Thermal Expansion of Silicon Between 293 K and 873 K Using a Capacitor Dilatometer

Abstract

A fused silica dilatometer consisted of a rod and tube that had capacitance discs attached at one end. The cylindrical specimen of polycrystalline pure silicon 2.54 cm long and 0.635 cm in diameter was clamped between the other end of the rod and tube. These were enclosed in a fused silica furnace tube within the furnace. The furnace tube was sealed with helium that did not flow. The capacitance discs were sealed in a container outside of the furnace. Helium flowed within that container. These disks were used to measure the thermal expansion of pure silicon between 20 °C and 600 °C. The capacitance measurements were made by an Andean Hagerling capacitance bridge with a readout of ten digits and a sensitivity of 0.5 attofarads. The rate of heating and cooling was 1 °C·min⁻¹. The specimen temperature was measured using a calibrated platinum thermometer 3 mm away from the specimen. To correct for changes in disc expansion during a test, a silicon diode measured the temperature. Calibration of the capacitor extensometer was made using NIST fused silica and NIST stainless steel. The total thermal expansion of three silicon specimens measured between 20 °C and 600 °C was 2074.83 µstrain with a standard deviation of 17.43 µstrain. The hysteresis difference between the warming and cooling curves for the silicon was less than 7 µstrain.