Sharif Digital Repository

Addition of spinel (MgAl2O4) to Al2O3-ZrO2 composite inhibits alumina grain growth and produces phase boundaries that leads to formation of a ceramic matrix composite with special mechanical properties such as high temperature superplastic deformation. However, the room temperature mechanical properties of Alumina-zirconia-magnesia spinel composite (AZM) such as fracture toughness were rarely investigated by researchers. In this research the AZM nanocomposite powders were synthesized via the solution combustion method. The dense AZM composite samples were fabricated through gelcasting process. Phase analysis studies were performed on both powder and sintered samples and the effects of spinel... 

Gelcasting, as a ceramic forming technique, is getting worldwide attention, in that it can be used to make high-quality, complex-shaped ceramic parts with a wide range of powders. However, a model, which can appropriately describe the shear rate dependence behavior of the slurry in casting process simulation, is limited. Therefore, this study mainly sought to investigate the best model representing the behavior of as-prepared gelcast slurry. A premix solution was prepared with monomer/cross linker of AM/MBAM with ratio of 25:1. In this procedure, ammonium polyacrylate sodium (NHPANa) was used as the dispersant and the solid load included Al2O3/20 vol% ZrO2 powder mixture. Series of slurries... 

Addition of fine zirconia particles in the alumina matrix in order to produce ZTA composite is a well-known method for improving the mechanical properties of alumina ceramics such as flexural strength and fracture toughness. Increasing homogeneity and reducing alumina grain size are two key factors for achieving proper mechanical properties in this ceramic matrix composite. In this work two batches of ZTA powder precursor were prepared through mixing of alumina and zirconia by ball milling and in situ synthesis of ZTA composite via solution combustion method. The bending strength testing samples were fabricated through gel-casting process. The effects of different powder processing methods... 

Operation of solid oxide fuel/electrolysis cells (SOFC/SOEC) at high temperatures (T > 850 °C) is accompanied by degradation phenomena, which severely affect the operational lifetime of the cell. Degradation processes are expected to occur slower at low temperatures. However, significant reduction in electrocatalytic activity of the oxygen electrode, is one of the major challenges in decreasing the operating temperature down to 500 °C-650 °C. Recently, Pr6O11 infiltrated Ce0.9Gd0.1O2 (CGO) based electrodes have been proposed to realize high electrochemical performance at intermediate temperature. In this study, Pr-oxide has been infiltrated into a well performing sub-micro... 

Insufficient electrocatalytic activity for oxygen reduction/evolution in lanthanum strontium ferrite (LSF) perovskites at temperatures below 700 °C, limits the utilization of these Co-free oxides as oxygen electrodes for intermediate-temperature solid oxide fuel/electrolysis cells (SOFC/SOEC). Marked performance improvement is here reported by decorating the surface with Pr2Ni1-xCuxO4 catalyst particles. Infiltrating porous LSF electrodes with aqueous nitrates solutions containing Pr, Ni and Cu, targeting the compositions Pr2Ni0.7Cu0.3O4 and Pr2Ni0.6Cu0.4O4, significantly reduces the polarization resistance at 650 °C from 0.98 Ω cm2 to 0.16 Ω cm2 and 0.13 Ω cm2 respectively. Electrical...