Itac uses Antimony

Elizabeth Henderson
Product Development Manager
ITAC Ltd

This month we stay in Group 5 of the periodic table, skipping down from phosphorus over arsenic and landing on antimony. The first known application of antimony in the coatings industry was as make-up. Antimony’s naturally occurring compound black stibnite (Sb₂S₃) was used as eyeliner by the vain in ancient Egypt, but as antimony is poisonous its use has been discontinued. ‘Tartar emetic’ (antimony potassium tartrate) was formerly used as an anti-helminthic, which acted by poisoning intestinal worms. Antimony metal exists in only one crystal form viz trigonal crystals. Antimony is found as the metal in Finland, but most of the world’s current supply is mined as stibnite in China.

Itac uses antimony by incorporating antimony trioxide, Sb₂O₃, in the fire resistant coatings we make for textiles and films.  It acts in synergy with chlorine-containing organic compounds to form free radicals in the flames, which quench combustion. In addition to this, the antimony promotes the formation of a carbon-based char on the surface of the burning material, which prevents continuing vapourisation of the fuel. Antimony oxide can also be incorporated in plastics to improve their fire performance.

Antimony played a big part in the advance of printing. In common with cast iron and water, the liquid form is denser than the solid at temperatures immediately above the freezing point. This implies that when poured into a mould it will expand into the crevices as it sets, forming a perfect cast of the void. Gutenberg exploited this property of antimony and developed an alloy of tin, lead and antimony which had the ideal hardness, smoothness and sharpness of edge for making type for printing presses. A similar material was formerly used for making typewriter keys.

Because of its nature as a semiconductor, antimony has many more modern applications than in simple pesticides and letterpress. It can be used as a Hall Effect sensor for measuring electric current and magnetic fields. It is also used to strengthen lead electrodes in vehicle batteries – pure lead is very soft and would not withstand vibration in an engine cavity without help. A major source of antimony for industrial applications is recycled vehicle batteries. An alloy of antimony with germanium and tellurium (Ge₂Sb₂Te₅) has recently been patented for use in a nanodimensional flexible screen which can display an image less than a tenth of a millimetre in diameter.

Why we use Phosphorus in our fire-resistant coatings

Elizabeth Henderson
Product Development Manager
ITAC Ltd

Phosphorus plays a dual rôle in the context of fire – it is used in matches, and at Itac we incorporate it in our fire-resistant coatings. The element was first isolated from animal urine, and this gives us a clue as to its ubiquity. Phosphorus is a key component of all living organisms, found in nucleic acids and playing a major part in cell biochemistry. The element itself is comparable to its neighbours in the periodic table, carbon and sulphur, in that it exists in more than one crystal form. White phosphorous is a tetrahedron of atoms in either a body-centred cubic (α-form) or triclinic (β-form) array. Both these forms will gradually decompose to amorphous red phosphorus with time. White phosphorus is very reactive and must be stored in water to prevent it bursting into flame

Itac’s inclusion of organic phosphate esters in fire-resistant coatings is effective because at high temperatures the organic part of the material burns away and when the residual phosphorus is further heated it will form a polymeric form of phosphoric acid. This acid causes a char layer, which shields the remaining material from oxygen, in that way preventing the formation of flammable gases.  Organic phosphate esters are liquid – this means they are readily incorporated in our mixes and compatible with the organic solvents we use.  They have the advantage of being halogen-free, so no volatile acids are formed as by-products in a fire.

 The only source of phosphorus for the modern chemical industry is phosphate rock, and large deposits of phosphate from igneous rock are found in Canada, Russia, and South Africa. ‘Coprolites’ discovered in 1842 in Suffolk were formerly mined for use in fertiliser due to their high phosphate content. They are fossilised animal dung and for some time they were a major raw material for fertilisers but their use diminished towards the end of the 19^th century.

In addition to the uses we make of phosphorus at Itac and their application in fertilisers, its compounds are very effective surfactants. Phosphate end-groups on polymer chains allow a molecule to have an affinity for both hydrocarbons and polar surfaces, allowing their use as wetting agents for materials such as pigments. Phosphorus is also an important component of phosphor bronze – an alloy of copper, tin and phosphorus which has excellent mechanical and workability properties.

