Dilatometry

Dilatometry Method

Dilatometry is used to measure dimensional changes of a rigid solid material due to thermal expansion or contraction. In a Dilatometry experiment, a sample of specified dimensions is fixed in a holder, and a cylindrical furnace is moved to enclose the sample uniformly on all sides. The sample is subjected to a controlled rate of heating or cooling in the furnace. 

The change in linear dimensions is typically measured by mechanical, optical interferometry, thermomechanical or thermo-optical methods. In the mechanical Dilatometry technique, a push rod in contact with the end of the sample transmits linear displacement to a displacement sensor system outside the furnace. In optical interferometry, optical sensors are used and the displacement of the ends of the sample are measured in terms of the number of wavelengths of a monochromatic source. In the thermomechanical method, the change in linear dimension is transmitted to a transducer that converts mechanical displacement into a corresponding electrical signal. In thermo-optical analysis, the dilatometer is equipped with a camera, a light beam focused on the sample from one side and the shadows are recorded on the other side. 

Based on the data obtained from the above tests, a computer calculates the change in length of the sample. Various Dilatometry furnaces and sensor configurations are available and some can accommodate specimens of non-standard size. Heating upto 2500 ⁰C is possible, depending on the furnace and push rod material and design. Cooling can be done to cryogenic conditions using cold Nitrogen or Helium gas.

Dilatometry is used to test thermal expansion and contraction properties of ceramics, glasses, metals, and polymers.

Common Uses of Dilatometry

• Provide thermal expansion and contraction data for engineering design of components
• Evaluation of thermal stresses in engineered materials, components and structures
• Study Phase transition in alloys

Advantages of Dilatometry

• Quick, simple and precise technique
•  Controlled rates of heating and cooling can be applied
• Comparative dilatometry of different samples can be accomplished

 Limitations of Dilatometry

• Creep and elastic strain effects may cause error in certain materials
• Equipment and instrumentation limitations determine the heating and cooling rates that can be evaluated

 Industrial Applications of Dilatometry

• Refractories and Industrial ceramics testing
• Insulation materials testing
• Metallurgical testing and study of phase transition in alloys
• Polymer testing