E. Mazario

Synthesis and characterization of CoFe2O4 ferrite nanoparticles obtained by an electrochemical method

Uniform size cobalt ferrite nanoparticles have been synthesized in one step using an electrochemical technique. Synthesis parameters such as the current density, temperature and stirring were optimized to produce pure cobalt ferrite. The nanoparticles have been investigated by means of magnetic measurements, Mössbauer spectroscopy, x-ray powder diffraction and transmission electron microscopy. The average size of the electrosynthesized samples was controlled by the synthesis parameters and this showed a rather narrow size distribution. The x-ray analysis shows that the CoFe(2)O(4) obtained presents a totally inverse spinel structure. The magnetic properties of the stoichiometric nanoparticles show ferromagnetic behavior at room temperature with a coercivity up to 6386 Oe and a saturation magnetization of 85 emu g(-1).

One-pot electrochemical synthesis of polydopamine coated magnetite nanoparticles

Herein a facile and versatile one step synthesis of magnetite nanoparticles coated with polydopamine is described. Magnetite nanoparticles are synthesized electrochemically by electrooxidation of iron in an aqueous medium in the presence of dopamine. The oxidative conditions and alkaline pH involved in the synthesis favor the self-polymerization of dopamine that adheres at the surface of the magnetic nanoparticles in a simultaneous process. It is shown that the size of the magnetite nanoparticles as well as the polydopamine coating can be controlled by varying the synthetic approach that is, adding dopamine at the beginning of the electrosynthesis, in the middle or at the end of the process. The particle size of the core varies between a few nanometers and 25 nm while the shell can reach thicknesses of up to ∼5 nm. The obtained hybrid nanoparticles were characterized by thermogravimetric analysis (TGA), infrared spectroscopy (FTIR), X-ray diffraction (XRD) and transmission electron microscopy (TEM). In addition, the magnetic measurements of the different obtained materials were carried out showing a variety of magnetic behaviors depending on the synthetic procedure.

Synthesis and structural characterization of ZnxFe3−xO4 ferrite nanoparticles obtained by an electrochemical method

A series of zinc ferrite nanoparticles were synthesized following a single-step electrochemical method in aqueous medium. This strategy allowed the control of both the size and chemical composition of the nanoparticles in an easy and reproducible manner by simply varying the intensity of the applied current. The obtained nanoparticles were morphologically and structurally characterized as a function of the particle size and the Zn content in the sample by X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma emission spectroscopy (ICP) and Raman microscopy. The formation of ZnxFe(3−x)O4 (x = 0.18–0.93) ferrite nanoparticles with crystal sizes in the range of 9 to 18 nm and with a homogeneous distribution of the Zn2+ cation in the crystalline structure was observed. However, following a thermal treatment, a migration of zinc cations was detected that led to the formation of two different crystalline phases, stoichiometric zinc ferrite and hematite. Raman microscopy revealed the formation of segregated micro-domains enriched within these crystalline phases. The study of the magnetic properties of the electro-synthesized ferrite nanoparticles with a homogeneous incorporation of Zn in the structure shows that the saturation magnetization and the coercively values are highly dependent on the chemical composition and crystal size.

Pitting corrosion and stress corrosion cracking study in high strength steels in alkaline media

Steel reinforcement in concrete is protected from corrosion by passivation due to the high alkalinity of the cement pore solution, but the presence of aggressive ions as Cl− could induce pitting corrosion processes thus decreasing the durability of the structure. This also occurs for prestressing concretes but the risk to suffer pitting corrosion in presence of aggressive ions, and hence stress corrosion cracking (SCC), increases due to the external mechanical load. The study of the corrosion processes by classical methods involves the determination of pitting potential (Epit) or the polarization resistance monitoring during long periods (icorr). However, the large number of parameters, which could potentially influence the determination of the Epit or the icorr values, result in a great variety of results in literature. The present study proposes a simple and reliable method to evaluate the susceptibility to suffer pitting corrosion process and stress corrosion cracking by the induction of pitting corrosion process by cyclic voltammetry. The pitting corrosion intensity is evaluated by means of the charge during the corrosion process, and related with the weight loss and the decrease of the mechanical properties of the steel under external load. The results show a linear and a volcano trend when pitting corrosion process and stress corrosion cracking are respectively evaluated.