This is a repository copy of Influence of processing conditions on the ionic conductivity of holmium zirconate (Ho2Zr2O7).
The pyrochlore oxides are of potential interest as ion conducting electrolyte for intermediate temperature solid oxide fuel cell (SOFC). Nanopowders of holmium zirconate have been synthesised through ion-exchange between sodium alginate gel and metal complex solution followed by its thermal decomposition. Nanoparticles of Ho2Zr2O7 were obtained by calcining the dried gel beads at 700˚C for 2h and 6h duration respectively. An insight into calcination has been obtained employing simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA/DSC). Thermal decomposition was also followed using High Temperature X-ray Diffraction (HTXRD) in static ambient atmosphere. Results from TGA/DSC and HTXRD corroborate each other. Fine crystalline nanopowders of single phase Ho2Zr2O7 could be obtained after thermal decomposition at relatively low temperature (600-700˚C). Powder X-ray diffraction (XRD) revealed that the material has crystallized as single phase cubic Ho2Zr2O7 with defect fluorite structure. XRD and Raman spectroscopy were used to analyse the local structure of holmium zirconate. XRD scans of holmium zirconate and holmium hafnate prepared through identical method have been compared and effect of cationic radius of Zr 4+ and Hf 4+ on B-site was studied. The crystallographic data obtained from XRD and transmission electron microscopy (TEM) are in good agreement with each other. This sol gel method referred also as Leeds Alginate Process (LAP) is simple, cost effective, energy efficient and carbon neutral for the preparation of pyrochlore oxides (A2B2O7) solid electrolyte material for SOFC.
Recent advancements in thermo-fluid technology assisted with highly thermal conductive nanomaterials have shown assuring outcomes. It is also proven that thermal conductivity alone cannot define the overall heat transfer characteristics, and the viscous properties are equally significant towards thermal management. Therefore, this research involves investigating the rheological behavior of hybrid nanosuspensions containing high thermally conductive diamond and graphene nanoplatelets (1:1). These nanomaterials are dispersed in mineral oil using a two-step technique. Hybrid nanofluids' stability is achieved using a non-ionic stabilizer Span85, exhibiting no sedimentation for a minimum of five months. Nanomaterial characterizations are performed to study morphology, purity, and chemical analysis. The flow behavior of hybrid nanosuspensions is investigated at varying nanomaterial mass concentrations (0-2 %), temperatures (298.15-338.15 K), and shear rates (1-2000 s -1 ). Hybrid nanofluids exhibit shear-thinning behavior, which is also correlated with the Ostwald-de-Waele model. The temperature-viscosity relationship is well predicted using the Vogel-Fulcher-Tammann model. Hybrid nanofluids show a maximum enhancement of 35% viscosity at 2% concentration. A generalized twovariable correlation is used to express viscosity as a function of temperature and nanofluid concentration with an excellent agreement. Three different machine learning methods, i.e., Artificial Neural Network (ANN), Gradient Boosting Machine (GBM), and Random Forest (RF) algorithms are also introduced to predict the viscosity of hybrid nanofluids based on the three input parameters (temperature, concentration, and shear rate). The parity plots conclude that all algorithms can predict big-data viscous behavior with high precision.
A 2 B 2 O 7 oxides with defect-fluorite structure are one of the potential candidates for solid oxide fuel cell electrolyte material due to their excessive thermodynamic stability in oxygen potential gradient at elevated temperature between 500 and 900 °C. Holmium hafnate nanoparticles have been synthesised through the Leeds Alginate Process (LAP) using inorganic salts of holmium and hafnium as starting materials immobilized in alginate beads. Ion exchange with sodium alginate and its subsequent thermal treatment have been used to prepare the nanopowder of Ho 2 Hf 2 O 7 . Thermal decomposition of dried beads is carried out at 700 °C for 2 h and 6 h to obtain the nanoparticles of Ho 2 Hf 2 O 7 . This calcination temperature was determined after carrying out simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA/ DSC). High Temperature X-ray Diffraction (HT-XRD) was carried out to gain further insight into the thermal decomposition process in static ambient environment. HT-XRD analysis corroborated with the results obtained from TGA/DSC. Nanocrystalline powder of single phase Ho 2 Hf 2 O 7 has been obtained by calcination of oven dried ion-exchanged alginate beads in relatively low temperature range of 500-700 °C. Rietveld refinement of X-ray diffraction (XRD) data confirmed the formation of single phase defect fluorite structure of Ho 2 Hf 2 O 7 . The crystallographic parameters calculated from TEM and XRD analysis are in excellent agreement with each other. Furthermore, TEM-EDX analysis confirms that the Ho 2 Hf 2 O 7 synthesised by the facile alginate process is nearly stoichiometric. Raman spectroscopy gives evidence of the presence of oxide-ion vacancy in holmium hafnate which is supported with ac-impedance spectroscopy measurement at selected three temperatures. The present study suggests that the LAP has the capability of yielding on a large scale single phase defect-fluorite nanoparticles of electrolyte materials for solid oxide fuel cells in environmentally sustainable, economical and energy efficiently manner.
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