Use of the Retarded Solution-Reprecipitation Process to Attain a Higher Initial Permeability in MnZn Ferrites

We investigated the effect of various amounts of liquid phase on microstructure development during sintering and the resulting magnetic permeability of MnZn ferrite (MZF) samples. Our results revealed that the microstructure and the final magnetic permeability depend on the thickness of the liquid-phase film during sintering. The solution-reprecipitation (S-R) process, which is associated with an intensive microstructure development in MZF, starts when a continuous liquid-phase film of critical thickness δ_o, which wets the MZF grains, is formed. The solid-state sintering that takes place before the formation of the continuous liquid-phase film is essential for the final microstructure of MZF.     

A novel facile synthesis and characterization of molybdenum nanowires

We describe a straightforward technique to synthesize pure Mo nanowires (NWs) from Mo₆S_yI_z (8,2 <y + z ≤ 10) NWs as precursor templates. The structural transformations occur when Mo₆S_yI_z NWs are annealed in Ar/H₂ mixture leading to the formation of pure Mo NWs with similar structures as initial morphologies. Detailed microscopic characterizations show that large diameters (>15 nm) Mo NWs are highly porous, while small diameters (<7 nm) are made of solid nanocrystalline grains. We find NW of diameter 4 nm can carry up to 30 μA current without suffering structural degradation. Moreover, NWs can be elastically deformed over several cycles without signs of plastic deformation.     

Hydrothermal Synthesis of Ba-Hexaferrite Nanoparticles

Barium hexaferrite BaFe₁₂O₁₉ nanoparticles with a single-domain size were synthesized using a controlled hydrothermal process involving the LaMer–Dinger principle and the Ostwald ripening mechanism. Nanocrystalline particles of BaFe₁₂O₁₉ were obtained when the molar ratio of the precursor composition Ba(OH)₂·8H₂O/γ-Fe₂O₃ was 0.3 and the concentration of the suspension was about 1 wt%. The as-synthesized crystalline BaFe₁₂O₁₉ platelets approximately 50 nm in length and 5 nm in thickness exhibited a saturation magnetization of 40 Am²/kg.     

Hydrothermal Synthesis of Manganese Zinc Ferrite Powders from Oxides

Manganese zinc (MnZn) ferrite powders were prepared via the hydrothermal treatment of a homogeneous mixture of the raw oxides (i.e., Fe₂O₃, ZnO, and Mn₃O₄ or MnO) at temperatures of 220°-320°C in air or an inert atmosphere. The final results of the hydrothermal reactions between the raw oxides were fine powders with a heterogeneous phase composition. In addition to lower concentrations of the residual reactants (Fe₂O₃, Mn₃O₄), two types of spinel-structure-based reaction products-ferrite ((Mn²⁺,Zn)Fe₂O₄) and manganate ((Zn,Mn²⁺)Mn₂³⁺O₄)-were detected after the synthesis. The composition of the ferrite products, as well as the ratio of ferrite products to manganate products, were mainly functions of the oxidation state of the manganese that was present during treatment. The oxidation state of manganese during reaction was dependent on the valence of the manganese in the starting manganese oxide and on the atmosphere in the autoclave during reaction. When the hydrothermal reaction was conducted in air, almost-pure zinc ferrite was identified, whereas during reaction in an inert atmosphere, MnZn ferrite was formed. The kinetics of the hydrothermal reactions also were dependent on the oxidation state of manganese, as well as the temperature and specific surface area of the starting Fe₂O₃.     

Effect of dopants on the magnetic properties of MnZn ferrites forhigh frequency power supplies

The effect of additions on the magnetic properties of MnZn ferrites for high frequency power supplies was studied. The investigation revealed that various combinations of dopants added to the ferrite modify the grain boundary resistivity and the magnetic permeability spectra at constant microstructure. Particularly, the combined effect of Sn⁴⁺, Ti⁴⁺ and Ta⁵⁺ was found to increase the grain boundary resistivity in the ferrites studied and remarkably decrease the power loss at higher frequencies     

Imaging of intracellular spherical lamellar structures and tissue gross morphology by a focused ion beam/scanning electron microscope (FIB/SEM)

