This study investigates the synthesis–structure relationships governing sol–gel-derived nanostructured MgFe2O4 ferrite powders for high-temperature thermochemical energy conversion applications. The effects of key processing parameters, including propylene oxide (PO) concentration, gel aging time, calcination temperature, and calcination duration, were systematically examined to tune the phase composition, specific surface area (SSA), pore volume, crystallite size, and nanoparticle morphology of MgFe2O4. Increasing the PO concentration from 5 to 20 mL shortened the gelation time from 585 to 323 s and increased the SSA from 5.30 to 17.88 m2/g, while the pore volume increased from 0.0074 to 0.0210 cm3/g. In contrast, gel aging time between 24 and 120 h produced negligible changes in SSA, pore volume, and crystallite size, indicating that extended aging is not required for microstructural control. Calcination temperature strongly influenced the nanostructure: increasing the temperature from 600 to 1000 °C decreased SSA and pore volume while increasing crystallite size from 21.33 to 48.76 nm. Longer calcination times produced a similar but less pronounced effect, decreasing SSA from 18.83 to 14.89 m2/g and increasing crystallite size from 17.55 to 30.12 nm. Overall, phase-pure MgFe2O4 with favorable textural properties was obtained using 20 mL of PO, 24 h of aging, and calcination in the 700–800 °C range. Under the identified synthesis conditions, namely 20 mL of PO, 24 h of aging, and calcination in the range of 700–800 °C for 2 h, phase-pure MgFe2O4 nanoparticles with particle sizes of approximately 10–50 nm were obtained. These results establish a processing–microstructure framework for engineering MgFe2O4 nanomaterials with tunable textural properties for solar thermochemical redox cycles and related high-temperature energy applications.
Glass–ceramic nanocomposites of xV₂O₅–(40−x)Cu₂O–60P₂O₅ (x = 10–40 mol%) were prepared by melt quenching followed by heat treatment at 873 K. XRD analysis confirmed the formation of Cu₂O and V₂O₅ nanocrystalline phases with crystallite sizes in the range of 16–27 nm embedded within a partially amorphous matrix. DC electrical conductivity increased by nearly four orders of magnitude with increasing V₂O₅ concentration, accompanied by a systematic decrease in activation energy, indicating enhanced thermally activated small-polaron hopping conduction. Positron annihilation lifetime (PAL) spectroscopy revealed a gradual reduction in vacancy-type defect size and free-volume parameters with increasing V₂O₅ content, suggesting improved local structural ordering and reduced carrier localization. In contrast, the oxygen molar volume increased slightly with composition, reflecting macroscopic structural rearrangement and modification of the phosphate network. These observations indicate that the macroscopic network expansion and microscopic reduction of localized free-volume cavities occur simultaneously at different structural scales. The enhancement in electrical conductivity is primarily governed by increased vanadium ion concentration and reduced hopping distance, while defect reduction contributes indirectly through improved structural compactness and orbital overlap between neighboring vanadium ions. The present results provide insight into the correlation between structural evolution, free-volume defects, and electrical transport in transition-metal oxide glass–ceramic nanocomposites.
D. E. El Refaay, M. El‐Desoky, A. E. Harby et al.· Scientific Reports· 0 citations
NaNO3 shape-stabilized composite phase change materials (PCMs) supported by CO2‑mineralized basic oxygen furnace (BOF) slag were developed for photothermal heat storage. The effects of slag mineralization degree and NaNO3 loading on structure, phase transition behavior, thermal stability, thermal conductivity, and cycling stability were systematically investigated. CO2 mineralization converted active Ca/Mg-bearing phases in BOF slag into carbonate phases, increasing the weight gain from 9.37 to 17.45% as mineralization time increased from 30 to 120 min. Among the mineralized samples, CSS-60 provided the most favorable balance between mineralization degree and accessible porosity. Using CSS-60 as the supporting skeleton, the composite PCMs showed good shape stability. The melting enthalpies of OPT-N40, OPT-N50, and OPT-N60 were 67.43, 83.22, and 97.38 J g-1, respectively. Compared with pure NaNO3, the composites exhibited improved thermal stability and higher thermal conductivity. After 300 thermal cycles, all samples maintained good thermal cycling stability, with shifts in onset and peak temperatures below 0.5 °C and enthalpy decay below 5%. OPT-N50 showed the best overall performance. These results indicate that CO2-mineralized BOF slag is a promising low-cost and low-carbon supporting matrix for NaNO3-based medium-temperature photothermal heat storage.
Yingchun Zhao, Lili Zhang, Jianbo Ma et al.· Journal of the Brazilian Che...· 0 citations
This study investigates the interplay between dispersion, nucleation, and crystallization kinetics in HDPE/graphene nanoplatelet (GNP) nanocomposites processed under solid‐state thermokinetic conditions (10–240 min, 0.1 and 1 wt% GNP). This processing route imposes much higher shear rates and submelting temperatures than conventional melt blending. SEM analysis revealed progressive GNP fragmentation, from ~2.4to ~0.5–0.8 μm with increasing processing time. Rheological results showed a transition from reinforcement to lubrication behavior, with viscosity increasing at short times and later decreasing. DSC results indicated enhanced heterogeneous nucleation, with the onset crystallization temperature increasing by ~5°C and supercooling decreasing from ~10°C for HDPE to ~4°C–6°C for the nanocomposites. At longer times, a high‐temperature shoulder (~120°C) emerged, indicating a secondary nucleation pathway. The SbC–Sbirrazzuoli model provided excellent fitting (
F
exp
= 1.00 <
F
crit
= 1.96), but the Avrami and Nakamura models failed to capture the multistep kinetics, highlighting the inadequacy of single‐mechanism assumptions for nanocomposite systems. Activation energy analysis showed a transition from nucleation‐controlled (−620 to −500 kJ mol
−1
) to diffusion‐controlled crystallization (−300 to −450 kJ mol
−1
). Graphene induces multistep crystallization through the interplay between heterogeneous nucleation and restricted chain mobility. The proposed kinetic–mechanistic framework establishes relationships between processing conditions, crystallization kinetics, and microstructure, providing a physically based interpretation of the crystallization behavior of HDPE/GNP nanocomposites.
Lucas J. S. Nascimento, Tainá dos S. Guatimosim, F. Dias et al.· Polymer Engineering & Sc...· 0 citations
Hybrid perovskites are emerging as promising candidates for thermal management and thermal energy storage (TES). Compared to traditional solid–liquid phase change materials, these hybrids offer tunable structures, enhanced thermal conductivity, and comparable latent heats. This study extends a rapid, scalable microwave (MW)-assisted synthesis to a broader suite of organic–inorganic hybrid perovskites with the general formula (C12H25NH3)2MCl4 (where M = Zn, Cu, Mn). Beyond broadening the synthetic scope, we provide a comprehensive comparative analysis of how metal center substitutions influence material properties. The structural integrity, morphology, and phase purity were systematically characterized via XRD, SEM, EDX, and FTIR, while thermal behaviors were evaluated using DSC and TGA. The results demonstrate that the specific metal ion significantly dictates both the crystalline structure and phase transition thermodynamics. Transition enthalpies ranged from 58 to 112 J/g, with peak temperatures between 46 and 74 °C. Thermal stability also varied across the series, with decomposition onset occurring between 270 and 335 °C. By elucidating how metal selection steers performance, this work establishes MW-assisted synthesis as a versatile, energy-efficient platform for the tailored fabrication of advanced solid–solid phase change materials for practical energy storage applications.
Ali Mirahmad, Ravi Shankar Kumar, Breogán Pato-Doldán et al.· ACS Omega· 0 citations