Dilatometer

A dilatometer is an instrument used to measure dimensional changes of a material as a function of temperature, time, or stress. Most dilatometers provide a measurement of length change along a defined axis; some configurations can infer volume change from multi-axis measurements or use optical methods to detect changes.

Principle: A specimen is placed in a furnace or environmental chamber with controlled atmosphere. A displacement sensor records length changes as temperature varies. Methods include contact-based (push-rod or contact dilatometry) and non-contact optical techniques (interferometric, laser triangulation, or capacitance-based) to detect tiny elongations with high sensitivity. The data yield the coefficient of thermal expansion alpha = (1/L) dL/dT and can reveal phase transitions, sintering, creep, or dehydration through abrupt changes or changes in slope.

Types: linear dilatometers (standard), high-temperature dilatometers designed for metals and ceramics, and laser or optical dilatometers for non-contact measurements. Some systems are coupled with differential scanning calorimetry or thermomechanical analysis for multi-parameter characterization.

Applications: used in industrial materials testing (steel, aluminum, ceramics, cement), polymers, composites, and geoscience samples (minerals, rocks). They support investigation of phase transitions, sintering kinetics, thermal aging, and other temperature-dependent dimensional changes.

Advantages and limitations: dilatometers offer direct measurement of dimensional change with good sensitivity and relatively straightforward operation. Limitations include sensitivity to furnace drift and temperature gradients, sample geometry effects, and measurement lag, requiring careful calibration and data interpretation.