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Elizabeth Henderson
Product Development Manager ITAC Ltd |
Snow-white barium sulphate is the barium compound which
brings this element to the world of adhesives and surface coatings. The
material is sometimes referred to as ‘Blanc
fixe’, or ‘permanent white’. Barium
itself is next door but one to calcium, which was the subject of the Itac blog
at the beginning of 2014, and its chemistry is similar. The principal natural
source of barium is barium sulphate which is mined in China, India and Morocco.
Barium sulphate occurs naturally in orthorhombic crystals with the structure 2m2m2m
and its pure whiteness and high specific gravity (4.5) are the properties which
we exploit in our formulations at Itac – we use it to whiten our coatings, and
the low volume it occupies in the finished film means we can incorporate a high
percentage by weight. This high
proportion can be adjusted to control the rheology of the materials we supply. Inclusion
of barium sulphate affects the appearance of the finished film, and its physical
properties such as sandability and hardness. We have also used barium sulphate
to enhance the adhesive properties of adhesives for carpets based on natural
starch.
The volume of barium sulphate used for coatings is
considerable, but most of the world’s production is used in the manufacture of
drilling fluids. These materials also exploit the high density of barium
sulphate, and its insolubility in water. The drilling fluids are slurries which
transmit the drill pressure precisely into a cavity as it forms, as well as
keeping the drill bit cool. A further exploitation of barium sulphate’s
insolubility in water is its use as a contrast agent for clinical X-rays.
Although barium salts are poisonous, they cannot be absorbed from an aqueous
suspension. The strong scattering from barium sulphate in someone’s guts allows
any structural problems to show clearly.
As well as being used
in our functional coatings barium sulphate plays a vital rôle in colour
management – it is used to whiten the inside of the sample chamber of some
colour measurement machines, ensuring that the source light falling on the
sample is as white as possible and thus the measurements as accurate as
possible.
Barium makes its contribution to æsthetics in the world of
colour – the brilliant green in last month’s fireworks came from barium in the
formulations. It is also a vital element in two of the pigments used on the
Chinese terracotta soldiers, which were painted with BaCuSi4O10
(Han blue) and the less stable but more beautiful BaCuSi2O6 Han
purple. A rare fluorescent blue gemstone is found in California and is its
official state gem – benitoite is barium titanium silicate.
