Lilian Ferreira de Senna

Preparation of composite materials containing iron in a cross-linked resin host based on styrene and divinylbenzene

Iron composite materials based on styrene/divinylbenzene network hosts were produced using aqueous suspension polymerization. The effects of different kinds of porogen agent, toluene, toluene/n-heptane mixture or a toluene solution of polyphenyleneoxide on the bulk density, swelling in toluene and ferromagnetic properties of these materials were evaluated. The specific area and average porous diameter of network resins were characterized by BET and BJH methods, while the iron content was determined by atomic absorption spectrometry. The morphology of the composites was studied by both optical microscopy and scanning electron microscopy with energy dispersive X-ray analysis. All the spherical beads, irrespective of their sizes, have agglomerated iron particles located only on their surface. The particles have exhibited ferromagnetic behavior, with a coercivity of 328.69 Oe. The porogen agents used affect the iron particle distribution on the bead surfaces.

Influence of cathodic current density and mechanical stirring on the electrodeposition of Cu-Co alloys in citrate bath

Cathodic polarization curves of Cu-Co alloys were galvanostatically obtained on a platinum net, using electrolytes containing copper and cobalt sulfates, sodium citrate and boric acid (pH values ranging from 4.88 to 6.00), with different mechanical stirring conditions. In order to evaluate quantitatively the influence of the applied current density and the mechanical stirring on the cathodic efficiency, the alloy composition for the Cu-Co alloy deposition process, and the average deposition potential, an experimental central composite design 22 was employed, and three current density intervals (0.11 to 0.60, 0.50 to 1.98 and 2.44 to 9.94 mA.cm-2) were chosen from the polarization curves for this purpose. The results indicated that the current density (mainly in the range between 0.11 and 0.60 mA.cm-2) affected significantly all the studied variables. In the intermediate range (0.50 to 1.98 mA.cm-2), only the average potential was influenced by the current density. On the other hand, the mechanical stirring had a significant effect only on the copper content, for both the lowest (0.11 to 0.60 mA.cm-2) and the highest current density range (2.44 to 9.94 mA.cm-2). Indeed, in the last range, none of the studied deposition parameters presented significant influence on the studied variables, except for the copper content. This could probably be explained by the direct incorporation of Cu-Citrate complexes in the coating, which was enhanced at high current values.

Corrosion evaluation of orthodontic wires in artificial saliva solutions by using response surface methodology

and response surface methodology. The open circuit potential (OCP) was measured over the same period of time. Polarization curves and morphological analysis of the wires before and after the corrosion experiments were also carried out. The results showed that corrosion of the studied metal alloys depended on a combination among saliva pH, the exposition time, and the concentration of F - ions in the solution. The critical condition was observed for Ni-Ti wires at pH = 3.0, and high concentration of F - ions, causing a decrease in the OCP values and an increase in Ni dissolution and corrosion current density.

Hardness analysis and morphological characterization of copper-zinc alloys produced in pyrophosphate-based electrolytes

In this work, copper-zinc alloy coatings on mild steel substrates were obtained in nontoxic pyrophosphate-based electrolytes, at room temperature and under continuous current. The effects of bath composition and current density on the hardness of the coatings, as well as on their morphologies, were evaluated. The results showed that the electrolyte composition, and the use of stress relieving additives strongly influence the hardness of the coatings, while the current density directly affect their morphology. Hence, for a current density of 116 A/m2, copper-zinc alloy deposits with no pores or cracks were produced in a pyrophosphate-based electrolyte, especially when allyl alcohol was added to the solution.

Electrodeposition of Cobalt Rich Zn-Co alloy Coatings from Citrate Bath

Zn-Co alloy coatings were produced on carbon steel, at room temperature, from citrate baths (0.100 mol L-1) containing [Zn2+]= [Co2+] = 0.05 mol L-1. Coatings with %m/m Co > %m/m Zn were observed under all deposition conditions, except for I = 10 A m-2. As the current density (I) was increased, a significant decrease (p<0.05) in %m/m Zn was noted, and the highest value of % m/m Co was observed at 80 A m-2. The Co-rich coatings presented refined microstructure, with small grain sizes. The smallest Icorr of the studied substrate/coatings systems, 2.4 µA cm-2, was obtained at I = 10 A m-2. Under these conditions, the coatings contained ~ 30 % m/m Co and 70 % m/m Zn and only the γ-ZnCo phase was obtained. The Icorr found in the present work is smaller than those usually found in the literature for Zn-Co coatings with small Co content.