We report the use of a focused ion beam/scanning electron microscope (FIB/SEM) for simultaneous investigation of digestive gland epithelium gross morphology and ultrastructure of multilamellar intracellular structures. Digestive glands of a terrestrial isopod (Porcellio scaber, Isopoda, Crustacea) were examined by FIB/SEM and by transmission electron microscopy (TEM). The results obtained by FIB/SEM and by TEM are comparable and complementary. The FIB/SEM shows the same ultrastructural complexity of multilamellar intracellular structures as indicated by TEM. The term lamellar bodies was used for the multillamellar structures in the digestive glands of P. scaber due to their structural similarity to the lamellar bodies found in vertebrate lungs. Lamellar bodies in digestive glands of different animals vary in their abundance, and number as well as the thickness of concentric lamellae per lamellar body. FIB/SEM revealed a connection between digestive gland gross morphological features and the structure of lamellar bodies. Serial slicing and imaging of cells enables easy identification of the contact between a lamellar body and a lipid droplet. There are frequent reports of multilamellar intracellular structures in different vertebrate as well as invertebrate cells, but laminated cellular structures are still poorly known. The FIB/SEM can significantly contribute to the structural knowledge and is always recommended when a link between gross morphology and ultrastructure is investigated, especially when cells or cellular inclusions have a dynamic nature due to normal, stressed or pathological conditions.     

ζ-potential characterization of collagen and bovine serum albumin modified silica nanoparticles: a comparative study

In this study, bovine serum albumin (BSA) and collagen (COLL) were adsorbed independent of one another, onto the surface of silica nanoparticles (SNPs) at pH’s where the ζ-potential of the proteins were equal in magnitude, but opposite to the SNP surface to ascertain the differences in surface coverage and conformation in the adsorbed layer. In both systems, increasing the concentration of free protein resulted in an increase in protein surface coverage and ζ values, with ζ values approaching that of native protein at high surface coverage. However, a lower critical charge reversal concentration range was measured for COLL relative to BSA (COLL: 0–25 μg/mL, BSA: 25–90 μg/mL). Additionally, a considerable difference in ζ for adsorbed protein versus free protein was observed. These results when interpreted in terms of the theory of Ottewill and Watanabe indicate a higher Gibbs energy of association for COLL versus BSA on SNP surfaces, accompanied by perturbation in protein structure.     

Raman Study of the Interface between Hot-Pressed Silica Parts

We present a Raman spectroscopy study of silica glasses prepared by hot-pressing of gels. Our particular interest is the structure at the interfaces formed during hot-pressing of small parts to obtain large pieces, such as silica tubes for optical-fiber preforms. A specific feature of the interface that distinguishes this layer from the bulk is its fractal structure. The parameters of the fractal units, including their maximum dimensions in real space, are determined by the pre-hot-pressing mechanical processing. We attribute this structure to residual microcracks inherent in the surface layer of polished plates. There are no fractals at the interfaces sintered at temperatures higher than the glass transition temperature.     

Biodegradation Behavior of Coated As-Extruded Mg–Sr Alloy in Simulated Body Fluid

As-extruded Mg–Sr alloy, a kind of promising biodegradable biomedical material, was coated using micro-arc oxidation and also using a phosphate conversion coating. The corrosion behaviors were investigated using Hanks' solution. The corrosion of the as-extruded Mg–Sr alloy became more serious with increasing immersion time; that is, the corrosion pits became more numerous, larger and deeper. The micro-arc oxidation coating and the phosphate conversion coating were effective in improving the corrosion resistance of the as-extruded Mg–Sr alloy. The micro-arc oxidation coating was much more effective. Moreover, the as-extruded Mg–Sr alloy and the coated as-extruded Mg–Sr alloy exhibited lower corrosion rates than the as-cast Mg–Sr alloy and the corresponding coated as-cast Mg–Sr alloy, indicating that the corrosion properties of the coated samples are dependent on their substrates. The finer microstructure of the substrate of the as-extruded condition corroded much slower. The corrosion resistance of the coated Mg–Sr alloy depended on the coating itself and on the microstructure of the substrate.     

Influence of the Addition of Bi2O3 on the Grain Growth and Magnetic Permeability of MnZn Ferrites

Additions of Bi₂O₃ were used to promote grain growth and to increase magnetic permeability during sintering of MnZn ferrites. The results showed that small additions of Bi₂O₃ of <0.05 wt% remarkably increase the permeability of MnZn ferrites. On the other hand, addition of 0.05 wt% Bi₂O₃ induced the formation of a microstructure composed of giant grains with trapped pores embedded in a normal microstructure. The permeability of these samples showed a pronounced secondary maximum in permeability. At still higher Bi₂O₃ concentrations, above 0.2 wt%, the grain growth was retarded and a normal microstructure appeared; however, the magnetic permeability was strongly reduced.