KR101950169B1 - Electrolytic generation of manganese (ⅲ) ions in strong sulfuric acid - Google Patents

Abstract

An electrolytic bath, and a method for electrochemical oxidation of manganese (II) ion to manganese (III) ion in the electrolytic bath are described. (1) an electrolyte solution of manganese (II) ion in a solution of 9 to 15 moles sulfuric acid; (2) a cathode immersed in the electrolyte solution; And (3) an anode immersed in the electrolyte solution and spaced apart from the cathode. Various anode materials are disclosed, including vitreous carbon, reticulated vitreous carbon and woven carbon fibers.

Description

ELECTROLYTIC GENERATION OF MANGANESE (III) IONS IN STRONG SULFURIC ACID FOR MANGANESE (III)

Cross-reference to related application

This application is a continuation-in-part of the presently pending patent application No. 13 / 356,004 filed on January 23, 2012, the subject matter of which is incorporated herein by reference in its entirety.

Technical field

The present invention generally relates to a process for electrolytically producing manganese (III) ions in strong sulfuric acid using an improved anode.

It is well known in the art to metallize non-conductive substrates (i.e., plastics) for metal for various purposes. Plastic moldings are relatively inexpensive to manufacture, and metal plated plastics are used in many applications. For example, metal-plated plastics are used for decorative purposes and are used in the manufacture of electronic devices. One example of a decorative application includes automotive parts such as trim. An example of an electronic application includes a printed circuit where the metal plated in a selective pattern constitutes the conductor of the printed circuit board and the metal plated plastic is used for EMI shielding. While ABS resins are the most common plated plastic for decorative purposes, phenolic and epoxy resins are the most common plated plastics for the production of printed circuit boards.

Plating on plastic surfaces is used in the manufacture of various consumer goods items. Plastic moldings are relatively inexpensive to manufacture and plated plastics are used in many applications including automotive trim. Plating of plastics involves several stages. The first stage is to provide a suitable surface for the adsorption of a palladium catalyst which is typically applied to catalyze the deposition of the initial metal layer from an autocatalytic nickel or copper plating process And etching the plastic to provide it. Thereafter, deposits of copper, nickel and / or chromium can be applied.

Initial etching of plastic components is an integral part of the overall process. However, only certain types of plastic components are suitable for plating. The most common types of plastics for electroplating are acrylonitrile / butadiene / styrene (ABS) or a blend of ABS and polycarbonate (ABS / PC). The ABS consists of two phases. The first phase is a relatively hard phase consisting of an acrylonitrile / styrene copolymer and the second phase is a softer polybutadiene phase.

Recently, these materials are almost entirely etched using a mixture of chromic acid and sulfuric acid, and the mixture is very effective as an etchant for ABS and ABS / PC. The polybutadiene phase of the plastic contains a double bond in the polymer backbone which is oxidized by chromic acid to effect complete decomposition and dissolution of the exposed polybutadiene on the surface of the plastic to provide an effective etch on the surface of the plastic.

One problem with conventional chromic acid etching steps is that chromic acid is a known carcinogen, which is becoming increasingly regulated, and wherever possible it is urged to replace the use of chromic acid with a safer alternative. In addition, the use of a chromic acid etchant can also be used to reduce the toxicity of the chromium compound (which makes it difficult to discard), the chromic acid residue remaining on the polymer surface (which inhibits electroless deposition) Including the difficulty of rinsing the residue. In addition, hot hexavalent chromium sulphate solutions are undesirable for operators. Burns and bleeding are common in workers routinely associated with such chromium etching solutions. It is therefore highly desirable to develop a safer alternative to the acidic chromium etching solution.

Early attempts at replacing the use of chromic acid to etch plastics have typically focused on the use of permanganate ions as a replacement for chromic acid. The use of permanganates in combination with acids is described in U.S. Patent No. 4,610,895 to Tubergen et al., The entire contents of which are incorporated herein by reference. Thereafter, the use of permanganates in combination with ionic palladium activation stages has been proposed in US Patent Publication No. 2005/019958 to Bengston, the entire contents of which are incorporated herein by reference. The use of acid permanganate solutions in conjunction with perhalo ions (e. G., Perchlorate or periodate) is described in U.S. Patent Application Publication No. 2009/0092757 to Satou, the entire content of which is incorporated herein by reference. Lt; / RTI > Finally, the use of permanganate ions in the absence of alkali or alkaline earth metal cations is described in Enthone International Publication No. WO 2009/023628, the entire contents of which are incorporated herein by reference.

