14. Inhibiting Rust Formation
Goal
To determine conditions which can inhibit rust formation.
Method
Two iron nails with no rust were coated in correction fluid and allowed to dry.
One iron nail with no rust was dipped in cooking oil, one was coated in petroleum jelly, and one was wrapped in clingfilm. These three nails were each placed in a clean, dry test tube.
One galvanized steel nail, one stainless steel screw, one painted iron nail, and one rust-free iron nail were each placed in a clean, dry test tube.
A file was used to damage the paint on a painted iron nail, and the coating of a galvanized steel nail. These two nails were each placed in a clean, dry test tube.
Distilled water was poured into the nine test tubes, to cover approximately half of each nail.
The nails and the screw were closely observed for 3 days.
Diagram
Results
The following observations were made when the starch was added to each of the glasses and the contents were stirred.
| Material and Coating | Observations after 3 days |
|---|---|
| Steel | A considerable amount of rust was observed on the nail. |
| Steel coated in cooking oil | Small amounts of rust were observed where the oil had not adhered well to the surface of the nail. |
| Steel wrapped in cling film | Mainly rust free, but pockets of rust could be observed where water had seeped into the cling film wrapping. |
| Painted steel | A small amount of rust was visible where the paint had cracked. |
| Damaged painted steel | Considerable amounts of rust could be observed where the steel was exposed to the water. |
| Steel coated in petroleum jelly | No rust was observed. |
| Galvanized steel | No rust was observed. |
| Damaged galvanized steel | No rust was observed. |
| Stainless steel | No rust was observed. |
The photo shows all the nails and screw at the end of the observation period.
Conclusion
Rust formed wherever steel was exposed to the water. This included the uncoated nail, and also those parts of the oil-coated nail, cling film wrapped nail, and painted nail which were exposed to the water.
The petroleum jelly coating prevented water from reaching the nail. The galvanized steel nails (even when the coating was damaged) and the stainless-steel nail did not rust, despite being exposed to the water.