Dilatometry (DIL) is a technique in which a dimensional change of a substance under negligible load is measured (e.g. expansion measurement or shrinkage measurement) as a function of temperature while the substance is subjected to a controlled temperature program in a specified atmosphere.
The coefficient of linear expansion is taken as the property for the change in length. the sample is placed on a sample holder in the furnace. A push rod made of the same material as the sample holder (quartz glass, aluminium oxide) transfers the thermal expansion of the sample to a displacement transducer which measures the displacement. The displacement is measured analog or digital.
The displacement transducer is firmly attached to the reference. Since the reference and the push rod are also extended in the same way during heating, the sample expansion is measured relative to the material of the reference. The actual thermal extension of the sample is then equal to the value measured by the displacement transducer plus the expansion of a piece of reference material of the same length as the sample.
In order to record and analyze the shrinkage process qualitatively and quantitatively, the optical dilatometry method is used. The sample is irradiated with light from one side and the shadows are recorded by a camera. Based on the data obtained, a computer calculates the change in length and area of the sample.