Patent Application
20110253556
This application is one of the five related co-pending U.S. patent applications listed below. All listed applications have the same assignee. The disclosure of each of the listed applications is incorporated by reference into all the other listed applications.
1. Technical Field
The present disclosure relates to a solution system for electrolytically removing titanium carbide coating and a related method.
2. Description of Related Art
Hard ceramic coatings, such as titanium carbide, are widely attached on surfaces of machining tools and die core-pins. These coatings, however, can fail locally during use or manufacture. Often, when such coatings fail, the entire component which they are applied is discarded at considerable cost even if the underlying substrate shows no damage. For this reason, the ability to recycle the underlying substrate by removing a failed coating is economically preferable.
Titanium carbide coating resists wear, abrasion, oxidation, and corrosion. When manufacturing such coating, the content of carbon increases with the increasing thickness of the coating to improve the hardness and adjust color of the coating. Electrolytic removal of such coating is often carried out using an electrical current density of higher than 12A/dm2 for a long period of time. However, the underlying substrate may be corroded and this process is very costly.
Therefore, there is room for improvement within the art.
The present disclosure relates to a solution system and a related method for electrolytically removing titanium carbide coatings formed on the surfaces of substrates. The substrate may be metal, such as ferric-based alloy.
The solution system includes a firs electrolyte solution for a first electrolysis step and a second electrolyte solution for a second electrolysis step.
The first electrolyte solution may be an aqueous solution containing a first alkali and a first accelerant.
The first alkali may be soluble alkali metal hydroxides, such as, sodium hydroxide, or potassium hydroxide, or a combination thereof. The concentration of the first alkali selected may be about 2-80 g/L, and in this exemplary embodiment is about 5-50 g/L. The first alkali makes the solution electrically conductive and providing an alkali condition acid in dissolution of the in the titanium carbide coatings into the solution.
The first accelerant is a complexant capable of complexing with titanium ions. The first accelerant may be sodium potassium tartrate, sodium gluconate, sodium citrate, or ethylenediaminetetraacetic acid (EDTA), or a combination thereof. The concentration of the first accelerant selected may be about 5-100 g/L and in this exemplary embodiment is about 5-40 g/L. The first accelerant can combine with the titanium ions dissolved in the solution to form coordination compounds and facilitate a continuing dissolution of the titanium ions of the titanium carbide coating.
The first electrolyte solution may be prepared by dissolving the first alkali and the first accelerant in water.
The second electrolyte solution may be an aqueous solution containing a second alkali, a second accelerant, and an auxiliary agent.
The second alkali may be soluble alkali metal hydroxide, such as, sodium hydroxide, or potassium hydroxide, or a combination thereof. The concentration of the second alkali selected may be about 50-300 g/L, and in this exemplary embodiment is about 120-180 g/L. The second alkali may perform a similar effect with the first alkali of the first electrolyte solution.
The second accelerant is a complexant capable of complexing with titanium ions. The second accelerant may be sodium potassium tartrate, sodium gluconate, sodium citrate, or EDTA, or a combination thereof. The concentration of the second accelerant selected may be about 5-100 g/L, and in this exemplary embodiment is about 5-40 g/L. The second accelerant may perform a similar effect with the first accelerant of the first electrolyte solution.
The auxiliary agent may be generic alkylol amine capable of combine with titanium ion. The auxiliary agent may be ethanolamine, diethanolamine, or triethanolamine, or a combination thereof, and preferably triethavolamine. The concentration of the auxiliary agent selected may be about 10-60 g/L, and in this exemplary embodiment is about 18-40 g/L. The auxiliary agent may absorb small solid impurities produced during electrolysis, preventing the impurities from adhering on the substrate.
The second electrolyte solution may be prepared by dissolving the second alkali, second accelerant, and auxiliary agent in water.
The method for electrolytically removing the titanium carbide coating formed on the substrate may include the following steps.
The substrate combined with the coating may be immersed in the first electrolyte solution and processed by a first electrolysis step using the substrate as the anode. The temperature of the first electrolyte solution during the first electrolysis step is maintained between about 50° C. and about 95° C., and in this exemplary embodiment is between about 60° C. and about 80° C. Stainless steel or carbon material may be used as the cathode. The anodic current density is about 1-10A/dm2, and in this exemplary embodiment is about 4-7A/dm2. The first electrolysis step takes about 3-8 minutes. After the first electrolysis step, the exterior portion of the coating having a high content of carbide may be removed. Then, the substrate is rinsed with water and then dried.
