Gallium is best known for melting in your hand, but its most memorable demonstration involves a drink can. Put a drop of gallium on aluminium, wait overnight, and you can tear the can apart with your fingers. It is one of the clearest illustrations of grain-boundary embrittlement you can run without a laboratory.
What you need
- A small amount of pure gallium — a few grams is plenty
- A standard aluminium drink can, empty and rinsed
- A dish of warm water to melt the gallium
- A dropper or small brush
- Gloves and eye protection
- A non-aluminium work surface
Method
1. Melt the gallium. Stand its container in warm — not boiling — water. Gallium melts at 29.76°C, so this takes a minute or two.
2. Scratch the can. Drink cans carry a thin protective oxide layer and a lacquer coating. Gently abrade a small patch with fine sandpaper or a knife so the gallium can reach bare aluminium. This step is the one people skip, and it is why the experiment sometimes appears not to work.
3. Apply the gallium. Put a drop on the abraded patch and spread it thinly. It will start to wet and spread on its own.
4. Wait. Leave it somewhere warm and undisturbed. Changes are visible within an hour or two; the full effect takes several hours to overnight.
5. Test it. Press the treated area gently. Where the gallium has penetrated, the aluminium tears like foil — and often like wet paper. Push a finger through the wall of a can that was rigid the day before.
What is actually happening
Aluminium is a polycrystalline metal: it is made of many small crystal grains bonded along their boundaries, and those boundaries are what give it strength. Liquid gallium wets aluminium and diffuses along the grain boundaries, forcing the grains apart and destroying cohesion between them.
The aluminium is not dissolved and it is not corroded in the usual sense. Each grain is essentially intact — they simply no longer hold together. This is liquid metal embrittlement, and it is a genuine engineering concern, not a party trick: it is why gallium is prohibited on aircraft in most circumstances, since aircraft are largely built from aluminium.
Safety and cleanup
- The effect is permanent and irreversible. Treat every aluminium object nearby as at risk — window frames, laptop casings, cookware, tools, ladders, bicycle frames. Work over a non-aluminium surface and wash your hands before touching anything aluminium.
- Gallium itself is non-toxic and safe to handle with normal care. Wash your hands afterwards and don't ingest it.
- Cut edges are sharp. A can that tears like foil produces edges that cut like foil. Supervise children.
- Cleanup: warm any stray gallium with a hair dryer until it flows and wipe it up with a paper towel. Never scrape it with aluminium foil or aluminium tools.
- Dispose of the treated can in general waste rather than aluminium recycling.
Recovering your gallium
Most of the gallium stays on the surface and can be warmed and collected with a dropper. It will be contaminated with aluminium and won't be as clean as it was, but for demonstrations it is perfectly reusable. Keep a small quantity set aside for can experiments rather than contaminating your main supply.
Where this fits in teaching
This demonstration covers grain structure in metals, diffusion, and the difference between a chemical reaction and a physical process — and it does so with a result students remember years later. See gallium for education for curriculum notes, or for schools and universities for quotes, purchase orders and documentation.
We stock 99.99% pure gallium in 20g, 100g, 250g and 1kg from Perth, with a Safety Data Sheet supplied on every order.