Carbon fiber-reinforced cement as a thermistor

Carbon fiber (similar to 5 mm long, 0.5% by mass of cement)-reinforced sili ca fume (15% by mass of cement) cement paste was found to be an effective t hermistor. Its electrical resistivity decreased reversibly with increasing temperature (1-45 degrees C), with an activation energy of electrical condu ction (electron hopping) of 0.4 eV. This is comparable to those of semicond uctors (typical thermistor materials) and higher than that of carbon fiber polymer-matrix composites. Without carbon fibers, or with latex in place of silica fume, the activation energy was much lower and the resistivity was higher. The voltage range for a linear current-voltage characteristic was w ider in the absence of fibers. The current-voltage characteristic of carbon fiber-reinforced silica fume cement paste was linear up to 8 V at 20 degre es C. (C) 1999 Elsevier Science Ltd. All rights reserved.