Chemical expansion with a dilatometer
Chemical expansion refers to lattice swelling caused by vacancy formation, missing atoms, in a polycrystalline material lattice during heating. When vacancies are create the local charge changes in the lattice and causes swelling. This type of swelling/expansion is called chemical expansion and can measured in a Linseis dilatometer.
Chemical expansion, vacancy creation, occurs in all materials to some degree or another to satisfy thermodynamic laws of entropy. Vacancy creation adds disorder to the material during heating to satisfy the conditions of these thermodynamic laws.
Chemical expansion properties are useful for devolping fuel cells and ionic conductor / sensor technologies. These types of materials have specially formulated stoichiometry to create higher ionic mobility and are accompanied by higher vacancy concentration and chemical expansion.
Chemical expansion can be used to measure vacancy mobility and ionic mobility, which are related properties needed to develop these types of technologies. Chemical expansion can be detrimental in these technologies since chemical expansion can lead to internal stress in the parts.
Chemical expansion is customarily measured in a dilatometer for ceramic oxides by heating the material in different oxygen levels over constant temperatures. The CTE expansion of the material, in this way, can be separated from the chemical expansion contribution.
Push rod dilatometers can be built to include electrical leads to measure the electrical properties as the vacancy concentration changes. Investigators use the dilatometer to evaluate and compare different material stoichiometric formulations for the end application.