Steel is a great metal for building and construction as it is strong and able to be shaped. However, when moisture, oxygen and pollutants in the air come in contact with steel, the chemical reaction causes corrosion or 'rusting'. Rust occurs when the crystal bonds in the metal break down and continual rusting will eventually completely weaken the steel.
Fortunately, other metals such as chromium and magnesium can be alloyed with the steel to help make it rust-resistant. Also, special protective coatings on steel can stop rusting.
When the metal zinc is coated on the surface of steel (by dipping the steel in a hot liquid solution of zinc - a process called 'galvanising') the zinc forms a special layer of zinc oxide which protects the steel underneath. Zinc is known as 'the great protector'. No doubt you have seen a backyard shed, fence or roof made from a galvanised steel products such as Zincalume®, Colourbond® or Galvalume®.
This activity compares unprotected (or damaged) steel products with treated steel products in a range of fake 'weather conditions.' You will see how rust forms and what it does to certain metals.
| 1) | Working in groups, make up the wet environments. These are your various 'weather conditions'. Only half-fill the container so that there is some air left inside. The rusting process needs both moisture and oxygen. |
| 2) | Place a similar quantity of each product in each of the liquids. Label clearly. |
| 3) | Store all the samples in the same light/dark and temperature conditions. |
| 4) | Observe what happens to your samples over the next 3-5 days. |
| 5) | Record your observations using a table like the one below. Look for changes such as - in colour, breaking down of the product, or production of a smell. |
Sample: Iron Filings - Effects of 'Weather Conditions'
| Day | Tap Water | Distilled Water | Salt Water | Bleach | Vinegar |
| 1 | Water turned orange | ||||
| 2 | Water bright orange Metallic smell Few filings left |
| 1) | Did your product react in some 'weather conditions' more than in others? Why do you think this is? |
| 2) | Were some products more sensitive (did they react or change more) than others in particular conditions? |
| 3) | Do these products have something in common? (colour, smell, etc). |
| 4) | What parts of the Olympic venues would be the most susceptible to damage? |
| 5) | What could happen to the venues at the 2008 Olympics if they were made of non-galvanised steel? |
| 1) | Make some scratches on the products that were not affected. Repeat some tests and note any differences or changes that did not occur before. |
| 2) | What does this tell you about how the product is protected? (For example, does the protection work like a coating as if it was painted on, or is the protection throughout the product?) |
| 3) | Would an environment that is hotter or brighter make any difference? How would you test this? |
| 4) | Try filling the container up completely with the liquids so that no air is in it. What do you think might happen? |