ELECTRICAL-PROPERTIES OF CARBON FIBER SHIRASU GLASS COMPOSITE/

A kind of aluminosilicate glass, shirasu glass, with a chemical compos ition (mass%) of 75.4 SiO2, 14.6 Al2O3, 0.2 TiO2, 1.7 Fe2O3, 0.2 MgO, 1.5 CaO, 3.0 Na2O and 3.6 K2O was pressureless-sintered to full densit y in air at 1000 degrees C. The dense glass showed specific resistivit y of 1440 Ohm m at 350 degrees C and activation energy of 71.7 kJ/ mol at 200-800 degrees C. These values were comparable to those for compo sitions of 25-35 mol% R2O in the R2O-SiO2 glass (R = Na, K) and associ ated with the enhanced migration of Na and K ions resulting from the s ubstitution of Al for Si in shirasu glass and the relatively large ope n glass structure. A carbon fiber (40 vol%)/shirasu glass (60 vol%) co mposite was formed by filtration of an aqueous suspension and hot-pres sed to full density at 1000 degrees C under a pressure of 10 MPa in a N-2 atmosphere. The specific resistivity of the composite was lower in parallel (0.04 Ohm m at 350 degrees C) than it was when perpendicular (14.6 Ohm m at 350 degrees C) to the direction of hot pressing. The a ctivation energy when perpendicular to the direction of hot-pressing ( 68.5 kJ/mol) was comparable to that of shirasu glass. Little temperatu re dependence of the conductivity was measured in parallel to the dire ction of hot-pressing. The above results for the composite were discus sed using the mixed conduction mechanisms of ions and electrons, which were affected by the orientation of the carbon fibers. (C) 1997 Elsev ier Science Ltd. All rights reserved.