Structural, Electrical, Dielectric, and Magnetic Properties of Cd2+ Substituted Nickel Ferrite Nanoparticles

In the present investigation structural, electric, magnetic, and frequency dependent dielectric properties of Ni1-xCdxFe2O4 ferrite nanoparticles (NPs) (where x=0.2, 0.4, 0.6, and 0.8) prepared by sol-gel autocombustion method were studied. The crystallite size (t) (46.89~58.40 nm) was estimated from X-ray diffraction data with the postconfirmation of single phase spinel structure. Spherical shaped, fused grain nature with intergranular diffusion in Ni1-xCdxFe2O4 NPs was observed in scanning electron micrographs. The value of loss tangent (tan⁡δ) decreases exponentially with an increasing frequency indicating normal Maxwell-Wagner type dielectric dispersion due to interfacial polarization. Decreasing values of Curie temperature (TC) from 860°C to 566°C with increasing Cd2+ content x in Ni1-xCdxFe2O4 NPs were determined from AC-Susceptibility. Activation energy ΔE ranges within 0.03~0.15 eV. Decreasing magnetic saturation Ms, coercivity Hc, and magneton number nB values show the effect on nonmagnetic Cd2+ ions over magnetic Ni2+ and Fe ions.

Initial stages of oxidation of Ti45Al7Nb0.4Y alloy at 900 °C in air

The initial stage of oxidation of Ti45Al7Nb0.4Y alloy (at.%) oxidized at 900 °C in air was investigated by using x-ray photoelectron spectroscopy and Auger electron spectroscopy. Experimental results revealed that YAl2 segregated along the grain boundaries preferentially oxidized to Y2O3 and Al2O3 due to strong affinity of Y to oxygen. Oxides grew faster at the grain boundaries than in lamellar colonies. As a result, Y and Al oxides pegs protruded into the substrate, which can increase the contact areas of oxide scale and substrate. Moreover, inward diffusion of oxygen more easily occurred along the grain boundaries. As a result, it promoted the external oxidation of Al within the grains due to lower inward diffusion flux of oxygen. And coarse-grained Y2O3 blocked the cationic intergranular diffusion. Therefore, Y addition can effectively enhance the Al2O3 layer and suppress the TiO2 outermost layer.

Defects and Diffusion in d-AlNiCo-Quasicrystals - Application of Mechanical Spectroscopy

Mechanical loss (internal friction) measurements were applied to polycrystalline d- AlNiCo quasicrystals for compositions ranging from Al72.8Ni7.5Co19.7 to Al71.1Ni18Co10.9 and to an Al71.3Ni13.4Co15.3 mono-quasicrystal The measurements were carried out in the temperature range from 290 K up to 1220 K for measuring frequencies between 0.1Hz and 10 kHz. A loss maximum of Debye type is observed at ≈ 700 K (2Hz) for both the I-phase and the bCo-phase, which is attributed to local rearrangement of point defects. The activation enthalpy of the peak of H = 1.9 - 2.4 eV is in the range of values obtained from tracer diffusion experiments. This indicates that local defect rearrangement and self diffusion are governed by the same atomic diffusion process.. A high temperature viscoelastic damping background is only observed in polycrystalline samples with H = 2.4 – 3 eV. The background is assigned to viscolealastic relaxation based on intergranular diffusion.

Inhibition Layer Breakdown by a Fast Diffusion Procedure of Zinc in Galvanized Coatings

Thick sheets of steel were galvanized in a bath containing Al additions. A Fe2Al5 layer is formed at the substrate steel sheet, which leads to a desirable transient inhibition of Fe-Zn reactions. Thus the more protective (eta) phase rich in zinc is favored. However an appreciable intergranular diffusion and a gradual formation of internal and surface oxide particles influence the growth and stability of the inhibition layer. The location of some oxide particles at the Fe2Al5 surface or inside of this layer, led to conclude that oxide particles might cause Fe-Zn outburst growths to form. This is because zinc diffuses along the oxide particle/Fe2Al5 interface. Moreover the mechanism of oxide formation causes a local depletion of the atoms concentration in the bath in the vicinity of the formed oxide. This in turn diminishes the probability of the formation of the Fe2Al5 layer. So the whole mechanism provides a fast diffusion bath for Zn, which reacts with Iron atoms forming Fe-Zn phases. The formation of the phases, were determined by XRD measurements (PHILIPS diffractometer CuKα radiation) while the dispersion of the elements was examined by SEM (20kV JEOL 840A equipped with an OXFORD ISIS 300 EDS analyzer.