The permanganate solution is also described in U.S. Patent No. 3,625,758 to Stahl et al., The entire contents of which are incorporated herein by reference. Stahl suggests the suitability of chromium and sulfuric acid baths or permanganate solutions for surface preparation. U.S. Patent No. 4,948,630 to Courduvelis et al., Which is incorporated herein by reference in its entirety, has an oxidation potential higher than the oxidation potential of a permanganate solution and oxidizes manganate ions to permanganate ions Lt; RTI ID = 0.0 > permanganate < / RTI > solution, which also contains a material such as sodium hypochlorite. U.S. Patent No. 5,648,125 to Cane, the entire contents of which is incorporated herein by reference, describes the use of an alkaline permanganate solution comprising potassium permanganate and sodium hydroxide, wherein the permanganate solution is heated at elevated temperatures, That is, about 165 [deg.] F to about 200 [deg.] F. US Pat. No. 4,042,729, issued to Polichette et al., The entire contents of which is incorporated herein by reference, describes an etching solution comprising water, permanganate ions and manganate ions, wherein the permanganate ion The molar ratio of manganate ion to pH is controlled and the pH of the solution is maintained at 11-13.

As can be readily seen, a number of etching solutions have been proposed as alternatives to chromic acid in processes for making nonconductive substrates for metallization. None of these processes have, however, been proved satisfactory for various economic, performance and / or environmental reasons, and thus none of these processes have achieved commercial success or have been successfully used as industrial alternatives for chromate etching Was not accepted. In addition, the stability of the etching solution is also poor, which may lead to the formation of manganese dioxide sludge.

The present inventors have noted in this invention the tendency of permanganate solutions to form sludge and undergo self-degradation. Under strongly acidic conditions, permanganate ions can react with hydrogen ions to produce manganese (II) ions and water according to the following reaction:

_{^{4MnO 4 - + 12-H +}} → 4Mn 2 + + 6H 2 O + 5O 2 (1)

The manganese (II) ions formed by this reaction can then react further with permanganate ions according to the following reaction to form sludge of manganese dioxide:

^{_{2MnO 4 - + 2H 2 O +}} 3Mn 2 + → 5MnO 2 + 4H + (2)

Thus, formulations based on strong acid permanganate solutions are inherently unstable regardless of whether permanganate ions are added by alkali metal salts of permanganate salts or electrochemically generated in situ. The poor chemical stability of acidic permanganates compared to the chromic acid etchings used in recent years makes this virtually useless for large commercial applications. The alkaline permanganate etchant is more stable and widely used in the printed circuit board industry for etching epoxy printed circuit boards, but alkaline permanganate is not an effective etchant for plastics such as ABS or ABS / PC. Thus, it appears that manganese (VII) has not obtained broad commercial recognition as an etchant for such materials.

Attempts to etch ABS without chromic acid involve the use of electrochemically generated silver (II) or cobalt (III). Certain metals can be anode oxidized to a highly oxidizing oxidation state. For example, manganese (II) can be oxidized to a permanganate (manganese VI), cobalt can be oxidized from cobalt (II) to cobalt (III) .

Currently, there is no commercially available suitable etchant for plastics based on permanganate (in acidic or alkaline form), based on manganese in another oxidation state, or by using other acids or oxidants.

Thus, there remains a need in the art for improved etchants for the production of plastic substrates for subsequent electroplating that are chromium-free and commercially acceptable.

An object of the present invention is to provide an etching solution for a plastic substrate which does not contain chromic acid.

It is another object of the present invention to provide a commercially acceptable etchant for plastic substrates.

It is still another object of the present invention to provide an etching solution for a plastic substrate based on manganese ions.

It is yet another object of the present invention to provide an electrode which is suitable for use in a strong acid oxidizing electrolyte but which is not decomposed by the electrolyte.

It is a further object of the present invention to provide an electrode suitable for the production of manganese (III) ions in commercially acceptable strong sulfuric acid.

