Date of Award

Fall 1990

Degree Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Physics

Abstract

The linear thermal expansion perpendicular to the cleavage layers of different micas has been determined using a thermomechanical analyzer. Very large and anomalous expansion similar to that reported earlier by Hidnert et al (1) has been observed in some natural phlogopite specimens, over 100% at 300°C in some cases. Cyclic measurements of thermal expansion show that the anomalous expansion is reversible with a hysteresis, particularly after the first heating-cooling cycle. The anomalous expansion is attributed to a small quantity of occluded water within the mica structure, which can accumulate on lenticular flaws and which converts to vapor at temperatures above 100°C. Increasing the stress on the phlogopite specimens, by applying various loads to the probe of the thermomechanical analyzer, displaces , the onset temperature of anomalous expansion. This effect is related to the change of the boiling point of water with pressure and an agreement is obtained with thermodynamic data. The thermal expansion at higher temperatures can be explained by the volume change of water vapor with temperature, behaving like an ideal gas. The estimated quantity of occluded water to account for the expansion behavior is very small, less than 0.02% by weight. The behavior of different phlogopite specimens can be different, depending on the quantity of water present. Such a material could be used as the basis of a thermal actuating device.

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