Microwave assisted processing of Nanocrystalline Barium Titanate based capacitor devices

Interest towards fabrication of nanostructured electro ceramic devices has witnessed exponential growth in recent years, owing to the requirements of miniaturization, multifunctionality and improved reliability. The major hurdle in realising the full potential of nano ceramics is preventing the unwanted grain growth whilst achieving high densification during conventional high temperature processing. In this project, a detailed study was performed on the fabrication of nanostructured barium titanate based X7R multilayer ceramic capacitors (MLCCs) using microwave assisted heating. The main processing stages involved in MLCC manufacture were; (i) nano BT powder synthesis, (ii) making nano BT ink formulations suitable for screen printing, (iii) sintering of components using conventional, microwave, hybrid heating methods and (iv) performance evaluation of the end products. (Continues...)

Thermal ablation behaviour of ultra-high temperature ceramic matrix composites made by RF enhanced chemical vapour infiltration

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Effect of coating density on oxidation resistance and Cr vaporization from solid oxide fuel cell interconnects

Manganese cobalt spinel oxides are promising materials for protective coatings for solid oxide fuel cell (SOFC) interconnects. To achieve high density such coatings are often sintered in a two-step procedure, involving heat treatment first in reducing and then in oxidizing atmospheres. Sintering the coating inside the SOFC stack during heating would reduce production costs, but may result in a lower coating density. The importance of coating density is here assessed by characterization of the oxidation kinetics and Cr evaporation of Crofer 22 APU with MnCo1.7Fe0.3O4 spinel coatings of different density. The coating density is shown to have minor influence on the long-term oxidation behavior in air at 800 °C, evaluated over 5000 h. Sintering the spinel coating in air at 900 °C, equivalent to an in-situ heat treatment, leads to an 88% reduction of the Cr evaporation rate of Crofer 22 APU in air-3% H2O at 800 °C. The air sintered spinel coating is initially highly porous, however, densifies with time in interaction with the alloy. A two-step reduction and re-oxidation heat treatment results in a denser coating, which reduces Cr evaporation by 97%