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Application of Mechanical Activation in Synthesizing Multiferroic Pb(Fe1/2Nb1/2)O3 Powders

In the study, the method of high-energy powder milling - mechanical activation (MA) was used for synthesizing Pb(Fe_1/2Nb_1/2)O₃ (PFN) powders. For the purpose of comparing the influence of high-energy milling on PFN synthesis, two groups of powder samples were used. The first mixture consisting of simple oxide powders; the second one consisting of compound oxide powders. The obtained powders were subjected to structural analysis with the use of XRD and Mőssbauer spectroscopy. Tests revealed that during the process of high-energy milling of initial constituents a partial synthesis of PFN material phases occurs. By comparing the two methods of PFN synthesizing it may be stated that mechanical activation in the case of a simple oxide mixture (PFN1) is equally effective as for a compound oxide mixture (PFN2).

Abstract

We present the results of obtaining and investigations of (Pb_1-x Ba_x )((Zr_1-yTi_y) _1-zSn_z )O₃ (PBZTS) ceramics with x =const =0.03, y =const=0.02, z =0, 0.02, 0.04, 0.06 and 0.08. Investigated compositions are close to rhombohedral-orthorhombic morphotropic phase boundary. Ceramic samples have been obtained by conventional ceramic technology from oxides PbO, ZrO₂, TiO₂, SnO₂ and barium carbonate BaCO₃. The calcined powders were crushed and next pressed into discs and sintered free sintering (FS) method. For such obtained samples the following investigations have been done: EDS, XRD, microstructure of fractured samples, dielectric measurements, /’-/^hysteresis loops investigations at various temperatures.

This work reports on determination of the influence of passivation type of Ti15wt.%Mo implant alloy surface on its corrosion resistance in simulated body fluids. The alloy under investigation was subjected to natural self-passivation in air, and forced passivation by autoclaving in steam, boiling in 30 % solution of H₂O₂, and electrochemical passivation in 0.9 % NaCl solution. Resistance of the passivated Ti15Mo alloy to pitting corrosion was studied at 37ºC in 0.9 % NaCl solution using open circuit potential method, anodic polarization curves, and electrochemical impedance spectroscopy (EIS). Comparative estimation of the determined parameters of corrosion resistance revealed that the obtained passive layers improve anticorrosive properties of the tested alloy. Surface of the alloy subjected to passivation in steam autoclave reveals the highest protection against pitting corrosion. Anodic potentiodynamic curves showed that the Ti15Mo alloy after different passivation types of the surface is characterized by a lack of susceptibility to pitting corrosion up to potential of 9 V. Based on the EIS investigations, the thickness of the formed oxide layers (TiO₂, anatase) was determined to be in the range from 2.0 to 7.8 nm in dependence on the applied type of passivation. It was ascertained that electrochemical properties of the Ti15Mo alloy and possibility of its surface passivation using simple methods, make it an attractive material for use in biomedicine for long-term implants.

Evaluation of corrosion resistance of the self-organized nanotubular oxide layers on the Ti13Zr13Nb alloy, has been carried out in 0.9% NaCl solution at the temperature of 37ºC. Anodization process of the tested alloy was conducted in a solution of 1M (NH4)2SO4 with the addition of 1 wt.% NH4F. The self-organized nanotubular oxide layers were obtained at the voltage of 20 V for the anodization time of 120 min. Investigations of surface morphology by scanning transmission electron microscopy (STEM ) revealed that as a result of the anodization under proposed conditions, the single-walled nanotubes (SWNTs) can be formed of diameters that range from 10 to 32 nm. Corrosion resistance studies of the obtained nanotubular oxide layers and pure Ti13Zr13Nb alloy were carried out using open circuit potential, anodic polarization curves, and electrochemical impedance spectroscopy (EIS) methods. It was found that surface modification by electrochemical formation of the selforganized nanotubular oxide layers increases the corrosion resistance of the Ti13Zr13Nb alloy in comparison with pure alloy.

Abstract

Investigations on the surface modification of the Ti-6Al-4V alloy by plasma electrolytic oxidation are reported here. The oxidation process was carried out in a solution containing a zirconium silicate (ZrSiO₄) suspension and sodium hydroxide (NaOH). Anodising was realised at voltages in a range from 100 V to 250 V. It was found that the morphology of the sample surface did not change during the oxidation of the alloy at 100 V. Application of voltages higher than 100 V led to the incorporation of zirconium silicate into the formed oxide layer and to significant changes of the surface morphology.