Dilatometry

What is it?

Dilatometry is the measurement of dimensional change (contraction and expansion) which a material undergoes as a function of temperature when subjected to a controlled temperature programme in a controlled atmosphere.

What is it used for?

For many materials, the dimensional changes which occur during heating and cooling can be used to determine the extent to which a material can be used, the size and shape which may be formed, its compatibility with other materials (e.g. when the aim is to join them), as well as to provide data that can be used to establish optimal processing conditions and determine the best use for the material. For example, in the ceramics industry these conditions may be the raw material formulation, the size and shape to be formed and firing cycles. This technique also allows the coefficient of thermal expansion to be calculated. The dimensional properties of a material also influence the thermal shock resistance.

The areas of application for this technique are mainly in the research and development of new materials, metallurgy and the ceramic industry.

Equipment and working conditions

The equipment used to perform dilatometric tests is a Diferentz 402 ED differential dilatometer from Netzsch.

To perform this analysis, it is necessary to take into account certain parameters such as sample size (which should be equal to the size of the reference sample), the rate of heating/cooling, surrounding atmosphere (possible also in vacuum), reference sample and thermocouple type. The dilatometer has an oven that allows temperatures of around 1500 °C to be reached.

Example of use

There are several applications of dilatometry in research and production environments to determine the coefficient of expansion or shrinking, phase transitions, sintering temperature and shrinkage steps, volume expansion, density change, softening temperatures, influence of additives on materials, optimisation of burning processes and the study of kinetics. Precise measurements of the dimension change are widely used in the ceramics and metallurgical industries.

These uses are of particular note:

• Calculation of thermal expansion of the ceramic material and its covering glaze so as to verify whether it is compatible with the ceramic mixture;
• Expansion and shrinkage behavior of technical ceramics during sintering;
• In the metallurgy industry, dilatometry enables the determination of phase changes in which dimensional variations, allotropic transformations, precipitation phenomena, Curie points and order-disorder transformations occur in alloys.