Dr. rer. nat. Monika Backhaus-Ricoult | Corning Incorporated | France
Many traditional refractories contain a continuous intergranular glass, which controls their electrical and mechanical properties. Typically, glass forming additives are used during ceramic processing to control the intergranular glass composition and associated ceramic properties.
A novel approach for intergranular glass engineering is presented. In most refractories, the grains are insulating, while network modifier cations in the intergranular glass are mobile at high temperature. In the novel approach, cations in the intergranular glass of a fully sintered ceramic are driven towards an external sink or from a source, thereby optimizing the glass composition and achieving desired ceramic properties.
We determined cation mobilities in intergranular glass of several model ceramics as function of alkali content and temperature, established relationships between intergranular glass composition and electric resistivity, fracture and creep properties of the ceramic and derived a clear dependency of the ceramic properties on cation level and cation mobility in the glass. We then used an electric field at high temperature to drive mobile cations between an external cation source/sink and the ceramic’s intergranular glass and successfully modified electric resistivity and/or creep over several orders of magnitude. We followed the changes in electrical properties in-situ by impedance spectroscopy during the treatment.