Dilatometry

Dilatometry is a thermoanalytical technique used to measure the expansion or shrinkage of solids, powders, pastes and liquids under negligible load when subjected to a controlled temperature/time program.

A precise understanding of this behavior can provide insight into firing processes, the influence of additives and raw materials, densification and sintering properties, reaction kinetics, phase transitions, and thermal shock. In addition, it can be used for glaze development and to match CTEs (glaze-ceramic, metal-ceramic in the automotive industry).

Dilatometry can be applied not only to solid samples, but also to powders, pastes, and even liquids. It can also be used to carry out rate-controlled sintering studies on reactive powders in fields such as advanced ceramics or powder metallurgy.

Due to large technological advances, this thermal analysis method can now measure even the slightest of thermal behaviors in ceramics.

Method

Method

Pushrod dilatometry is a method for determining dimensional changes versus temperature or time while the sample undergoes a controlled temperature program. The degree of expansion divided by the change in temperature is called the material’s coefficient of expansion (α) and generally varies with temperature.

Principle of Operation

To perform a dilatometric analysis, a sample is inserted into a special holder within a movable furnace. A pushrod is positioned directly against the sample and transmits the length change to a linear variable displacement transducer (LVDT).

As the sample length changes during the temperature program, the LVDT core is moved, and an output signal proportional to the displacement is recorded. The temperature program is controlled using a thermocouple located either next to the heating element of the furnace or next to the sample.

Since the sample holder and the frontpart of the pushrod are being exposed to the same temperature program as the sample, they are also expanding. The resulting dilatometer signal is therefore the sum of the length changes of sample, sample holder, and pushrod.

It is thus necessary to correct the raw dilatometer data in order to obtain a true view of sample behavior. There are two correction methods: the application of tabulated expansion data, or – oftenmore precise – of a correction curve to eliminate systematic error.

DIL Measurement Information

DIL Measurement Information

  • Linear thermal expansion
  • Coefficient of thermal expansion (CTE)
  • Volumetric expansion
  • Shrinkage steps
  • Glass transition temperature
  • Phase transitions
  • Sintering temperature/sintering step
  • Density change
  • Softening points
  • Influence of additives/raw materials
  • Decomposition temperature – e.g., of organic binders
  • Anisotropic behavior
  • Optimizing of the firing process
  • Rate-controlled sintering (RCS)
  • Caloric effects by using c-DTA®
  • Thermokinetics