To this end, the present invention relates generally to electrodes suitable for electrochemical oxidation of manganese (II) ions to manganese (III) ions in a strong sulfuric acid solution.

In addition,

An electrolyte solution containing manganese (III) ions in a solution of an acid, preferably 9 to 15 moles of sulfuric acid;

A cathode in contact with the electrolyte solution; And

An anode in contact with the electrolyte solution wherein the anode comprises a material selected from the group consisting of vitreous carbon, reticulated vitreous carbon, woven carbon fibers, and combinations of one or more of the foregoing. )

And an electrolytic cell including the electrolytic cell.

In yet another aspect,

Providing an electrolyte comprising a solution of manganese (II) ions in a solution of an acid, preferably 9 to 15 moles sulfuric acid, in an electrolytic bath comprising an anode and a cathode;

Applying a current to the anode and the cathode of the electrolytic cell; And

Oxidizing the electrolyte to form manganese (III) ions, wherein the manganese (III) ions form a metastable complex;

To a manganese (II) ion to a manganese (III) ion.

The inventors of the present invention have found that trivalent manganese can be easily produced by electrolysis at a low current density of divalent manganese ions in strong sulfuric acid. More particularly, the inventors of the present invention have found that a solution of trivalent manganese ions in a strongly acidic solution can etch ABS.

Trivalent manganese is unstable and highly oxidative (a standard oxidation-reduction potential of 1.51 as compared to a conventional hydrogen electrode). In solution, trivalent manganese is very rapidly disproportionated to manganese dioxide and divalent manganese through the following reaction:

_{^{2Mn 3 + + 2H 2 O →}} MnO 2 + Mn 2 + + 4H + (3)

However, in strong sulfuric acid solutions, trivalent manganese ions are metastable and form a sulfate complex of cherry purple / red. The present inventors have found that this sulfate complex is a suitable medium for etching the ABS and has a number of advantages over the chromium-free etchant described above.

In one aspect,

Providing an electrolyte comprising a solution of manganese (II) ions in an acid solution in an electrolytic bath comprising an anode and a cathode;

Applying a current to the anode and the cathode of the electrolytic cell; And

Oxidizing the electrolyte to form manganese (III) ions, wherein the manganese (III) ions form a metastable complex;

To a process for producing a solution capable of etching a plastic substrate.

In a preferred embodiment, the plastic substrate comprises ABS or ABS / PC.

Although both phosphoric acid and sulfuric acid are considered suitable for the composition of the present invention, in a preferred embodiment, the acid is sulfuric acid. At ambient temperature, the half life of manganese (III) in 7M sulfuric acid is approximately 2 years. In comparison, the half life of manganese (III) ion at similar concentration in 7M phosphoric acid was approximately 12 days. Much higher stability of manganese (III) ions in sulfuric acid has been suggested due to the formation of manganose-sulfate complexes and higher concentrations of available hydrogen ions in the sulfuric acid solution. A further problem associated with the use of phosphoric acid is the limited solubility of manganese phosphate (III). Thus, although additional inorganic acids such as phosphoric acid may be useful in the compositions of the present invention, it is generally preferred to use sulfuric acid.

The remarkable stability of the manganese (III) ion in strong sulfuric acid provides the following advantages in use:

1) Since Mn (III) ions are formed at low current densities, the power required for the process is typically very low.

2) Since the anode operates at a very low current density, cathode reduction of Mn (III) ions can be prevented using a cathode that is smaller than the anode area. This eliminates the need for a divided cell and simplifies the operation of the etchant regeneration electrolytic cell.

3) Since no permanganate ion is produced in the process, there is no possibility of producing manganese oxide in the solution (which is a significant risk for safety because of its violent explosiveness).

4) Because of the high stability of Mn (III) ions in strong sulfuric acid, the etchant can be sold in ready-to-use conditions. In manufacturing, the etchant requires only a small regenerative electrolytic bath on the tank side to maintain the Mn (III) content of the etchant and prevent the build-up of Mn (II) ions.

5) Since other etching processes are based on permanganate salts, the reaction of permanganate and Mn (II) ions results in a rapid "sludging" with manganese dioxide and a very short lifetime of the etching. This should not be an issue for the Mn (III) etchant (although there may be some disproportionation over time).

