Is your favorite garden tool getting rusty? Are you going to bury a metal post in the ground and want to know how to protect it from rusting away in the wet ground? This instructable will give you solutions to these problems!
When iron gets wet in the presence of oxygen, it forms iron oxide also known as rust. This can be written as a chemical reaction like this:
Fe (s) + O2 (g) --> Fe2O3 (s)
During this reaction, what is happening is the oxygen gas is taking electrons from the iron. Before the reaction, the iron atom has a charge of zero because it an equal number of protons, which have a charge of positive one, and electrons, which have a charge of negative one. After the reaction, the iron ion has a charge of +3 and the oxygen ion has a charge of -2.
To prevent iron from rusting, you can either coat the iron with something like another metal or have another metal nearby that is easier to remove electrons from than the original piece of metal.
Step 1: Figuring Out What Metal Will Coat Which Other Metal
So how do you figure out which metal will coat which other metal? I have an iron nail and an iron horseshoe in my pictures.
You could do by researching the answer, but why not do a series of experiments? After all, isn't that more fun!
To do this experiment you will need:
- a corrosive solution such as salt water or vinegar
- sample of several metals such as aluminum, zinc, iron, gold, silver, nickel, copper
Think about how you can systematically complete this investigation so you are sure that you will generate clear results.
- How many metals do you want to put in each solution at a time?
- How long do you want to leave the samples before you record observations?
- How large a piece of metal do you want to use?
- How will you clean each piece before putting in your solution?
- How strong a corrosive solution do you want to use?
These are all questions you want to answer before starting the experiment. I could give you the answer here, but where is the fun in that!
Step 2: Cleaning Your Metal Object to Be Coated
Some objects will be very very dirty, some will be fairly clean so how much cleaning you need to do will vary depending on the condition of the object before you start. Here are options for cleaning your metal object:
- Remove the bulk of the dirt and rust with a stiff wire brush or steel wool. Steel wool is available in several different strand thicknesses, start with the largest thickness and work your way down to the fine one.
- Put the object in a bucket of kitty litter, then put the bucket on an oscillating object like an orbital sander to shake up the kitty litter and remove debris from the object by abrading the rust.
- Dip into concentrated muriatic acid. This is very corrosive! Make sure you are working in a well ventilated area with a respirator, wear chemical splash goggles, and make sure you are wearing appropriate chemical gloves. The used acid needs to be neutralized until it increases to a pH of 7 to be disposed of safely, you can neutralize it with baking soda. This is serious stuff, but it is very effective at removing rust. Be careful, and have another person nearby in case you have trouble and need assistance. Its hazardous, but very quick and effective.
- Rinse the object well with water to remove any debris and/or acid and/or steel wool particles that remain after the previous steps.
- Rinse the object with acetone, this also is a hazardous liquid, use this in a well ventilated with a respirator and appropriate chemical gloves. Make sure you dispose it properly, disposal rules are different for different locations so check your local rules. I reuse my acetone for this so I just keep a "used" bottle for rinsing my cleaned metal.
Step 3: Setting Up Your Electroplating System
Your object is now nice and clean, its time for the main event -- electroplating!
To assemble an electroplating system, you need two metal objects, a container, an electrolyte (like salt water), some wire, and a power supply.
In the example in the picture there is a bucket of salt water, a horseshoe that has been cleaned, a wire the goes between the horseshoe and one end of the battery, and a wire that goes between a chunk of zinc and the other end of the battery. A long strip at the end of the wire has been stripped of its insulation so there is a long section of good contact between the horseshoe and the exposed copper wire. I wrapped the wire around the tip of the horseshoe several times to hold that wire securely in place. If I wanted to coat the whole horseshoe, I would periodically take it out of the bath and shift the wire wrap farther down the horseshoe. I used a 9 volt battery to power my electroplating system.
When you are electroplating, the two metals objects are connected to the battery but not each other. The part of the metal you want coated needs to be completely submerged. For this trial, I was resting the horseshoe on the side of the bucket so that only the tip of the horseshoe would be coated with zinc.
The solution, called the electrolyte, contains ions which are atoms with an electrical charge. When you use salt water, the ions are positively charged sodium ions and negatively charged chlorine atoms that form when sodium chloride is dissolved in water. The two metal objects are called electrodes. The electrodes and electrolyte choices make a difference in how well the electroplating system works. These electrodes and electrolyte make a complete circuit with the battery so energy will flow from the battery through one of the electrodes to the electrolyte taking some of the metal ions from that electrode to the other electrode where some of those metals ions are deposited and then back to the battery to repeat the cycle. The electrode that is connected to the positive end called a positive terminal of your battery is the metal that you are using to plate your object, so the piece of zinc in my zinc plated iron horseshoe example. The electrode that is connected to the negative terminal of the battery is the object you want to plate so the iron horseshoe in my example. I used sodium chloride because I had lots of cheap sodium chloride around, but to get an even better coating you can match the metal ion in your electrolyte solution with the metal you want to coat. For example, if you are coating something with copper you can use a copper sulfate solution for your electrolyte. Or for my example I could have used a zinc sulfate solution instead of sodium chloride. Just remember to research how to properly dispose of your left over solution according to the disposal rules in your area when you finish with your experiment.
Step 4: Coating Your Metal Object
Now that your electroplating system is assembled, let it run and thoroughly coat the metal object you are trying to protect from corrosion. Pay attention to the time you keep it in the system, and keep track of how you cleaned your object. Both of these will impact the ability of the electroplated metal to stick to your object. The cleaning with acetone before starting is particularly important so it removed any oily residue (like the oil the object picks up from your skin as you handle it) that will block the electroplated metal from really adhering well to the object.
Step 5: Investigating Ways to Optimize the Metal Coating
So you tried it once, how did it work? Now its time to fine tune your process to get the thickest, most durable coating you can without taking too long to complete the electroplating or using too much of the coating metal. So what variables can you adjust?
How about the surface area of the metal you are coating onto your object? The separation of the two items in the electroplating bath? The time you run the electroplating bath? The amount of energy you provide to system with your batteries?
Once you do your first trial keep notes of how you electroplated each additional object so you find the ideal choices for your coatings. Good luck with your endeavor, you are on your way to preventing corrosion!