The MgAl 2 O 4 nanocrystalline powder was synthesized using naturally available egg white and inexpensive metal nitrate salts. During this process, the freshly extracted egg white was mixed with metal nitrate salt and subsequently heated at 350 • C in a pit furnace. The entire dehydration of the aqueous solution thus facilitates the low-density fluffy mass. From TGDTG results, it was observed that maximum decomposition of the precursors occurred below 600 • C. Therefore, the calcination temperature of as-synthesized powder was set at 600 • C. The MgAl 2 O 4 bulk ceramic foam was fabricated by dispersing different loading of MgAl 2 O 4 nanoparticles in the egg white, and then coating on polyurethane sponge prior to drying and sintering at a higher temperature. The ceramic suspensions exhibit a typical shear thinning behavior, and its viscosity was found to be significantly influenced by MgAl 2 O 4 powder content. An optimum loading of 40 wt% MgAl 2 O 4 nanoparticles in the egg white was found to show maximum porosity up to 90%. The obtained ceramic foam has potential applications in catalysis, absorption and sensor.
In this study, the Ho-substituted BaZrO 3 electrolyte ceramics (BaZr 1-x Ho x o 3-δ , 0.05 ≤ x ≤ 0.20) were synthesized through a low-cost flash pyrolysis process followed by conventional sintering. The effects of Ho-substitution in BaZrO 3 studied in terms of the structural phase relationship, microstructure and electrical conductivity to substantiate augmented total electrical conductivity for intermediate temperature solid oxide fuel cells (IT-SOFCs). The Rietveld refined X-ray diffraction (XRD) patterns revealed that pure phase with Pm m 3 space group symmetry of cubic crystal system as originated in all samples sintered at 1600 °C for 8 h. The Raman spectroscopic investigations also approved that Ho incorporation in BaZro 3 ceramics. Field Emission Scanning Microscopic (FESEM) study informed a mixture of fine and coarse grains in the fracture surface of Ho-substituted BaZrO 3 sintered samples. The relative density and average grain size of samples were observed to decrease as per the addition of Hosubstitution in BaZro 3 ceramics. The electrical conductivity study was accomplished by Electrical Impedance Spectroscopy (EIS) under 3% humidified O 2 atmosphere from 300 to 800 °C. Furthermore, the total electrical conductivity of BaZr 0.8 Ho 0.2 o 3-δ ceramic was found to be 5.8 × 10 −3 S-cm −1 at 600 °C under 3% humidified atmosphere, which may be a promising electrolyte for IT-SOFCs. Recently, the proton conductive oxide ceramics have fascinated worldwide attention due to widespread applications in intermediate temperature solid oxide fuel cells (IT-SOFCs), hydrogen separation and electrolysis of steam, etc. In this context, the rare-earth cerates and zirconates with the perovskite-type A(II)B(IV)O 3 crystallographic structure are the two foremost families of proton-conducting oxides for electrochemical applications 1-4. Generally, in these categories of oxide materials, oxygen vacancies are increased by replacement of tetravalent cation B(IV) by trivalent cation M(III) as given in the Eq. (1) using Kröger-Vink notation.
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