6) The electrolytic preparation of Mn (III) according to the invention does not produce any toxic gases. Although some hydrogen may be produced at the cathode, due to the low power requirement, this will be less than that produced by multiple plating processes.

As described herein, in a preferred embodiment, the acid is sulfuric acid. The concentration of sulfuric acid is preferably about 9 moles to about 15 moles. The concentration of sulfuric acid is important in this process. At a concentration of less than about 9 moles, the etch rate slows, and when more than about 14 moles, the solubility of manganese ions in the solution is low. In addition, very high concentrations of sulfuric acid tend to absorb moisture from the air and are dangerous to handle. Thus, in a most preferred embodiment, the concentration of sulfuric acid is from about 12 to 13 moles, a concentration that is sufficiently dilute to be able to safely add water to the etchant and strong enough to optimize the etch rate of the plastic. At this sulfuric acid concentration, manganese sulfate of about 0.08 M or less can be dissolved at the desired operating temperature of the etch. For optimal etching, the concentration of manganese ions in the solution should be high enough to be attainable.

The manganese (II) ion is preferably selected from the group consisting of manganese sulfate, manganese carbonate and manganese hydroxide, but other similar sources of manganese (II) ions known in the art may also be useful in the practice of the present invention. The concentration of the manganese (II) ion may range from about 0.005 mole to the saturation concentration. In one embodiment, the electrolyte also comprises colloidal manganese dioxide. This can be formed to some extent as a natural result of the disproportionation of manganese (III) in solution, or it can be intentionally added.

Manganese (III) ions can be conveniently generated by oxidation of manganese (II) ions by electrochemical means. It may also be generally desirable that the electrolyte not contain any permanganate ions.

In another aspect, the present invention comprises dipping a platable plastic into a metastable sulphate complex for a period of time to etch the surface of the platable plastic. In one embodiment, the platable plastic is immersed in the solution at a temperature of 30 to 80 占 폚. The etch rate increases with temperature and slows below 50 ° C. The upper limit of the temperature is determined by the nature of the plastic being etched. In the preferred embodiment, especially when ABS material is etched, since ABS begins to distort above 70 ° C. The temperature of the electrolyte is maintained at about 50 to about 70 < 0 > C. The immersion time of the plastic in the electrolyte is preferably about 20 minutes to about 30 minutes.

In this way, the etched articles are subsequently electrodeposited using conventional pretreatment for plated plastic, or the etched surface of the plastic is used to enhance the adhesion of paint, lockers or other surface coatings .

As described in the following embodiments, the inventors of the present invention have found that oxidation can be diffusion-controlled by the cyclic voltammetry at the concentration of manganese (II) ions used in the etching solution of the present invention, It has been found that efficient agitation of the etching solution during the process is required.

In another preferred embodiment, the present invention generally relates to an electrolyte capable of etching a platable plastic, wherein said electrolyte comprises a solution of manganese (III) in an acid solution. The acid solution is preferably sulfuric acid.

The anodes and cathodes useful in the electrolytic cell described herein may include various materials. The cathode may comprise a material selected from the group consisting of platinum, platinized titanium, niobium, iridium-coated titanium, and lead. In one preferred embodiment, the cathode comprises platinum or titanium platinum. In another preferred embodiment, the cathode comprises lead. The anode may also include titanium platinum, platinum, iridium / tantalum oxide, niobium or other suitable material, preferably platinum or titanium platinum.

In another preferred embodiment, the inventors of the present invention have found that the anode may comprise a glassy carbon and that the use of a glassy carbon anode provides a commercially suitable electrode. The present inventors have found that although a combination of manganese (III) ions and strong sulfuric acid (i.e., 9-15 moles) can etch ABS plastic, the etchant is also very aggressive to the electrodes required to produce manganese (III) ions Respectively. In particular, an anode having a titanium substrate can be rapidly degraded by an etching solution.

