Gallium

Gallium is a chemical element with symbol Ga and atomic number 31.

Properties

Chemical

Gallium is attacked by acids and free halogens, but does not react with air or water at room temperature, only at high temperatures, producing gallium(III) oxide Ga₂O₃. If Ga₂O₃ is reduced with elemental gallium in vacuum at 500-700 °C, it will yield the dark brown gallium(I) oxide, Ga₂O.

Ga₂O₃ + 4 Ga → 3 Ga₂O

Gallium(I) oxide is a strong reducing agent, capable of reducing sulfuric acid to hydrogen sulfide.

Gallium attacks most other metals by diffusing into their metal lattice. Aluminium is highly susceptible, as well as zinc, aluminium-zinc alloys, certain steel grades, making them very brittle.

Physical

Gallium is a soft silvery metal, brittle at low temperatures. If it is held in the human hand long enough, gallium will melt, since its melting point is 29.76 °C. Gallium expands by 3.1% when it solidifies, and therefore storage in either glass or metal containers should be avoided. Liquid gallium has a strong tendency to supercool below its melting point/freezing point. Unlike mercury, liquid gallium wets glass and skin, making it mechanically more difficult to handle. For this reason, as well as the metal contamination and freezing-expansion problems, samples of gallium metal are usually supplied in polyethylene packets within other containers.

Availability

LED's contain a minute amount of gallium nitride, but the quantity is too small to be of importance. Certain low melting alloys contain gallium.

The best source of metallic gallium is GalliumSource, that sells gallium samples, a 100 g sample costs around 65$, though the price does not include shipping. For international shipping, the price is higher and the shipping is included in the price.

Preparation

Gallium can be prepared by reducing its halides.

Projects

• Inducing embrittlement in susceptible metals, such as aluminium
• Gallium nitride synthesis
• Gallium spoon prank
• Gallium beating heart
• Hydrogen generation

Handling

Safety

Pure gallium has little toxicity, but its tendency to wet most materials can be frustrating, so gloves should be worn when handling the pure metal, especially since it will melt in the hand if held too long. Some of its compounds have been shown to cause renal problems in tested animals. Bulk gallium nitride has been shown to be non-toxic and even bio-compatible.

Storage

Because gallium tends to expand when it solidifies, it's best stored in thick polyethylene bottles or if it's a small sample, in top lid boxes.

Disposal

Gallium is best recycled, when possible.

References

Relevant Sciencemadness threads

• Purifying Gallium