Dilatometer as a scientific tool

Abstract

Dilatometry is defined as the dimensional change of a solid specimen recorded during temperature schedule. Set of data obtained in such a manner are known as dilatogram. Dilatograms for different sort of materials represent an important trace for deduction of other materials properties than volume. Property parameters directly appointable from the dilatogram graph are: thermal expansion coefficient for the temperature interval, glass transition temperature, phasetransition temperature, sintering shrinkage and sintering temperature for maximal shrinkage rate, crystallization point temperature for amorphous bulk metallic glasses, defect annealing temperature. From dilatometric data we can also calculate more complex values such as the sintering activation energy, deduce sintering kinetic mechanisms, for the phase transition kinetic parameters and phase composition, defect concentration, materials thermal expansion coefficient at a particular temperature, solid state reaction kinetic parameters. Dilatometric devices regarding the construction are divided into contact and non contact ones, for they physically exert force on the specimen or not. Furthermore, contact dilatometric devices can be ascribed due to their construction as vertical and horizontal. This categorization leads to different and changeable contact force on the specimen. Vertical dilatometers usually use higher and temporarily changeable forces applied on the specimen. They can be, with suitable equipment, used for other mechanical properties determination than expansion, such as compressibility, tension or inflection. Non contact devices are divided into interferometric and optical. Interferometric ones use a two laser beams construction where for the length change measuring they count the number of wave lengths that are formed as a path difference between two beams. Optical devices, however, uses monochromatic light projected on the specimen that forms shadow recorded on an optical sensor. Obtained images are then analyzed for the specimen`s dimensional change.