Thus, in an attempt to find a more suitable electrode material, various other electrode materials, including lead and graphite, have been tested. It has been found that lead is rapidly attacked by the etchant when used as an anode (although found to be suitable for use as a cathode), and the graphite anode is quickly broken down. However, it has been found that the vitreous carbon and the network vitreous carbon are more robust, and when manganese (III) ions are applied when a current of 0.1 to 0.4 A / dm 2 (based on the nominal surface area) is applied, Can be generated. Thus, as described herein, an anode made of glassy carbon can be used as an electrode. It has further been found that the anode can be made from woven carbon fibers, since the vitreous carbon and the reticulated vitreous carbon are not cost effective to use as electrodes in commercial applications.

Carbon fibers are made from fibers of polyacrylonitrile (PAN). These fibers undergo oxidation at elevated temperatures and then undergo carbonization at very high temperatures in an inert atmosphere. The carbon fibers are then woven into a sheet, which is typically used in combination with various resin systems to produce high strength members. In addition, the carbon fiber sheet has excellent electrical conductivity, and the fiber typically has a turbostratic (i.e., irregular layer) structure. Although not intending to be bound by theory, the present inventors believe that this is a structure that makes carbon fibers highly effective as electrodes. The SP ² hybridized carbon atoms in the lattice provide good electrical conductivity while the SP ³ hybridized carbon atoms bond the graphite layers together and lock them in place, thus providing excellent chemical resistance.

Preferred materials for use in the electrodes of the present invention include woven carbon fibers that contain at least 95% carbon and are not impregnated with a resin. To facilitate handling and weaving processes, carbon fibers are typically sized with epoxy resin, which can account for less than 2% of the fiber weight. At these low percentages, when used as electrodes, the epoxy sizing is quickly removed by the high sulfuric acid content of the etch. This may result in some initial discoloration of the etchant, but does not affect performance. After this initial "running in" stage, the anode appears to be resistant to electrolytes and is effective in oxidizing manganese (II) ions to manganese (III).

The anode can be fabricated by mounting a woven carbon fiber material within a suitable frame using equipment made for electrical contact. It is also possible to use carbon fibers as cathodes in the production of manganese (III) ions, but it is more convenient to use lead, especially since the cathodes are much smaller than the anode when an unseparated electrolyzer is used.

In addition, for efficient production of manganese (III) ions, it is generally necessary to use a larger anode area than the cathode area. Preferably, the area ratio of anode to cathode is at least about 10: 1. By this means, the cathode can be immersed directly in the electrolyte and it is not necessary to have a partitioned electrolyzer (the process operates with a partitioned cell array, but this will result in unnecessary complexity and cost).

In yet another preferred embodiment,

An electrolyte solution containing manganese (III) ions in an acid solution;

A cathode in contact with the electrolyte solution; And

An anode in contact with the electrolyte solution, wherein the anode comprises a material selected from the group consisting of vitreous carbon, reticulated vitreous carbon, woven carbon fibers, and combinations of one or more of the foregoing.

To the electrolytic bath.

The invention will now be illustrated by reference to the following non-limiting examples:

compare Example  One:

A solution of 0.08 mole manganese (II) sulfate in 12.5 moles sulfuric acid (500 ml) was heated to 70 占 폚 and a platable grade ABS piece was immersed in the solution. Even after 1 hour of immersion in the solution, the test panel was not discernibly etched and the surface was not "wet" during rinsing and failed to support the undamaged water film.

Example  One:

The solution of Comparative Example 1 was electrolyzed by immersing a titanium anode platinum of 1 dm 2 in area and a platinum titanium cathode having a surface area of 0.01 dm 2 in the solution and applying an electric current of 200 mA for 5 hours.

During this electrolysis period, the solution was observed to be discolored from almost colorless to very dark purple / red. It was confirmed that no permanganate ions were present.

The solution was then heated to 70 DEG C and a plated grade ABS piece was immersed in the solution. After 10 minutes of immersion, the test piece supported a water film that was completely wet and not destroyed after rinsing. After immersion for 20 minutes, the sample was washed with water, dried and examined using a scanning electron microscope (SEM). These tests revealed that the test piece was significantly etched and a number of etch pits were visible.

Example  2:

A solution containing 12.5 M sulfuric acid and 0.08 M manganese sulfate (II) was electrolyzed at a current density of 0.2 A / dm 2 using a titanium-platinum anode. A titanium platinum cathode having an area of less than 1% of the anode area was used to prevent cathode reduction of Mn (III) ions generated in the anode. The electrolysis was performed long enough to allow sufficient coulombs to pass through to oxidize all manganese (II) ions to manganese (III). The resulting solution was dark cherry purple / red. No permanganate ion was generated during this step. This was also confirmed by visible spectroscopy, and Mn (III) ion produced a completely different absorption spectrum from the solution of permanganate salt.

