A metal with a reputation tainted by underground nuclear testing!
Strontium is a soft, silvery, reactive metal. On contact with water, strontium enters into a reaction, with the formation of strontium hydroxide and hydrogen. If the metal is left in the air, the surface quickly acquires a yellowy color from the formation of strontium oxide. Finely dispersed strontium self-combusts in air.
How strontium was discovered
Strontium is not encountered in nature in free form, but is present in over 40 different minerals. Strontium was named after the Scottish village of Strontian, where a new ore was discovered in lead mines located nearby. In 1790, the local doctor Adair Crawford and his chemist colleague, William Cruickshank from Woolwich, discovered a new mineral (strontianite) in witherite (a barium carbonate mineral), and published an article about their findings.
The physician and mineral collector Friedrich Gabriel Sulzer, together with Johann Friedrich Blumenbach, analyzed the mineral from Strontian and called it strontianite. They also concluded that this mineral differed from witherite, and contained a new earth (neue Grunderde). The chemist Thomas Charles Hope confirmed that strontianite contained a previously unknown element, and noted that this element turned flames red.
In 1799, another mineral containing strontium was discovered in Gloucestershire, England, where it was used to sprinkle decorative sand paths in backyards and gardens. This mineral contained strontium sulfate and was known as celestine. In 1808, Sir Humphrey Davy first isolated strontium in pure form through the electrolysis of strontium chloride and mercury oxide, and announced this breakthrough to the Royal Society on the 30th of June 1808.
Application of strontium
In the manufacture of fireworks, strontium carbonate, nitrate and perchlorate are used to color flames a crimson-red color. An alloy of magnesium and strontium has powerful pyrophoric qualities and finds application in fireworks for incendiary and flaring compounds, Strontium is added to copper and several of its alloys and to lead alloy batteries, and is used for the desulfurization of cast iron, copper and steel, and also for the reduction of uranium.
Alloys of strontium with tin and lead are used for casting conductors of accumulator batteries. Alloys of strontium and cadmium are used for the anodes of battery cells. Hard ferrites of strontium are widely used as materials for the manufacture of permanent magnets.
Strontium uranate plays an important role in producing hydrogen (the strontium-uranate cycle, Los Alamos, USA) by the thermochemical method (atomic hydrogen energy), and methods are being developed for uranium fission in strontium urinate, to produce heat in the breakdown of water into hydrogen and oxygen.
Strontium oxide is used as a component in superconductive ceramics. In the solid solution of the oxides of other alkali earth metals – barium and calcium (BaO, CaO) – it is used as an active layer of indirectly heated cathodes in vacuum electronic devices. Strontium fluoride is used as a component of solid-state fluorine batteries with a high energy capacity and energy density.
Strontium-89 chloride, which has a half-life of 50.55 days, is used as an antitumor drug. Strontium chloride is sometimes used in toothpastes for sensitive teeth – it protects the surface of teeth exposed by gum recession. The human body absorbs strontium just as well as calcium, as these two elements are very chemically similar. Dietary additives containing strontium are sold as “bone restoratives”, and studies by the New York College of Dental Sciences showed that the use of strontium in osteoblasts (bone tissue cells) caused an increase in their growth.
Ordinary strontium is not radioactive, but it is often associated with the radioactive isotope Strontium-90, which was formed in underground nuclear explosions conducted in the mid-20th century, and became the main source of pollution. Strontium-90 is a very powerful source of dangerous radiation, with a half-life of 28 years.
Studies of the content of strontium-90 in the teeth of children born before and after nuclear tests convinced President John F. Kennedy to sign the Partial Nuclear Test Ban Treaty with the UK and Russia, putting an end to the underground testing of nuclear weapons. The Chernobyl disaster of 1986, when an explosion at a nuclear plant in Ukraine spread radioactive waste across the western USSR and a large part of Europe, polluted a large area with strontium-90.