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Pabba, D. P., Rao, B. V. B., Thiam, A., Kumar, M. P., Mangalaraja, R. V., Udayabhaskar, R., et al. (2023). Flexible magnetoelectric PVDF-CoFe2O4 fiber films for self-powered energy harvesters. Ceram. Int., 49(19), 31096–31105.
Abstract: Integrating the concept of magnetoelectric in the mechanical energy harvesters through the magneto-mechanoelectrical (MME) nanogenerators has been explored to realize the self-powered devices. The magnetoelectric interaction enabled the output performance of the MME nanogenerator under magnetic stimulus of the active components of the energy harvesters. In this perspective, we fabricated a flexible biomechanical and MME nanogenerator using PVDF/CoFe2O4 fibers composite films. CoFe2O4 fibers were synthesized by the electrospinning technique and the process parameters were optimized to achieve uniform and bead-free fibers. The structural and morphological properties were investigated through scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The structural and morphology revealed the fibers calcined at 800 degrees C with a heating rate of 2 degrees C/min produced bead-free continuous fibers with a fiber diameter of 210 nm with cubic spinel crystalline structure with a crystallite size of 34 nm. These highly crystalline fibers were used to fabricate PVDF/CoFe2O4 fibers composite films. The magnetoelectric behaviour of the films verified through polarization vs. electric field (P-E) loops under magnetic field. The leakage current density and mechanism of the composite films were investigated, and it was discovered that the mechanism was due to Schottky emission. Further the energy harvesting performance of the composite films were estimated where the nanogenerator achieved an output voltage of 13 V under biomechanical tapping force while the MME nanogenerator produced 3.5 V under a low frequency stray magnetic field of 6 Oe with a power density of 28 & mu;W/m2.
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Rendon, R. C., Udayabhaskar, R., Salvo, C., Sepulveda, E., Rodriguez, J. J., Camurri-Porro, C., et al. (2022). Evaluation of La0.8Sr0.2MnO3 perovskite prepared by fast solution combustion. Ceram. Int., 48(23), 35100–35107.
Abstract: La0.8Sr0.2MnO3 (LSM) perovskite as oxygen electrode material for the reversible solid oxide fuel cells (ReSOFC) was synthesized by the fast solution combustion method and assessed for subsequent calcination influence. The microstructural, morphological, compositional and optical properties of the obtained material were analyzed with X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM) coupled with an energy-dispersive X-ray spectroscopy detector (EDS) and UV-visible spectroscopy techniques. The XRD results showed the coexistence of rhombohedral R-3c and Pm-3m polymorphs for the perovskite phase, with a decreased fraction of the cubic phase as the temperature and/or time used for the calcination were increased. The HR-TEM images confirmed the existence of the R-3c and Pm-3m polymorphs for the sample subjected to calcination at 1300 degrees C, showing that the rapid combustion method did not allow the pure formation of the La0.8Sr0.2MnO3 phase for the calcination temperatures below 1400 degrees C, due to the swiftness of the combustion synthesis 500 degrees C for 5 min. The average grain size was found to be increased with the calcination time. The EDS analysis depicted a better agreement in stoichiometry with the theoretical composition. The apparent porosity was decreased with the increase in the temperature and calcination time due to the coalescence of the sintering pores. The sample obtained after the calcination at 1400 degrees C for 8 h exhibited 1.6% of porosity. The hardness was improved with the higher calcination time and temperature and reached a maximum value of 5.7 GPa that merely matched the bulk density. A similar trend was observed in the temperature dependence resistivity studies and all the samples presented a low resistivity of similar to 1.2 Omega cm in the temperature range of 600-700 degrees C. The optical characterization exhibited a broad absorption in 560-660 nm.
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Vivanco, J., Jakes, J. E., Slane, J., & Ploeg, H. L. (2014). Accounting for structural compliance in nanoindentation measurements of bioceramic bone scaffolds. Ceram. Int., 40(8), 12485–12492.
Abstract: Structural properties have been shown to be critical in the osteoconductive capacity and strength of bioactive ceramic bone scaffolds. Given the cellular foam-like structure of bone scaffolds, nanoindentation has been used as a technique to assess the mechanical properties of individual components of the scaffolds. Nevertheless, nanoindents placed on scaffolds may violate the rigid support assumption of the standard Oliver-Pharr method currently used in evaluating the Meyer hardness, H, and elastic modulus, E-s, of such structures. Thus, the objective of this research was to use the structural compliance method to assess whether or not specimen-scale flexing may occur during nanoindentation of bioceramic bone scaffolds and to remove the associated artifact on the H and E-s if it did occur. Scaffolds were fabricated using tricalcium phosphate and sintered at 950 degrees C and 1150 degrees C, and nanoindents were placed in three different (center, edge, and corner) scaffold locations. Using only the standard Oliver-Pharr analysis it was found that H and E-s were significantly affected by both sintering temperature and nanoindents location (p < 0.05). However, specimen-scale flexing occurred during nanoindentation in the 1150 degrees C corner location. After removing the effects of the flexing from the measurement using the structural compliance method, it was concluded that H and E-s were affected only by the sintering temperature (p < 0.05) irrespective of the nanoindent locations. These results show that specimen-scale flexing may occur during nanoindentation of components in porous bioceramic scaffolds or in similar structure biomaterials, and that the structural compliance method must be utilized to accurately assess H and E-s of these components. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
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