Gadolinium-oxide nanoparticles for cryogenic magnetocaloric applications.

The series of advanced nanocomposites consisting of Gd2O3 nanoparticles (NPs) embedded into periodic porous SiO2 matrix have been investigated with respect to their structural and magnetocaloric properties. By means of small angle neutron scattering and transmission electron microscopy, regular nanopores organized in the cubic or hexagonal superlattice have been documented. The pores are occupied by the NPs of progressive concentration within the nanocomposite series. All of the examined systems have exhibited extraordinarily high values of magnetic entropy change (up to 70 J kg-1 K-1) at low temperatures with the absence of thermal hysteresis, indicating their perspective utilization in cryogenic refrigeration. Profound analysis of magnetic entropy change data via scaling laws has been applied to the nanocomposite materials for the very first time. With the aid of scaling analysis, conclusions on magnetic properties and phase transition type have been made, even for the conditions unavailable in the laboratory.

Effect of heat treatment on the morphology of carbon fibers doped with Co2p nanoparticles.

ABSTRACT: Carbon fibers (CFs) decorated by Co2P nanoparticles and carbon nanotubes were prepared via needle-less electrospinning technique. Formation of catalytically active Co2P nanoparticles and growth of carbon nanotubes were monitored in open and closed sintering environment at different sintering exposure times. Higher porosity, important in the catalytic reaction for easier penetration of electrolyte into the CFs, was achieved by mixing two immiscible polymers with natrium dodecyl sulfate and subsequent heat treatment process. Structure and morphology of the prepared modified carbon fibers were characterized by XRD, SEM and TEM. The time of heat exposure at the sintering temperature of 1200 °C and closure of the sintering space showed distinct effect on the growth and shape of carbon nanotubes. SEM and Raman spectroscopy revealed that closure of the system led to the formation of carbon nanotubes with smaller diameters and less structural disorder. Comparing of as-prepared CFs revealed that CFs with Co2P sintered in the closed system exhibited the best electrocatalytic activity for hydrogen evolution reaction due to lower overpotential and smaller Tafel slope in acidic solution.

Physical, mechanical and in vitro evaluation of a novel cement based on akermantite and dicalcium phosphate dihydrate phase.

Magnesium containing calcium silicates have recently shown that they are promising materials for various biomedical application with potential use in the form of bulk ceramic, composite scaffold or coatings on metallic substrates. A novel akermanite (AK; Ca2MgSi2O7)/dicalcium phosphate dihydrate (DCPD, CaHPO4. H2O) cement mixture was tested in this work in order to produce an alternative AK/DCPD biocement for orthopedic applications. For comparison, we have prepared two cements mixed with 2.5 wt% NaH2PO4 solution (labeled as NaH2PO4 cement) and with the solution composed of organic 2.5 wt% citric acid a 2.5 wt% trisodium citrate (citrate cement) respectively. The results demonstrated only a partial dissolution of AK, regardless of the type of liquid used. On the other hand, the DCPD was completely hydrolyzed much faster in the citrate cement. The final hydration product was an amorhous quarternary phase of CaO-MgO-SiO2-P2O5 composition with the remaining unreacted akermanite embeded in the cement matrix. The highest early compressive strength was observed in the citrate cement (33 MPa), but much lower value was measured in NaH2PO4 cement (7 MPa) after 1 d setting. Different cell responses have been observed when the cells were cultured on the surfaces of cement substrates. While the NaH2PO4 cement demonstrated high proliferation activity of osteoblast, the citrate cement showed strong cytotoxic cell response, probably as a result of higher concentration of citrates on the cement surface, which can negatively affect the attachment and proliferation of osteoblastic cells.

Fe2O3 and Gd2O3 nanoparticles loaded in mesoporous silica: insights into influence of NPs concentration and silica dimensionality.

Fine Fe2O3 and Gd2O3 magnetic nanoparticles (NPs) with sizes 7 nm and 10 nm embedded into mesoporous silica have been prepared using a wet-impregnation method. A comparative study of the reactant concentration along with the hosting matrix symmetry on mesostructuring and the magnetic properties of the nanocomposites have been investigated. Reactants with four different concentrations of Fe3+ and Gd3+ ions and silica matrices with two different kinds of symmetry (hexagonal and cubic) have been utilized for the study. The structural characterization of the samples has been carried out by the N2 adsorption/desorption method, high-energy X-ray diffraction (HE-XRD), TG/DTA, and high resolution transmission electron microscopy (HRTEM). The magnetic properties of the nanocomposites have been examined by means of SQUID magnetometry. It has been found that a range of different magnetic states (diamagnetic, paramagnetic, ferromagnetic, superparamagnetic) can be induced by the feasible tailoring of the particle concentration, the porous matrix symmetry and the composition. Furthermore, the existence of a "critical concentration limit" for embedding the particles within the body of the matrix has been confirmed. Exceeding the limit results in the expulsion of nanoparticles on the outer surface of the mesoporous matrix. Revelation of the relationships between particle concentration, matrix symmetry and magnetic properties of the particular composite reported in this study may facilitate the design and construction of advanced intelligent nanodevices.