Ultra low and negative expansion glass-ceramic materials produced from pyrophyllite and blast furnace slag

Ultra low and negative expansion glass-ceramic materials have been obtained from pyrophyllite and blast furnace slag.. The batch composition was modified with the addition of lithium carbonate, hydrated alumina, boric acid and nucleating agent (titania). The batch was melted at 1400 degrees C followed by casting in the form of bars and annealed at 510 degrees C for 4 h. The annealed specimens were subjected to heat treatment at predetermined temperatures selected from DTA study of the parent glass. Thermal expansion measurement and X-ray diffraction analysis revealed that the specimen. nucleated at 545 degrees C for 4 h and crystallized at 720 degrees C for 2 h which resulted in negative coefficient of thermal expansion [(-) 9 to (-) 2 x 10(-7)/degrees C] over the temperature range (30-600 degrees C) due to the formation of beta-eucryptite while other heating schedule showed the formation of spodumene and lithium aluminium silicates. The samples showed excellent flexural strength value and varied in the range 120-200 MPa depending upon the phases present