The substrate combined with the coating may be immersed in the second electrolyte solution and processed by a second electrolysis step using the substrate as the anode. The temperature of the second electrolyte solution during the second electrolysis step is maintained between about 50° C. and about 95° C., and in this exemplary embodiment is between about 60° C. and about 80° C. Stainless steel or a carbon material may be used as the cathode. The anodic current density is about 1-10A/dm2, and in this exemplary embodiment is about 4-7A/dm2. The second electrolysis step takes about 3-8 minutes. After the second electrolysis step, the remainder titanium carbide coating can be completely removed from the substrate.
After the second electrolysis step, the substrate may be rinsed using an aqueous solution containing about 5 wt % sulphuric acid, and then rinsed with water and dried. The coating can be effectively removed from the substrate and the underlying substrate is free from damage.
Experimental examples of the present disclosure following.
The first electrolyte solution and the second electrolyte solution were prepared. The first electrolyte solution was an aqueous containing 5 g/L sodium hydroxide and 10 g/L EDTA. The second electrolyte solution was an aqueous containing 150 g/L sodium hydroxide, 20 g/L sodium potassium tartrate, and 33 g/L triethanolamine.
Samples of stainless steel substrate having a titanium carbide coating were provided. The coatings had a thickness of about 2 μm. The exterior layer of the coatings was removed by a first electrolysis step in the first electrolyte solution using the substrate as the anode, and using an anodic current density of about 4A/dm2 for about 4 minutes. A piece of carbon was used as the cathode. The solution was maintained at a temperature of about 60° C. Then, the samples were taken out of the solution and rinsed with water.
The remainder of the coatings was completely removed by a second electrolysis step in the second electrolyte solution using the substrate as the anode, and using an anodic current density of about 5A/dm2 for about 4 minutes. A piece of carbon was used as the cathode. The second electrolyte solution was maintained at a temperature of about 80° C. Then, the samples were taken out of the solution and were rinsed with acidic solution and water.
Unlike the example 1, the first electrolyte solution was an aqueous containing 20 g/L sodium hydroxide and 20 g/L EDTA. The second electrolyte solution was an aqueous containing 75 g/L sodium hydroxide, 20 g/L sodium citrate, and 28.6 g/L triethanolamine. Except the above difference, the remaining experiment conditions of example 2 were respectively same with example 1.
The first electrolyte solution and the second electrolyte solution were prepared. The first electrolyte solution was an aqueous containing 10 g/L sodium hydroxide and 10 g/L sodium gluconate. The second electrolyte solution was an aqueous containing 100 g/L sodium hydroxide, 10 g/L sodium potassium tartrate, 5 g/L sodium gluconate, and 16.3 g/L triethanolamine.
Samples of stainless steel substrate having a titanium carbide coating were provided. The coatings had a thickness of about 2 μm. The exterior layer of the coatings was partially removed by a first electrolysis step in the first electrolyte solution using the substrate as the anode, and using an anodic current density of about 3A/dm2 for about 5 minutes. A piece of carbon was used as the cathode. The solution was maintained at a temperature of about 65° C. Then, the samples were taken out of the solution and rinsed with water.
The remainder of the coatings was completely removed by a second electrolysis step in the second electrolyte solution using the substrate as the anode, and using an anodic current density of about 6A/dm2 for about 5 minutes. A piece of carbon was used as the cathode. The second electrolyte solution was maintained at a temperature of about 80° C. Then, the samples were taken out of the solution and were dried after being rinsed with water.
The samples processed in the examples 1-3 were inspected by X-ray diffraction (X-RD). No titanium was detected on the samples. Accordingly, the coatings were effectively and completely removed from the underlying substrates. Furthermore, the processed samples were scanned using an electron microscope. The scanning indicated no corrosion found on the underlying substrates.
It should be understood, that the first electrolyte solution or the second electrolyte solution may be solely used as the electrolyte for electrolytically removing the titanium carbide coating by one electrolysis step.
It is believed that the present embodiment and its advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the disclosure or sacrificing all of its advantages, the examples hereinbefore described merely being preferred or exemplary embodiment of the disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201010151339.3 | Apr 2010 | CN | national |
