This study investigates the thermal expansion behavior of SrFe1-xTixO3-δ (SFT) cobalt-free cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). SFT cathodes with varying titanium dopant concentrations (x = 0.1-0.5) were synthesized via the glycine-nitrate combustion method. Increasing x effectively reduced the SFT cathode thermal expansion coefficient (TEC), approaching that of the SDC electrolyte. While lower TEC is generally favored, it was observed that increasing x correlated with increased area-specific resistance (ASR) from previous work, suggesting that factors beyond TEC mismatch influence electrochemical performance. Notably, the SF9T1 composition (x = 0.1), despite exhibiting the highest TEC among the SFT series, demonstrated the best electrochemical performance and good adhesion to the electrolyte, highlighting its potential as promising IT-SOFC cathode material. The observed TEC differences compared to prior reports emphasize the influence of the synthesis method. This work provides valuable insights into the complex relationship between dopant concentration, TEC, ASR, and interfacial compatibility in SFT cathodes for IT-SOFC applications.
Modulation calorimetry is the process of oscillating the heat input to a sample and measuring the oscillating temperature response. The process enables the determination of heat capacity and thermal conductivity. The heat capacity can be isolated using low frequency modulations since the primary mode of heat transfer is between the sample and its environment. The thermal conductivity can be calculated using higher frequencies when the transient internal conduction is prominent. When applied to electromagnetic levitation (EML), a containerless processing technique using an electromagnetic field to position and heat the sample, the thermophysical properties can be determined at higher temperatures. To optimize the procedure, a key free variable, oscillation frequency, is investigated. A correction function found in literature dictates the important heat transfer mode in the system as a function of modulation frequency. The ideal frequency for modulation to determine heat capacity can be calculated from a sample’s material properties and temperature. This is shown in terms of the Biot number, a measure for whether the sample can be assumed isothermal. For determination of thermal conductivity, the current standard is not a high enough frequency to reveal thermal gradients. Further research is needed to determine the frequency requirements necessary for measuring thermal conductivity.
Surface tension is measured for the binary alloys Al-Ti and Al-V using the electromagnetic levitation technique. The surface tension is evaluated as a function of temperature and composition. The well-established Butler model is used for discussion. The latter has recently been renovated by Kaptay but a comparison with experimental data is still lacking. It is found that the renovated Butler model yields much better agreement with the data than the conventional model does.