Example  3:

The etching solution prepared as described above in Example 3 was heated to 65-70 占 폚 on a magnetic stirrer / hot plate and the test piece of ABS was immersed in the solution for 20 minutes to 30 minutes. Some of these test materials were tested with SEM and some were processed in plastic pretreatment sequence (M-neutralization reduction, pre-dipping, activation, accelerated, electroless nickel, 25-30 micron copper plating) . These test materials were then annealed and tested for peel strength using an Instron instrument.

The peel strength test conducted on the test materials plated for 30 minutes proved that the peel strength was variable from about 1.5 to 4 N / cm.

A cyclic voltammogram was obtained from a solution containing 12.5 M sulfuric acid and 0.08 M manganese sulfate using a rotating disk electrode (RDE) having a surface area of 0.196 cm 2 at various rotational speeds. A Model 263A constant-voltage potentiostat and a silver / silver chloride reference electrode were used with the RDE.

In all cases, the forward scan is approximately 1.6V vs.. Ag / AgCl peaked and then maintained a plateau of approximately 1.75 V until the current increased. The reverse scan caused a similar flattening (with slightly lower current and a peak of about 1.52V). The correlation of these results to the electrode rotation rate indicates that mass transport control is a key factor in the mechanism. The flattened region represents the potential range in which Mn (III) ions are formed by electrochemical oxidation.

The constant-voltage constant-current scan (potentiostatic scan) was performed at 1.7V. It was observed that the current increased with the passage of time after the initial fall. The current density at this potential varied from 0.15 to 0.4 A / dm 2.

After the experiment, a galvanostatic measurement was carried out at a constant current density of 0.3 A / dm 2. Initially, the applied current density was achieved up to a potential of about 1.5 V, but as the experiment progressed, a potential increase to about 1.75 V was observed after about 2400 seconds.

After etching for more than 10 minutes, the surface of the ABS test material was observed to support the water film completely wetted and not destroyed after rinsing. After a period of 20 minutes or 30 minutes, the panel was noticeably etched.

compare Example  2:

An electrode containing graphite and having a nominal measured surface area of 1 dm 2 was immersed in 500 ml of a solution containing 0.08 M manganese sulfate in 12.5 M sulfuric acid at a temperature of 65 ° C. In this electrolytic cell, the cathode was a piece of lead with a nominal measurement surface area of 0.1 dm 2. A current of 0.25 amps was applied to the electrolyzer to provide a nominal anode current density of 0.25 A / dm 2 and a nominal cathode current density of 2.5 A / dm 2.

The graphite anode was observed to break down quickly and degrade in less than one hour of electrolysis. In addition, manganese (II) No oxidation from ion to manganese (III) was observed.

compare Example  3:

Electrodes containing a titanium substrate coated with a mixed tantalum / iridium oxide coating (50% tantalum oxide, 50% iridium oxide) and having a nominal measurement surface area of 1 dm 2 were coated with 0.08 M manganese sulfate ≪ / RTI > In this electrolytic cell, the cathode was a piece of lead with a nominal measurement surface area of 0.1 dm 2. A current of 0.25 amps was applied to the electrolyzer to provide a nominal anode current density of 0.25 A / dm 2 and a nominal cathode current density of 2.5 A / dm 2.

It has been observed that manganese (III) is formed rapidly in the solution and that the resulting solution can etch ABS plastic and produce good adhesion upon subsequent electroplating of the treated plastic. However, after a period of 2 weeks of operation (electrolysis of the solution for 8 hours / day), the coating peels off the titanium substrate and the titanium substrate itself is observed to dissolve in the solution.

compare Example  4:

An electrode containing a titanium substrate coated with platinum and having a nominal measured surface area of 1 dm 2 was immersed in 500 ml of a solution containing 0.08 M manganese sulfate in 12.5 M sulfuric acid at a temperature of 65 ° C. In this electrolytic cell, the cathode was a piece of lead with a nominal measurement surface area of 0.1 dm 2. A current of 0.25 amps was applied to the electrolyzer to provide a nominal anode current density of 0.25 A / dm 2 and a nominal cathode current density of 2.5 A / dm 2.

