the anodic surface of the anode. Regenerating an anodic surface includes applying a fresh electrocatalytic coating to a surface. Refurbishing anodes according to the present invention includes removing a depleted substrate from the anode frame and attaching a separate metal substrate having a sufficient electrocatalytic coating to the anode frame. [0035]
In a preferred embodiment, the method for refurbishing an anode includes, in a first step, providing an anode comprising an anode frame and a metal substrate attached thereto, wherein the metal substrate includes an electrocatalytic coating. Secondly, the anode of the first step is employed in an electrochemical process. During the electrochemical process, the electrocatalytic coating is depleted or worn away from the metal substrate. A third step of the process includes removing the metal substrate from the anode frame. A fourth step includes applying an electrocatalytic coating, as previously described herein, to a second metal substrate. In a fifth step the coated metal substrate from the fourth step is attached to the anode frame from step three. The anode from the fifth step is subsequently employed in an electrochemical process. It is contemplated that the step of applying an electrocatalytic coating to a second metal substrate, i.e. step four, may be performed at any time prior to attaching the second metal substrate to the anode frame, i.e., step five. [0036]
The present method also contemplates i) disposing of, or ii) reusing a depleted substrate in a subsequent electrochemical process. A depleted metal substrate may be reused after it has been refurbished. Refurbishing a depleted metal substrate is accomplished, as previously described herein, by applying a fresh electrocatalytic coating to the depleted metal substrate. [0037]
If a depleted metal substrate is refurbished and subsequently reused to refurbish an anode according to the present invention, a separate metal substrate is not necessarily employed to refurbish the anode. Refurbishing an anode utilizing a single metal substrate requires i) removing the (depleted) substrate from the anode frame, ii) refurbishing the substrate by a applying a fresh electrocatalytic coating to the depleted substrate, and iii) attaching the refurbished metal substrate to the anode frame. The anode can not be used while the metal substrate is being refurbished, which may involve repeated coating applications that require a significant amount of time. [0038]
Most preferably, even if a depleted substrate is refurbished and reused for subsequent electrochemical processing, one or more additional separate anodic substrates are employed in the method of refurbishing an anode. Utilizing one or more additional separate anodic substrates to refurbish an anode allows for continued use of the anode for electrochemical processing. Specifically, down time is minimized and short turn around times are encountered. Utilizing a separate pre-coated substrate allows the anode to be quickly refurbished by replacing the depleted substrate with a fresh pre-coated substrate. Refurbishing an anode by utilizing separate pre-coated substrates is typically accomplished in about 5 minutes to about an hour. [0039]
A method for providing replacement anodes includes supplying anodes to a separate user. Preferably, an anode includes an anode frame and a metal substrate having an electrocatalytic coating attached to the anode frame. One or more additional pre-coated substrates coating are also supplied to the user. The user employs the anode in an electrochemical process. During the electrochemical process, the electrocatalytic coating is depleted from the substrate. The user then removes the substrate from the anode frame and subsequently refurbishes the anode by attaching one of the one or more additional pre-coated substrates to the anode frame. The above steps of removing the substrate having a depleted electrocatalytic coating and refurbishing the anode with the one or more additional pre-coated substrates is repeated by the user as is necessary. The user optionally returns depleted substrates to the supplier for refurbishment (of the substrate). Depleted substrates are refurbished, by the supplier or another suitable source, by applying a fresh electrocatalytic coating to the depleted substrate and/or substrates. Refurbished substrates are then returned to the user for further electrochemical processing. It is also contemplated that the user may dispose of substrates after substantial depletion of the electrocatalytic coating, i.e., after the substrate's service life has expired. Additional coated substrates may have to be supplied to the user if the user disposes of the depleted substrate(s). [0040]
Without intending to limit the scope of the invention, the following examples illustrate the advantages of the present invention anode. [0041]

EXAMPLE I

An anode according to the present invention was constructed for an electroplating process. The anode comprised an anode frame and a disposable metal substrate attached to the anode frame. The anode frame was constructed of fabricated titanium metal. The removable substrate was expanded titanium mesh and was coated with an iridium oxide coating (electrocatalytic coating) before the substrate was attached to the frame. The metal substrate had an effective anodic surface area of 0.042 m[0042] ². The total surface of the anode was 0.084 m². The anode according to the present invention weighed about 0.41 kg. Refurbishing the anode was accomplished by removing the metal substrate and attaching a separate pre-coated substrate to the frame. Refurbishing the anode was accomplished in about an hour. The depleted substrate was discarded.

COMPARATIVE EXAMPLE I

A conventional-type anode for the same plating process was constructed of a series of separate plates. A unitary anode structure was formed by welding the plates together with connecting members. The conventional anode had an anodic surface area of 0.048 m[0043] ². Only the anodic surface, i.e., the plates, were coated with an electrocatalytic coating. However, treating and recoating the anodic surface of the anode required handling the entire anode including areas not coated. The process of coating and/or refurbishing the anode required 14 days. The conventional anode weighed about 0.95 kg.

