Application of the interferometer to measurements of the thermal dilation of ceramic materials

An interference method and apparatus for measuring the thermal expansion of ceramic materials are described. The samples in the form of tripods or small pins, 0.5 to 10.0 mm in length, are placed between two fused quartz interferometer plates and heated in an electric furnace. The elongation of the sample is determined from the number of interference fringes that pass reference marks on the upper interferometer plate. Measurements made on the thermal expansion of several samples of glaze, terra cotta, tile, porcelain, and clay show that this method gives accurate and reproducible results. These, represented by curves, show that the expansivities of different ceramic materials may differ greatly ; that the expansion of a given material may be different at different parts of the temperature scale; and that some materials may undergo permanent dimensional changes when sub- jected to heat treatment. They also serve to explain why some materials fail and others do not when subjected to the same treatment and emphasize the need of accurate data on expansivity of each material if it is to be subjected to sudden temperature changes when combined with another material differing in composition.