Dat V. Quach

Direct measurement of grain boundary enthalpy of cubic yttria-stabilized zirconia by differential scanning calorimetry

A straight-forward set of experiments using differential scanning calorimetry was used to obtain the average grain boundary enthalpy at high temperatures for 10 mol. % yttria-stabilized zirconia (10YSZ) by exploiting the heat of grain growth on nanograined dense samples consolidated by spark plasma sintering. The heat of grain growth was measured and correlated with the quantified microstructure evolution during the process. The average grain boundary enthalpy of 10YSZ was found to be 1.00 ± 0.29 J m−2 for the temperature range 900–1300 °C. Comparing this result with room temperature data in the literature, small temperature dependence of the grain boundary enthalpy could be found outside the experimental uncertainties in both experiments.

Grain Size Effect in the Electrical Properties of Nanostructured Functional Oxides through Pressure Modification of the Spark Plasma Sintering Method

Through the use of a high-pressure modification of the spark plasma sintering method, it was possible to consolidate functional oxides (yttria- stabilized zirconia and doped ceria) to high densities and retain a grain size of < 20 nm. The role of the pressure on densification and on the grain size of the sintered samples was demonstrated. The pressure had a marked effect on density at relatively low temperature but an insignificant effect at relatively high temperature. It was found that when prepared with such small grain sizes, these oxides conduct protonically even at temperatures as low as room temperature. The dependence of the protonic conductivity is stronger dependence on grain size than what can be anticipated from a geometric consideration based on an increase in grain boundary area. This observation strongly suggests that factors other than an increase in grain boundary area play a role, a consideration that is being further investigated.