Strontium

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

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.

Stron­tium-90

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.

Sources: Paul Par­sons, Gail Dixon — The Pe­ri­od­ic Ta­ble A vis­ual guide to the el­e­ments (p.94); Wikipedia; Wikipedia