Thermal Expansion of Polycrystalline Graphite

Abstract

Thermal expansion characteristics of a group of polycrystalline graphites have been measured to 2400°C by a method which permits acquisition of meaningful expansion data without resorting to reference standards. Direct measurements on specimens while in the furnace were accomplished by using two 8-in. focal length Gaertner optical micrometers. Thermal expansion behavior is discussed in relation to orientation, impurity, degree of crystallinity, and grain size. Specimens were heated from room temperature to 2400°C, then cooled to room temperature, taking measurements of thermal expansion throughout both heating and cooling cycles. The existence of hysteresis is observed and discussed.