Introduction: (Initial Observation)
Iron and brass are two widely used and easily available metals used in manufacturing parts. Although these two metals are inexpensive, easy to form and strong, they both rust and corrode in the air. To prevent rusting, they are often covered with oil, plastic, paint or a layer of other metals that don’t rust such as chromium.
Covering metals with a layer of another metal is called plating and when it is done using the electricity, it is called electroplating. Of course electroplating is not the only way of coating one metal with another metal. Other well known methods are vacuum plating and chemical plating orelectroless plating.
The electroplating industry is a $12 billion industry, however electroplating can also be a small business or a hobby.
In this project we will study electroplating principals and practical applications.
Find out about electroplating. Read books, magazines or ask professionals who might know in order to learn electroplating techniques. Keep track of where you got your information from.
What is Electroplating?
Electroplating is one kind of surface finishing. There are many other kinds. Everyone has seen and handled electroplated objects, even if they didn’t know it. Examples include kitchen and bathroom faucets, inexpensive jewelry and the trim on some automobiles. There are thousands of examples. In fact, it is certain that nearly every piece of metal you have ever seen has been through some kind of surface finishing process. There are three basic reasons for surface finishing: to improve appearance, to slow or prevent corrosion (rust) and to increase strength and resistance to wear (in the case of “engineering” finishes). An object may be processed for any or all of these reasons.
The term electroplating means the coating of an object with a thin layer of metal by use of electricity. The metals most often used are gold, silver, chromium, copper, nickel, tin and zinc, but many others are also used . The object to be plated is usually a different metal, but can be the same metal or a non-metal, such as a plastic grille for an automobile.
Electroplating usually takes place in a “tank” of solution containing the metal to be deposited on an object. This metal is in a dissolved form called ions. An ion is an atom that has lost or gained one or more electrons and is thus electrically charged. You cannot see ions, but the solution may show a certain color; a nickel solution, for example, is typically emerald green. The deposited metal, however, will be gray or silver in appearance.
When certain metallic chemicals dissolve in water, the metal atoms of these chemicals are freed to move about, but lose one or more electrons (negative charges) and, as a result, are positively charged. The object to be plated is negatively charged and attracts the positive metal ions, which then coat the object to be plated and regain the lost electrons to become metal again.
A familiar example of this process is the experiment often performed in which a key is plated with copper. The key (called the cathode) is connected to the negative terminal of a battery and is placed in a solution of vinegar, a weak acid. The positive terminal of the battery is connected to a piece of copper (called the anode–and often just a copper wire), which is placed in the solution. The acid slowly dissolves the wire, making copper ions that are then attracted to the key, regaining their lost electrons and becoming copper metal again, but now in the form of a thin coating on the key. The battery forces all this to happen and prevents the deposited copper from re-dissolving.
Now look at the illustration. Positively charged copper ions are free in the solution, but are being attracted by the negatively charged key. As the ions contact the key, they regain their lost electrons and become copper metal and stick to the key wherever they touched it. This is the basic process of electroplating, and all forms of it work the same way.
Other Common Finishing Processes
Electrical and chemical processes are not the only ways to coat an object. Another important process is called vapor deposition or vacuum coating. In this process, the metal to be deposited is converted into a vapor that is allowed to condense on the object to be coated. Many beautiful finishes can be obtained by this process, which is carried out in a vacuum chamber.
Another increasingly important surface finishing process is powder coating. It depends on the fact that opposite charges attract, just as in electroplating. The object to be coated is electrically charged and is sprayed with a non-metallic powder that sticks to it. The object is then passed through an oven where the powder particles melt and run together to make a smooth finish. Articles commonly coated in this way include lawn mower frames, sports equipment, playground equipment, lawn furniture and the insides of refrigerators, washing machines and dryers.
Some metals including aluminum can not be coated by electroplating method. In order to protect aluminum from rust, we usually anodize it. Anodizing process involves producing a very thin, invisible layer of the oxide on the aluminum, which protects it from the kinds of corrosion that affect aluminum, such as salt air from the ocean. The oxide is a chemical combination of aluminum and oxygen. Anodized aluminum can be dyed to produce any desired color.
Electroplating uses a small electric current to drive atoms of one metal from one object onto the surface of another.
(An atom is the smallest amount of an element — the basic building blocks of all matter. An atom is the smallest amount of stuff you can have, and still be able to call it an element.)
The process was discovered by physicist Michael Faraday, who did most of his work dealing with the connections between electricity and magnetism.