Silver - more valuable than you think

Elizabeth Henderson
Product Development Manager
ITAC Ltd

Silver was formerly seen every day in our pockets – although it has been superseded in British coins it still works in many other contexts. Its ductility and malleability means it has been used since ancient times to make jewellery, ornaments and luxury items. At Itac we exploit its properties as a biocide – silver ions when in contact with bacterial DNA prevent its replication and appear to do this by interrupting the S-S bonds in the molecule. We can incorporate small amounts of silver containing compounds in coatings to exploit this effect. Silver nitrate in a block or as a solution was applied to skin infections to kill the bacteria in the nineteenth century, but in the twenty-first silver nanoparticles have been developed for use in textile medical dressings.

In other parts of the chemical industry, silver has been used as a catalyst for production of ethylene oxide and formaldehyde, particularly for ethylene oxide which is used as a building block for polyesters (step to polyurethanes). Itac uses these catalysts indirectly as we use a number of polyester PUs in our products for textiles.

The photosensitivity of silver was exploited to make pictures from early developments in the 1830s until the present day, although its use diminishes as digital photography improves. Colourless silver ions are reduced to black particles of silver metal by visible light, and will form a ‘shadow’ of a pattern placed between the silver ions and a light source. Over this time, the technology for using silver was refined from silver nitrate solution on a glass plate to emulsions of silver nitrate in gelatine on a flexible film.

Silver-containing materials also play a major role in everyday electrical items due to its excellent conductivity. Inks formulated with silver are used to produce printed circuit boards and other items such as contact films beneath computer keyboards. The heating elements on car rear windows are made of silver-based ink to conduct both electricity and heat across the glass.

Sulphur - part of Itac's cornerstone technology

Elizabeth Henderson
Product Development Manager
ITAC Ltd

Sulphur is this month’s topic.  It occurs naturally as the yellow element and is widely used in the chemical industry. Sulphuric acid consumption per capita is used as an index of industrialisation in the same way as titanium dioxide consumption.  Like carbon, discussed in Itac’s first technical blog, sulphur demonstrates the property of allotropy with dozens of stable crystal forms, but unlike carbon these different structures do not influence the way sulphur is used by us. Here at Itac sulphur is part of our cornerstone technology – rubber processing.  Organic sulphur-containing compounds such as diphenylthiourea or (straight-chain example) tetra methyl thiuram disulphide are mixed with the rubber in the milling stage, as an accelerator for elemental sulphur which is also in the mix.  As Itac’s focus is on putting rubber into solution, the mix has to be processed carefully at controlled temperatures or the hydrocarbon-sulphur bonds become too numerous and the rubber will not dissolve. This phenomenon is known as ‘scorching’. Rubber compounding does not rely solely on sulphur – the pre-milling stage incorporates pigments, fillers, oils, stearic acid and zinc compounds. As discussed in an earlier blog, zinc plays a vital role in this process. The formulation determines the final mechanical and chemical properties of the finished rubber article – for example, incorporating carbon black at this stage hardens and strengthens the finished article.

Sulphur also makes a valuable contribution in our coloured materials. We use ultramarine powder to give a blue colour to some products. Although the original ultramarine pigment was powdered lapis lazuli, modern ultramarine is made by heating powdered sulphur, sodium sulphate and sodium carbonate in the presence of iron-free clay and a reducing agent such as coal or pitch. The beautiful blue colour arises because of the S₈ groups caught in the aluminosilicate cage.

An area of adhesive technology exploiting sulphur’s chemistry is in crosslinking epoxies. Although the epoxy link will cross-link with amine, this reaction generally requires high temperature for initiation. A mercaptan group in the mix catalyses the reaction by reacting with the amine to form a mercaptide ion, which readily opens the epoxy link. The low activation energy for this process means the reaction can occur at room temperature, allowing epoxy technology to be used on heat-sensitive substrates.