Statistic evaluation of cysteine and allyl alcohol as additives for Cu-Zn coatings from citrate baths

In the present work, cysteine and allyl alcohol were added to citrate baths as additives to Cu-Zn coatings on steel substrates. In order to verify the effects of the deposition parameters (current density, mechanical stirring speed, and additives) on the coating composition, electrochemical behavior, morphology, and microstructure properties of Cu-Zn coatings, the electrodeposition of the alloy was carried out using an experimental composite design 23, in which these parameters were considered the entry variables and the measured properties were the response variables. The confidence level was 95% and the results were shown as response surface diagrams. It was possible to verify that the current density affected the zinc content in the coating, while the coating produced from cysteine-contained bath presented the worse anticorrosive performance. In a general way, it was possible to observe that the studied parameters affected the morphology, grain size, and the electrochemical behavior of these coatings, although only a few response variables were statistically influenced by them.

Experimental Design and Response Surface Analysis as Available Tools for Statistical Modeling and Optimization of Electrodeposition Processes

Electrodeposition, also called electroplating, is one of the most commonly used methods for metal and metallic-alloy film preparation in many technological processes. This method is generally considered an economically interesting and easily controlled process to protect and enhance the functionality of parts used in diverse industries (home appliances, jewelry, automotive, aircraft/aerospace, and electronics) in both decorative and engineering applications. It promotes the appearance, extends the life, and improves the performance of materials and products in different media (Schwartz, 1994; Oriňakova et al., 2006).

Analysis of networks based on styrene and divinylbenzene containing iron anchored using variable pressure scanning electron microscopy

There is great demand for the development of composite materials containing small metal or metal oxides particles, owing to their variable properties and wide application. However, microscopic evaluation of these materials using high‐vacuum scanning electron microscopy is difficult because the samples must undergo a series of preparation steps to reach a high image quality and to avoid becoming shrunk inside the microscope vacuum chamber. Thus, in this study, we used variable pressure scanning electron microscopy to evaluate the morphology and iron distribution on the surface of magnetic microspheres based on poly(styrene‐co‐divinylbenzene). These materials were obtained by suspension copolymerization of styrene and divinylbenzene in the presence of fine iron particles. Energy‐dispersive X‐rays were also used to analyse distribution of the iron particles. The results indicate that, under the conditions used, magnetic microspheres with a relatively narrow size distribution were formed. Moreover, the micrographs show that agglomerated iron particles appeared only on the microsphere surface.

AFM Characterization of Composite Materials Containing Iron in a Resin Host Based on Styrene and Divinylbenzene

The development of composite materials containing small metal or metal oxides particles has attracted a great deal of attention for their interesting chemical, physical and magnetic properties, providing their use for several technological applications. However, it is necessary that a complete evaluation of the morphological features of these composite be performed and correlated to the above mentioned properties. Therefore, the aim of this work was to use VP-SEM and AFM to investigate the morphology and the phase difference of composite materials based on styrene (STY) and divinylbenzene (DVB), containing iron particles. MFM analysis was also carried out to verify the magnetic properties of surface iron particles.

A review of Corrosion Resistance Nanocomposite Coatings

The deterioration of materials, particularly metals, under the influence of electrochemical corrosion is a high cost problem faced by nearly all industries. The reduction of corrosion processes and the prevention of future problems require a detailed knowledge of these processes and of the strategies to avoid them. In this context, it is essential to use method‐ ologies that may prevent the electrochemical deterioration of materials as well as monitor their performance in aggressive environments. Among them, it is possible to cite the use of functional coatings, particularly nanocomposite coatings. Therefore, this chapter pro‐ poses a review concerning the production of nanocomposite coatings with anticorrosive application obtained by electrodeposition technique (electrochemical codeposition). The production of such coatings is in agreement with the current needs of innovation, which drives a requirement for scientific advancement and the need for fundamental research. In this context, nanocomposite coatings with anticorrosive properties promote changes in metal surfaces, creating new materials with improved characteristics compared to those originally observed and maintaining the integrity of these surfaces.