It has been observed that manganese (III) is formed rapidly in the solution and that the resulting solution can etch ABS plastic and produce good adhesion upon subsequent electroplating of the treated plastic. However, after a period of 2 weeks of operation (electrolysis of the solution for 8 hours / day), the coating peels off the titanium substrate and the titanium substrate itself is observed to dissolve in the solution.

Example  4:

An electrode containing glassy carbon and having a nominal measured surface area of 0.125 dm 2 was immersed in 100 ml of a solution containing 0.08 M manganese sulfate in 12.5 M sulfuric acid at a temperature of 65 캜. In this electrolytic cell, the cathode was a piece of platinum wire with a nominal measured surface area of 0.0125 dm 2. A current of 0.031 amps was applied to the cell to provide a nominal anode current density of 0.25 A / dm 2 and a nominal cathode current density of 2.5 A / dm 2.

It has been observed that manganese (III) is formed rapidly in the solution and that the resulting solution can etch ABS plastic and produce good adhesion upon subsequent electroplating of the treated plastic. The electrode did not appear to be affected until the extended electrolysis period.

Example  5:

An electrode comprising a piece of woven carbon fiber (Panex 35 50K Tow with 1.5% epoxy sizing, the Zoltek Corporation) was mounted on a plastic frame made of polyvinylidene fluoride (PVDF) . The electrode with a nominal measuring area of 1 dm 2 was immersed in 500 ml of a solution containing 0.08 M manganese sulfate in 12.5 M sulfuric acid at a temperature of 65 ° C. In this electrolytic cell, the cathode was a piece of lead with a nominal measurement surface area of 0.1 dm 2. A current of 0.25 amps was applied to the electrolyzer to provide a nominal anode current density of 0.25 A / dm 2 and a nominal cathode current density of 2.5 A / dm 2.

It has been observed that manganese (III) is formed rapidly in the solution and that the resulting solution can etch ABS plastic and produce good adhesion upon subsequent electroplating of the treated plastic. The electrode did not appear to be affected until the extended electrolysis period. Electrolysis was carried out using these electrodes for 2 weeks and no observable deterioration was detected. Due to the low cost of these materials and their availability, they are suitable for a number of commercial applications.

These experimental results show that manganese (III) ions are produced by electrosynthesis using manganese (II) ions in relatively high concentrations of sulfuric acid and by working at low current densities using platinum or titanium platinum anodes And further improvement of the process by using a glassy carbon or carbon fiber anode can be realized.

Claims (36)