To “plate” one material onto another, you need to have a setup like the top diagram. The anode is the metal you want to plate onto the cathode. The electrolyte is a liquid that conducts electricity and that will dissolve the anode. It will also contain dissolved ions of the anode metal in it. (An ion is any atom, or group of atoms, with an electrical charge, either positive or negative.) The key to this process is the battery. It supplies the energy needed for the atoms in the anode to dissolve into the electrolyte, and eventually “stick” to the cathode.
If you let enough electrical current pass through the solution, you will get a layer of anode metal on the cathode, with the anode dissolving into the electrolyte. The thickness of the layer can be precisely controlled by varying the amount of current that passes through the electrolyte.
Quick Reference Electroplating Guide
|GOLD||140ºF||6V||30 sec||24K gold|
|RHODIUM||80 – 100ºF||4V||20 – 30 sec||14K or platinum|
|COPPER||100ºF||6V||30 + sec||copper|
|NICKEL||70ºF||2V||3 – 4 min||nickel|
|SILVER||70ºF||2V||30 + sec||silver|
The purpose of this project is to learn about the principals of electroplating and it’s practical applications.
You may have hundreds of other questions about electroplating that may become a base for your project. Following are some sample questions:
- What is the effect of temperature in nickel plating?
- What metals can be plated on what other metals?
- What is the best concentration for plating bath?
- What bath additives can contribute to the sine of plated surface?
- What is the effect of pH on a specific plating (Nickel plating)?
Depending on the question of your project you may identify variables in different ways. For our purpose that is learning the principals, we do not have to identify variables. However if you select any of the above questions then you define variables like this:
Variables for first question:
In this project temperature of the plating bath is an independent variable. The weight of metal deposited on cathode is the dependent variable.
Even though we are not going to study any specific variable at this time, we considered that the following factors could affect the deposition of Copper metal on the cathode.
- Molarity/ Concentration of Solution
- Quantity of Solution
- Size of Electrodes
- Distance between the electrodes
- The surface of the electrodes
Propose a hypothesis based on the purpose and question that you select.
For example a possible hypothesis for the first question is:
I hypothesize that as the temperature increases the electrolysis will take place faster and more efficiently because particles move faster when there is more heat. This is because of the kinetic theory, the more heat, the more energy so the particles move faster.
For the principals of electroplating also you may have a hypothesis like this:
My hypothesis is that anode must always be of the type of plating metal. For example for copper plating, anode must be copper. The electrolyte must contain enough ions of plating metal. Also I think that the electrolyte does not need to be acidic in order to dissolve more anode, because as metallic ions are attracted by the cathode, they will be replaced by new ions separated from anode.
Anode: Metal or conductor attached to the positive electricity
Cathode: Metal or conductor attached to the negative electricity
The purpose of this experiment is to see electroplating in action and successfully complete an electroplating test. After being able to successfully perform an electroplating experiment, you will be ready to test the effect of any specific variable such as pH or temperature or anything else related to the question that you choose.
At the end of the experiment you should be able to:
- construct an electroplating device.
- describe chemical changes that involve the transfer of electrons.
- describe the procedures used and the reactions occurring during the electroplating of a metal.
- 250 ml beaker or any similar cylindrical plastic container
- 6 volt battery (known as lantern battery) or a DC power supply
- Alligator Clips
- Copper sulfate solution (CuSO4)
- (Copper sulfate can be purchased from hardware stores and pool suppliers.)
- Copper Strip (as copper electrode or anode)
- Spoon, Nail, Coin
- A variety of other metals (optional)
- (optional) Silver nitrate, sulfuric acid, caustic soda
General Safety Considerations
Wear protective glasses and an apron at all times. Avoid skin contact with solids and solutions. Dispose of the solutions and wash your hands as soon as you finish your experiment.
You will perform an electroplating experiment. In this activity, the reversibility of electrochemistry will be seen as a current causes a chemical reaction to take place. The reaction will occur when a copper strip and a spoon are placed in copper sulfate solution. Both the copper strip and spoon will be attached to wires which are hooked to the positive and negative electrodes of a battery. The current will result in the movement of copper ions.
Preparation of Plating Solution: Dissolve 250 g of CuSO4•5H2O in 500 mL distilled water, (Optional/ Danger) add 50 mL of 3 M sulfuric acid, H2SO4, and dilute to 1 L.
