Ceramic fibre

Several types of ceramic fibres are available with good thermal and chemical resistance, low thermal mass (heat storage), resistance to thermal shock and low thermal conductivity.

Products made from these have thermal conductivities comparable to asbestos products. They are also as good as asbestos products for acoustic insulation at high temperatures where vibration is a problem. Their resistance to fluctuating of flexural stresses is not as good as that of chrysotile asbestos.

Ceramic fibres are used as refractory insulation, as dry seals and fire protectors such as fumace door seals furnace linings, gaskets, engine exhaust pipes and other high temperature pipe lagging.

Ceramic fibre textiles, like. Asbestos textiles may contain alloy wire insert or glass filament inserts when metal is not acceptable for electrical uses.

Alumina-silicate fibres are used for millboard although their cost is 2 to 5 times higher than asbestos millboard. Their thermal insulation is as good but the refractory fibres have a lower thermal mass and that makes the millboard less suitable for safes that must guarantee fireproof performance for several hours. In industrial situations, where apparatus must be heated discontinuously, analogous requirements for high thermal mass favor chrysotile asbestos.

Continuous ceramic fibres are used for flexible electrical insulation and as packing in bulk and felt form, between refractory bricks.

Various type, of ceramic fibres and continuous ceramic fibres are presented hereunder:

Ceramic Fibre  Temperature limits Forms available
Aluminosilicate 1260-14000C
Aluminosilicate with chromia 15000C
Alumina and zirconia 16000C Bulk fibre, blanket, board, preformed shapes, paper
Continuous ceramic fibre  Temperature limits Forms available
Alumina-boria-silica 13000C Yarn, roving, fabric braid, chopped fibres
Alumina-chromia-silica 14000C Yarn roving, fabric, braid, chopped fibres
Zirconia-silica 16000C Yarn roving, fabric, braid, chopped fibres
Silica or Quart 1000-14000C Yam and various textile products
Mullit (72% alumia & 28% silica) 1250-15000C

Ceramic fibres range in cost from 2 to 200 US $/kg and so they cost from 3 to 100 times more than the chrysotile asbestos for which they are substitutes.

The following properties have been reported for refractory fibres:

Fibre

Temperature limits

0C

Tensile strength

MPa

Modulus

GPa

Refractory fibre 1260-1427 1700
Quart 1204 870
Alumina 1400-1700 340-410
Aluminosilicate 1760-1790 1400-2760 103-110

It should be mentioned that silicon containing refractory fibres that are kept at high temperatures (over 9000C) for a long time may recrystallize to crystobalite which is more hazardous than asbestos.

Substitutes for asbestos – Marcel Cossette