Published on 28 January 2013
Ground-breaking work by TWI's Ceramics group, on a new insulating material, looks likely to take the refractories industry by storm.
TWI has been involved in the development of thermal insulation systems for more than 12 years. Much of its effort to date has been directed at the gas turbine sector. However, this recently developed material may have a significant impact in the refractories industry.
The material, TeMuST, is a low density, highly insulating material, capable of operating at 1800oC and has outstanding resistance to liquid metal attack.
High-temperature thermal insulation is commonly used in applications such as liquid metal containment and furnace linings. Typical examples include fire-bricks and fibre products. Bricks are usually simple combinations of oxide particulates combined with a matrix and then fired. They are not as good thermal insulators as fibre products, and are heavier, but they do have the advantage of being relatively impervious to liquid metal and gases.
Fibre products are very light and have excellent insulation properties, but can suffer from shrinkage in use. There are also perceived concerns over health and safety, particularly during installation.
There has been a long-term need in the refractories industry for a material capable of operating at high temperatures, offering good insulation properties and which is impervious to liquids. TeMuS fits this specification.
It is based on bubble alumina (thin-walled, hollow spheres of alumina approximately 1.5mm in diameter) bonded together with spinel (magnesium aluminate, MgAl2O4).
Similar structures are known in the industry; but the way spinel is incorporated into TeMuS is novel. The spinel is derived using chemical precursors that react together to produce the final composition. The liquid precursors are poured into a mould containing the bubble alumina. The assembly is heated to give it acceptable green strength and then the unbaked brick is removed from the mould and fired. The precursors react to produce the spinel, and also react with the surface of the bubble alumina spheres, to produce the unique features of TeMuS.
The properties of TeMuS are impressive; including a thermal conductivity of 0.4 W/m.K, a density of 1.1Mg/m3 and virtually zero permanent linear change on heating. Full details are available from TWI.
TeMuS also shows excellent performance in terms of resistance to liquid metal attack, as demonstrated using a slag-pot test.
A 100mm cube of TeMuS had a 50mm diameter by 50mm deep plug removed, and then filled with solid aluminium. The assembly was then heated to 1300oC for three hours before cooling to room temperature. On removal the sample was sectioned. There was no evidence of chemical interaction whatsoever. The solid plug actually fell out of the TeMuS mould, as shown in the Figure.
TeMuS shows an impressive combination of thermal insulation, low density and high temperature capability and combined with its low shrinkage offers a realistic alternative to currently available firebrick and fibrous materials. Furthermore, it is anticipated that a sprayable version will be developed.
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