Preparation of 3 M sodium hydroxide, NaOH: (Optional/ Danger) While stirring and cooling, dissolve 120 g sodium hydroxide into 700 mL of distilled water. Dilute to one liter when cool.
Preparation of 3 M sulfuric acid, H2SO4 (for 12 stations): (Optional/ Danger) While stirring and cooling, slowly add 160 mL of concentrated sulfuric acid, H2SO4, to 700 mL of distilled water. Dilute to one liter when cool.
Part I: Cleaning
1. Clean the the nail being plated and copper electrode by rubbing with fine steel wool. Wash them with a detergent solution and rinse both with tap water.
2. Attach a bare copper wire or an alligator clip to the nail. The wire serves as a “handle” to remove the nail from the cleaning solutions.
3. Soak the nail and copper electrode for a few minutes in 30 mL of 3 M sodium hydroxide solution (that is 120 grams per liter), NaOH. (Caution: Avoid contact of skin with sodium hydroxide.) Remove with tweezers and rinse in distilled water. This process is called degreasing. Skip this if you don’t have caustic soda, instead wash it with dish washing detergent.
4. Soak the nail and copper electrode for a few minutes in 30 mL of 3 M sulfuric acid, H2SO4. (Caution: Avoid contact of skin with sulfuric acid.) Remove with tweezers and rinse with distilled water. Skip this if you don’t have sulfuric acid, instead wash it with dish washing detergent.
5. Pour 150ml of the copper sulfate solution in a 250 ml beaker that is being used as your electroplating bath.
Part II: Electroplating
1. Place a 1 cm x 10 cm copper strip into the beaker. Bend the strip to fit over the top of the beaker .
2. Support the nail in the solution by wrapping the copper wire around a small glass rod or a pencil. Rest the rod on top of the beaker.
3. Hook up the battery. The nail should be wired directly to the negative electrode. The copper electrode should be wired to the positive electrode. Caution: the nail and the copper strip should not touch.
4. Double check all the connections
5. Allow the current to flow for about five minutes.
6. Disconnect the alligator clips and remove the nail.
7. Rinse with distilled water and blot dry with a paper towel.
The Science Behind the Activity
Electroplating is an example of an oxidation-reduction reaction. Copper metal is taken out of solution and plates onto the spoon. Concepts students should comprehend are that oxidation is a loss of electrons, reduction a gain of electrons. The battery supplied the extra electrons.
The (Cu) ions in the solution, which have a charge of 2+, combine with the extra electrons on the object to be plated. The copper strip becomes oxidized (loses electrons) and the spoon becomes reduced (gains electrons).
Cu++ + 2e- ==> Cu
The loss of Cu 2+ ions in solution (those that are being plated out onto the spoon) can be observed, since the solution will begin to lose its blue color over time. The blue tint is due to the copper ions in solution, so as they are taken out of solution and plated onto the spoon, the solution loses its blue tinge.
You could experiment with other metals and solutions. A solution of silver nitrate may be used instead of copper. Try different metals and see the results (try using zinc, copper, stainless steel, lead, etc.)
Avoid ingestion of copper sulfate and silver nitrate solution.
Materials and Equipment:
List of material can be extracted from the experiment section.
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
The result of copper plating on a nail was very bad. A lot of copper has deposited on iron but rinsing it under water easily removes all the copper. One thing that I noticed is that even without any electricity, copper will deposit on Iron with an identical result. Also I noticed that while electric current is flowing, that side of the nail that is towards the anode gets more and faster copper deposits.
I decided to change the temperature, reduce the voltage or change the concentration of the copper sulfate to see what will be the result.
To reduce the voltage, I replaced the 6 volt battery with a 1.5 volts battery. The process was slower, but the final result was the same. Diluting the solution and warming it up also did not help.
Finally I decided to search for the cause of the problem and found the answer on finishing.com website.
The answer is that copper is more noble than iron and will, as you saw, plate without any current applied. This is called an “immersion deposit” and it has almost no adhesion.
You need to electroplate an initial layer from a nickel strike or a cyanide copper, before you will be able to use the copper sulfate bath. Even then, you probably won’t get good, bright, plating without proprietary additives.
So I repeated my test with a quarter (coin) that already in nickel. It resulted a good and strong copper deposit.
Summary of Results:
I observed that passing a direct electric current through an aqueous copper sulfate solution results in copper atoms being dissolved into the solution from the anode while positive copper ions (cations) being discharged at the cathode. Normally anions are discharged at the anode
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.