The creep which occurs above 600 °C is a limiting factor for their utilization at elevated temperatures. Above 750 °C their mechanical properties deteriorate due to commencing crystallization which also hampers their suitability as reinforcement in composites designated for elevated temperatures.
The composite pyrolysed at 650 °C revealed the best room — temperature properties. Its exploitation in a common environment up to 550 °C is possible but some reduction of strength and fracture toughness must be taken in consideration which takes place already after its short-time exposition in hot air.
Martin Černý, Zbyněk Sucharda, Petr Glogar;
Institute of Rock Structure and Mechanics, Academy of Sciences of the Czech Republic, Prague.