Exchange-bias and superparamagnetic behaviour of Fe nanoparticles embedded in a porous carbon matrix

Combining different experimental techniques, the physical properties of Fe nanoparticles (NPs) randomly dispersed in a porous carbon have been investigated. From the analysis of TEM images and the broad maximum observed in ZFC–FC magnetization measurements under an applied magnetic field of 2.5 mT, a broad-size distribution NPs (5–50 nm) is estimated. The nature of these NPs (α-Fe and γ-Fe) was determined from X-ray diffraction. Furthermore, magnetization measurements suggest that these Fe-NPs remain completely blocked below 60 K due to a magnetic exchange-bias coupling induced on the surface of these NPs. However, the true nature of the core–shell responsible for this exchange bias within the NPs, is not totally understood yet. In addition, the system begins to be magnetically unblocked above 60 K, becoming almost superparamagnetic above 200 K. Room temperature Mössbauer spectroscopy confirms the existence of both α- and γ-Fe phases; an additional quadrupole component is required to properly fit the spectrum, which could be associated with the NP’s shell or to an oxide phase probably located on the surface of the NPs.     

Structural and magnetic study of mechanically alloyed Fe30Cr70 by neutron thermo-diffractometry and magnetization measurements

The temperature dependence of magnetization together with neutron powder thermo-diffraction show that nominal ball milled Fe₃₀Cr₇₀ for 110 h is formed of two mixed phases (Fe₂₀Cr₈₀ + Fe), both of them with body centered cubic crystal structure and very close values for the lattice parameter (～2.87 Å). On heating above 900 K, the system exhibits an irreversible structural transformation, giving rise to the homogenization of the material, and then recovering the well-defined starting composition Fe₃₀Cr₇₀. Subsequent heating-cooling neutron thermo-diffraction cycles do not show any additional transformation, thus explaining the overlapping M(T) curves after the first heating.     

Specific Heat Capacity and Thermal Conductivity Measurements of PLA-Based 3D-Printed Parts with Milled Carbon Fiber Reinforcement

This research focuses on the thermal characterization of 3D-printed parts obtained via fused filament fabrication (FFF) technology, which uses a poly(lactic acid) (PLA)-based filament filled with milled carbon fibers (MCF) from pyrolysis at different percentages by weight (10, 20, 30 wt%). Differential scanning calorimetry (DSC) and thermal conductivity measurements were used to evaluate the thermal characteristics, morphological features, and heat transport behavior of the printed specimens. The experimental results showed that the addition of MCF to the PLA matrix improved the conductive properties. Scanning electron microscopy (SEM) micrographs were used to obtain further information about the porosity of the systems.     

Phase separation mechanism in gelling aqueous biopolymer mixture probed by light scattering

Using time-resolved static and dynamic light scattering (DLS) we have studied the kinetics of phase separation in an aqueous gelatin/maltodextrin mixture upon fast cooling. The time evolution of the droplet radius is modelled for the monodisperse case under reaction-limited and diffusion-limited conditions and compared with the observed evolution of the mode associated with the droplet diffusion. For quenches to above the gelatin ordering temperature, nucleation and rather reaction-limited than diffusion-limited growth and late-stage coalescence of droplets with diameters up to 90 μm were concluded. Quenches to well below the gelatin ordering temperature seem to induce diffusion-limited growth or (delayed) spinodal decomposition (SD) to a phase-separated microstructure with slow late-stage coarsening. In deep quenches, a second slow SD or diffusion-limited cluster aggregation (DLCA) process becomes apparent from the evolution of the static structure factor; the process seems to be related to the maltodextrin gelation in the composite.     

ChemInform Abstract: Theoretical Study of Structural and Vibrational Properties of Al3N3, Ga3N3, and In3N3.

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