Friday, 5 December 2014

Barium enhances the properties of adhesives

Elizabeth Henderson
Product Development Manager

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.