We continue to review some of the most important materials in heat treatment and metallurgy.
Barium (chemical symbol: Ba)
Barium is a soft, silvery white metal with a gold tinge (Fig. 1) that has a high chemical reactivity and exists in nature only in combination with other elements. It readily combines with other elements such as sulfur, carbon and oxygen to form barium compounds. Barium has several curious properties. For example, barium sulfate (aka barite) rocks will luminesce when exposed to light and will glow in the dark for up to six years if heated in the presence of charcoal. Known as Bologna stones, barite rocks were first discovered near Bologna, Italy, in 1603 and were thought to have mystic properties by alchemists of the day.
Barium was first isolated and identified using electrolysis in 1808 by renowned Cornish chemist and inventor Sir Humphry Davy at the Royal Institution in London. Davy is best known for founding the field of electrochemistry and for his discoveries of various other elements, including potassium, sodium, calcium and magnesium, to name a few. He investigated nitrous oxide and gave it the name "laughing gas," because of the way it made him feel when inhaled.
Pure barium does not have many everyday uses due to its high level of reactivity with oxygen and other elements. Barium’s affinity for oxygen does make it useful as a getter in vacuum tubes to remove trace amounts of gas contaminants.
Barium compounds are very common, and its ability to combine with so many other elements gives it a wide range of uses. Barium nitrate burns a vibrant green and is used in fireworks (Fig. 2) and signal flares. Barium peroxide forms hydrogen peroxide when combined with water and is used as a bleaching agent that only becomes active when wet. Barium chloride is used as a water softener. Barium oxide readily absorbs moisture and makes an excellent desiccant. Barium titanate (a compound of barium and titanium) is used as a dielectric material in capacitors. Barium ferrite is used to make magnets. Barium sulfate is used as a brightening agent in paint and printer paper and in manufacturing glass and rubber. Barium carbonate is used as a rat poison.
In metallurgy, barium is used in the Hoopes process of aluminum refining, which is a technique used to produce extremely high-purity (99.99%) aluminum by using electrolysis of molten aluminium with a sodium, barium and aluminum-fluoride electrolyte.
Here are a few important facts about Barium.
- Atomic number: 56
- Atomic weight: 137.327
- Melting point: 1000 K (727°C or 1341°F)
- Boiling point: 2170 K (1897°C or 3447°F)
- Density: 3.62 grams per cubic centimeter
- Phase at room temperature: Solid
- Element classification: Metal
- Period number: 6
- Group number: 2
- Group name: Alkaline-earth metal