EXAMPLE II

An anode (A) exhibiting a pronounced three-dimensional shape had a surface area of about 0.11 m[0044] ². The surface was provided by an expanded titanium mesh substrate with an open area of about 74%. The anode required 10.4 g/m²of catalyst coating. Total processing time of anode (A), i.e., coating, treatment, refurbishing, etc., was ten days. The anode (A) had a service life of 350 uses. 120 anodes were processed per production lot.
Anode (A) was converted into a two-part anode according to the present invention, anode (B), by cutting away the titanium mesh substrate of anode (A), and replacing it with a separate pre-coated substrate. The substrate utilized in anode (B) was an expanded titanium mesh substrate having a surface area of about 0.11 m[0045] ²and an open area of about 49%. Consequently, anode (B) exhibited an anodic surface area approximately twice the anodic surface area of anode (A). The substrate of anode (B) required 20.4 g/m²of catalyst coating. Anode (B) had a service life of 700 uses, or twice that of anode (A). 192 substrates for anode (B) were processed per production cycle. Processing time for the substrates of anode (B) was three days. Substrates of anode (B) were disposed of after their service life expired and replaced with a pre-coated substrate.
The foregoing description is, at present, considered to be the preferred embodiments of the present invention. However, it is contemplated that various changes and modifications apparent to those skilled in the art may be made without departing from the present invention. Therefore, the foregoing description is intended to cover all such changes and modifications encompassed within the spirit and scope of the present invention, including all equivalent aspects. [0046]

Claims

What is claimed:

1. An anode for an aqueous electrochemical process, the anode comprising:

an anode frame; and

a titanium mesh or sheet substrate including an electrocatalytic coating, said titanium mesh substrate attached to the anode frame, wherein the anode frame provides electrical conductivity and the titanium mesh substrate provides an anodic surface.

2. The anode according to claim 1, wherein the anode frame is substantially free of an electrocatalytic coating.

3. The anode according to claim 1, wherein the electrocatalytic coating is a metal oxide selected from the group consisting of iridium oxide, tantalum oxide, ruthenium oxide, platinum oxide, and combinations thereof.

4. The anode according to claim 1, wherein the anode frame exhibits a geometry complimentary to a corresponding cathode.

5. The anode according to claim 1, wherein the titanium substrate is a flexible mesh sheet.

6. The anode of claim 5, wherein the titanium mesh sheet exhibits a geometry complimentary to a corresponding anode.

7. The anode according to claim 1, wherein the titanium mesh substrate is removable from the anode frame.

8. The anode according to claim 1, wherein the thickness of the titanium mesh substrate is less than about 0.00165 meters.

9. The anode according to claim 1, wherein said anode frame comprises titanium.

10. A method for refurbishing an anode comprising the steps of:

1) providing a anode comprising an anode frame and a removable metal substrate attached thereto, the metal substrate comprising an electrocatalytic coating;

2) employing the anode of step (1) in an electrochemical process and depleting the electrocatalytic coating from the metal substrate;

3) removing the metal substrate from the anode frame;

4) applying an electrocatalytic coating to a second metal substrate;

5) attaching the metal substrate of step (4) to the anode frame of step (3);

6) employing the anode of step (5) in an electrochemical process.

11. The method according to claim 10, wherein step (4) may be performed at any time prior to step (5).

12. The method according to claim 10, further comprising the step of disposing of the first metal substrate after removing the first metal substrate from the anode frame.

13. The method according to claim 10, further comprising the steps of:

providing a refurbished first metal substrate by applying a fresh electrocatalytic coating to the first metal substrate;

depleting the electrocatalytic coating from the second metal substrate by an electrochemical process;

removing the second metal substrate from the anode frame; and

attaching the refurbished first metal substrate to the anode frame thereby providing a refurbished anode.

14. A method for providing replacement anodes for electrochemical processing, the method comprising;

supplying an anode to a user, the anode comprising an anode frame and a metal substrate having an electrocatalytic coating attached thereto; and

supplying one or more additional pre-coated metal substrates to the user, wherein the user a) depletes the electrocatalytic coating from the metal substrate during an electrochemical process, b) removes the metal substrate from the anode frame after the electrochemical process, c) refurbishes the anode by attaching one of the one or more additional metal substrates to the anode frame, and d) repeats a-c as desired.

15. The method according to claim 14, wherein the user returns the metal substrate and the one or more additional metal substrates having a depleted electrocatalytic coating.

16. The method according to claim 15, further comprising applying a fresh electrocatalytic coating to the metal substrate and the one or more additional metal substrates returned by the user.

17. The method according to claim 14, wherein the one or more additional metal substrates supplied to the user are replacement disposable anodes.