An electrolyte solution containing manganese (III) ions in a solution of an acid;
A cathode in contact with the electrolyte solution; And
An anode contacting the electrolyte solution,
Lt; / RTI >
Wherein the anode comprises a material selected from the group consisting of vitreous carbon, reticulated vitreous carbon, woven carbon fiber, and combinations of one or more of the foregoing,
Wherein the anode has a current density of 0.1 to 0.4 A / dm 2. The electrolytic cell of claim 1, wherein the anode comprises glassy carbon. The electrolytic cell of claim 1, wherein the anode comprises woven carbon fibers. 4. An electrolyzer according to claim 3, wherein the woven carbon fibers have a turbostratic structure. The electrolytic cell of claim 1, wherein the solution of acid comprises a solution of sulfuric acid. 4. An electrolytic cell according to claim 3, wherein said woven carbon fibers comprise at least 95% carbon, based on the weight of said woven carbon fibers. The electrolytic cell of claim 1, wherein the cathode comprises a material selected from the group consisting of platinum, platinized titanium, iridium / tantalum oxide, niobium, and lead. 8. The electrolytic cell of claim 7, wherein the cathode comprises lead. 6. An electrolytic cell according to claim 5, wherein the solution of acid comprises from 9 to 15 moles of sulfuric acid. Providing an electrolyte in the electrolytic bath comprising a solution of manganese (II) ions in an acid solution, said electrolytic bath comprising an anode and a cathode, wherein the anode is selected from the group consisting of vitreous carbon, reticulated vitreous carbon and woven carbon fiber Comprising the steps of:
Applying an electric current between the anode and the cathode, wherein the current density of the anode is 0.1 to 0.4 A / dm 2; And
(III) ion by oxidizing the electrolyte, wherein the manganese (III) ion forms a metastable complex
(II) ion to manganese (III) ion. The method of electrochemical oxidation of manganese (II) ion to manganese (III) ion according to claim 10, wherein the acid solution contains sulfuric acid. 11. The method of claim 10, wherein the acid solution comprises a 9 to 15 moles sulfuric acid solution, from a manganese (II) ion to a manganese (III) ion. 11. The method of claim 10, further comprising the step of contacting the platable plastic with the metastable composite for a period of time to etch the platable plastic. Oxidation method. The method of electrochemical oxidation according to claim 12, wherein the sulfuric acid has a concentration of 12 to 13 moles from manganese (II) ion to manganese (III) ion. The method of electrochemical oxidation according to claim 10, wherein the manganese (II) ion is derived from a compound selected from the group consisting of manganese sulfate, manganese carbonate and manganese hydroxide, from manganese (II) ion to manganese (III) ion. 11. The method of claim 10, wherein the solution further comprises a colloidal manganese manganese. 11. The method of claim 10, wherein the solution further comprises colloidal manganese dioxide. The method for electrochemical oxidation of manganese (II) ion to manganese (III) ion according to claim 10, wherein the concentration of manganese (II) ion in the electrolyte is 0.005 mol to a saturation concentration. 11. The method of claim 10, wherein the cathode comprises a material selected from the group consisting of platinum, titanium platinum, iridium / tantalum oxide, niobium and lead, an electrochemical oxidation method from manganese (II) . 19. The method of electrochemical oxidation of manganese (II) ions to manganese (III) ions according to claim 18, wherein the cathode comprises lead. 19. The method of electrochemical oxidation of manganese (II) ion to manganese (III) ion according to claim 18, wherein the cathode contains titanium platinum or platinum. The method of electrochemical oxidation of manganese (II) ion to manganese (III) ion according to claim 10, wherein the anode comprises glassy carbon. 11. The method of claim 10, wherein the anode comprises a woven carbon fiber, from a manganese (II) ion to a manganese (III) ion. 23. The method of claim 22, wherein the woven carbon fibers have a turbo-static structure, from electrochemical oxidation of manganese (II) ions to manganese (III) ions. 23. The method of claim 22, wherein the woven carbon fibers are made from fibers of polyacrylonitrile, from electrochemical oxidation of manganese (II) ions to manganese (III) ions. 23. The method of claim 22, wherein the woven carbon fiber comprises manganese (II) ions and manganese (III) ions, wherein the woven carbon fibers comprise 95% or more carbon and are impregnated with less than 2% / RTI > The method of electrochemical oxidation according to claim 10, wherein the area of the anode is larger than the area of the cathode, from manganese (II) ion to manganese (III) ion. 11. The method of claim 10, wherein the temperature of the electrolyte is maintained between 30 DEG C and 80 DEG C, from electrochemical oxidation of manganese (II) ions to manganese (III) ions. The method of electrochemical oxidation of manganese (II) ion to manganese (III) ion according to claim 10, wherein the electrolyte does not contain any permanganate salts. The method of claim 13, wherein the platable plastic comprises an electrochemical oxidation method from manganese (II) ion to manganese (III) ion, comprising acrylonitrile-butadiene-styrene or acrylonitrile-butadiene-styrene / polycarbonate . A method of etching a plastic part comprising contacting a plastic part with a solution comprising manganese (III) ions and an acid, wherein the manganese (III) ion forms a metastable complex, Way. 31. The method of claim 30, wherein the acid comprises sulfuric acid. 32. The method of claim 31, wherein the acid comprises from 9 to 15 moles sulfuric acid. 33. A method according to any one of claims 30 to 32, wherein the plastic part comprises ABS. 32. A method according to any one of claims 30 to 32, wherein the manganese (III) is produced in the solution by electrolytic oxidation of manganese (II). 35. The method of claim 34, wherein the electrolytic oxidation occurs at the anode in the solution, and wherein the anode comprises glassy carbon, reticulated vitreous carbon, or woven carbon fibers. delete