Barium is the chemical element with atomic number 56, symbol Ba.
Barium oxide was discovered in 1774 by Carl Wilhelm Scheele in manganese dioxide
ores. It was isolated in 1808 by the Englishman Sir Humphry Davy, then purified
by Guntz in 1901. The word barium was coined from the Greek ¦Â¦Á¦Ñύς ("heavy")
Barium has 40 known isotopes with a mass number between 114 and 153, and 10
nuclear isomers. Among them, six isotopes are stable, 132Ba, 134Ba, 135Ba,
136Ba, 137Ba and 138Ba. A seventh isotope, 130Ba, is theoretically unstable but
so little radioactive that less than one nucleus out of a hundred billion has
disappeared since their synthesis in supernovas (it is therefore a primordial
radioisotope with a very very long half-life). The instability of barium 130 was
discovered in 2009 by geochemical methods, by detecting the presence in rocks of
its son isotope, xenon 1308; it decays by double electronic capture (absorbing
two electrons and emitting two neutrinos), with a half-life between 0.5 and 2.7
¡Á 1021 years (about 100 billion times the age of the universe).
These seven isotopes represent all of natural barium, the most abundant being
138Ba (71.70%), followed by 137Ba (11.23%), 136Ba (7.85%), 135Ba (6.59%) and
134Ba ( 2.42%), 132Ba and 130Ba each representing 0.1%. The standard atomic mass
allocated to barium is therefore 137.327 (7) u.
Characteristics
Dendritic barium preserved under argon.
Witherite (or barium carbonate, toxic).
It is a soft, silvery alkaline earth metal that melts at 850 ¡ã C. It is found in
nature in the form of barite BaSO4, benstonite (Ba, Sr) 6 (Ca, Mg, Mn) 7 (CO3)
13, norsethite BaMg (CO3) 2, sanbornite BaSi2O5 and witherite BaCO3. Barium is
not found as a native element due to its very high reactivity with oxygen.
Its protoxide BaO is called baryta or anhydrous baryte.
Uses
It is used pure for trapping residual gases in cathode ray tubes or as an
indicator of the presence of air in thermal vacuum tube solar collectors.
Small quantities of salts of this element (acetate, carbonate, chlorate,
chloride, hydroxide, nitrate, oxide, perchlorate, peroxide, polysulphide,
sulphate or sulphide) are used in many manufacturing, in particular:
photographic paper,
high temperature resistant lubricant;
in glasses, ceramics, enamels and porcelains and their varnishes and glazes,
barium silicates are produced by adding barium compounds, examples:
BaSO4 + SiO2 ¡ú BaSiO3 + SO3 (very high temperature)
BaCO3 + SiO2 ¡ú BaSiO3 + CO2
Ba (NO3) 2 + SiO2 ¡ú BaSiO3 + N2O5
BaO + SiO2 ¡ú BaSiO3,
in glass, barium increases the absorption of X-rays and gamma rays as well as
the refractive index without greatly increasing the chromatic aberration,
At low temperatures in a glaze, barium sulphate can precipitate in the form of
large sparkling crystals or small opaque crystals. It is also used to adjust the
coefficient of expansion or viscosity by replacing other oxides;
in pyrotechnics, barium colors the flame in apple green, nitrate and perchlorate
are preferred because they provide the oxidant;
as an opacifier in radiology. In this indication, given the high toxicity in the
dissolved state, sulphate is used, insoluble even in the acid medium of the
stomach;
sulphate is also used in drilling muds for its density;
titanate (BaTiO3) is the basis for piezoelectric ceramics. Barium titanate is
used inter alia for the insulating part of certain capacitors;
it is a constituent element of non-linear crystals (barium beta borate), used in
particular to produce frequency mixtures in optics (non-linear optics);
painting ;
in the form of barium sulphate or fixed white, it is used as a filler for paints
and varnishes,
lithopone is the insoluble pigment of barium sulphate and zinc sulphide produced
by the mixture of aqueous solutions of barium sulphide and zinc sulphate,
barium and copper silicates were made in China from the Zhou west period
(1045-771 BC) to the Han period (220 AD) as pigments: Han blue (BaCuSi4O10) and
Han purple (BaCuSi2O6).
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rhenium germanium zirconium cadmium hafnium
barium lithium beryllium strontium calcium
Tantalum gadolinium samarium yttrium ytterbium
Lutetium praseodymium holmium erbium thulium dysprosium
terbium europium lanthanum cerium neodymium scandium
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