We continue to review some of the most important materials in heat treatment and metallurgy.
Germanium (chemical symbol: Ge)
Germanium is a hard, brittle, silvery-white (Fig. 1) semi-metal, having some properties of both metal and nonmetallic elements. Sandwiched between silicon and tin on the periodic table, germanium is a semiconductor like silicon. Naturally occurring germanium is very rare and is the 50th most abundant element on earth. Germanium ores are found in small amounts as the minerals argyrodite and germanite. Germanium is commercially produced from zinc-smelter flue dust and is also obtained from the byproducts of combustion of certain coals.
Germanium was discovered in February 1886 by German chemist Clemens A. Winkler. It was contained in an ore (today known as argyrodite, Ag8GeS6) discovered in 1885 by a miner near Freiberg, Germany. The element had been predicted by renowned chemist Dmitri Mendeleev to fill a gap in the periodic table below silicon (Si) and above Tin (Sn). Mendeleev named the undiscovered material Ekasilicon. He anticipated its atomic weight would be about 72, its density about 5.5 g/cm3 and predicted other properties of the material. His predictions of the material characteristics were amazingly accurate (Fig. 2).
Germanium played a monumental role in the development of modern computing. In one of the most important technological developments of the 20th century, physicists William Shockley, John Bardeen and Walter Brattain invented the transistor, at Bell Labs in 1947, for which they were awarded the Nobel Prize. This discovery ushered in the modern age of computers and the technology revolution that is still ongoing today.
Germanium was used in transistors until the late 1950s, when it was replaced by silicon, which is more stable at elevated temperatures. Germanium remains in use today in fiber optics, solar cells and light-emitting diodes (LEDs). The element has unique optical properties, and unlike conventional silica-based glass, it is invisible to infrared light. It is, therefore, useful as a lens in infrared equipment. It is also valuable as an alloying agent for silver, where it inhibits tarnishing.
Here are a few important facts about Germanium.
- Atomic number: 32
- Atomic weight: 72.630
- Melting point: 1211.40 K (938.25°C or 1720.85°F)
- Boiling point: 3106 K (2833°C or 5131°F)
- Density: 5.323 grams per cubic centimeter
- Phase at room temperature: Solid
- Element classification: Semi-metal
- Period number: 4
- Group number: 14
- Group name: none