The rail grease formulation effect in friction, wear, and grease loss due to centrifugal force was evaluated through pin on disc and free flow tests. Six greases were fully formulated so that the effects of the thickener and the base oil viscosity on grease performance could be isolated, since these greases have the same consistency and additive package but different base oil viscosities (50, 200, and 500 cSt) and thickener types (lithium and calcium). The results showed that: (a) lithium greases present lower friction but higher wear than calcium grease; (b) higher kinematic viscosity produces lower wear but higher friction regardless of the thickener type; (c) the critical speed at which grease is expelled from the disc increases with viscosity for lithium-thickened greases and does not depend on viscosity for calcium greases; and (d) lithium greases with high base oil viscosity suit best the wheel-rail interface lubrication, which was verified with the aid of a grease performance index proposed in the present work.

Lipophilic nanoparticles of magnetite (d≈10 nm) functionalized with stearic acid (MagNP) were tested as additive in modern engine oil with low viscosity and high additization. Its thermal and tribological properties were evaluate using TG/DTA and a high frequency reciprocating tribometer, respectively. All tests were performed with the neat oil and the oil+MagNP. The analysis showed that MagNP: i) improved thermal stability of the engine oil; ii) kept friction values lower and more stable; iii) drastically reduce wear marks; iv) improved the deposition of additives from the lubricating oil onto the worn surface.

Lipophilic magnetite nanoparticles (MagNP; d≈10nm) functionalized with stearic acid were synthetized and tested as additive in polyalphaolefin synthetic base oil (PAO8) in a model system. The thermal properties of the starting base oil and of the base oil mixed with nanoparticles were evaluated using TG/DTA under inert and oxidizing atmosphere. The frictional response of the lubricants was evaluated under a broad range of operating conditions at the boundary lubrication regime using a 10mm AISI 52,100 bearing steel ball against the flat face of an AISI H13 steel disc. The results showed that: i) MagNP improved the thermal stability of the base oil; ii) reduced the friction values, mostly during load step transition; iii) reduced significantly the wear marks.

Magnetic graphite materials (GMag) were prepared by adsorbing oleate coated magnetite nanoparticles (MagNP) on the exposed surfaces of graphite, in the powder form. The materials were characterized by SEM (scanning electron microscopy) and EDX (energy dispersive X-ray fluorescence), and their magnetic properties were probed with a SQUID (superconducting quantum interference device) magnetometer. By incorporating MagNP, the modified graphite became responsive to magnetic fields, either as a powder or liquid suspension, allowing to reflect white light and lasers, and to control the light beam transmission, simulating smart windows and optical displays.

We report on a new, promising nanotechnological approach for hydrometallurgy based on recyclable, chemically functionalized superparamagnetic nanoparticles. In this process, the metal ions (e.g. Cu2+) are captured by the nanoparticles and confined at the electrode surface by means of an external magnet. Due to the pre-concentration effect the electrodeposition process is greatly improved, yielding the pure metal in a much shorter time in comparison with the conventional electrodeposition process. After the electrolysis, the magnetic nanoparticles are ready to return to the process. The proposed strategy can advantageously be incorporated in hydrometallurgy, reducing the number of steps associated with complexation, organic solvent extraction, metal release and diffusional electroprocessing, leading to a more sustainable technology.

We propose the use of functionalized superparamagnetic nanoparticles for capturing, and transporting analytes, in association with an external miniature magnet to deposit such nanocarrier species at the electrode surface. This approach can be employed for the electroanalytical determination of chemical species capable of interacting with the nanoparticles, or in the opposite case, to block their response at the electrode surface. The concept was successfully demonstrated by using aminofunctionalized nanoparticles to block the discharge of hexacyanoferrate(II) ions, and to enhance the signals of aquapentacyanoferrate(II) ions via coordination to the surface amino groups. Selective analysis was also performed for silver ions, surpassing the stripping methods in terms of versatility and usefulness.

Mercury ions can be captured with superparamagnetic carbon powder substrates and transported to the electrode surface using an external miniature magnet. The magnetic carbon substrate is electronically conducting, and more than promoting efficient preconcentration of the element at the electrode, it increases the electrochemical surface area by forming an extended 3D structure in the presence of a magnetic field. The external magnet allows to perform direct electrochemical analysis, leading to a strong enhancement of the analytical signals for the reduction of the Hg(II) ions.

Thioredoxin (Trx1), a very important protein for regulating intracellular redox reactions, was immobilized on iron oxide superparamagnetic nanoparticles previously coated with 3-aminopropyltriethoxysilane (APTS) via covalent coupling using the EDC (1-ethyl-3-{3-dimethylaminopropyl}carbodiimide) method. The system was extensively characterized by atomic force microscopy, vibrational and magnetic techniques. In addition, gold nanoparticles were also employed to probe the exposed groups in the immobilized enzyme based on the SERS (surface enhanced Raman scattering) effect, confirming the accessibility of the cysteines residues at the catalytic site. For the single coated superparamagnetic nanoparticle, by monitoring the enzyme activity with the Ellman reagent, DTNB=5,5′-dithio-bis(2–15 nitrobenzoic acid), an inhibitory effect was observed after the first catalytic cycle. The inhibiting effect disappeared after the application of an additional silicate coating before the APTS treatment, reflecting a possible influence of unprotected iron-oxide sites in the redox kinetics. In contrast, the doubly coated system exhibited a normal in-vitro kinetic activity, allowing a good enzyme recovery and recyclability.

New routes for low cost production of functionalized magnetic nanoparticles (MagNP) have been pursued in this Thesis, by employing environmentally compatible chemicals and resources.The nanomaterials exhibited typical superparamagnetic behavior consistent with the presence of magnetic monodomains, revealing no hysteresis above 280 K, T b = 90 K at H = 500 Oe, and saturation magnetization as high as 90 emu g -1 .The synthetic procedures were carried out using biocompatible solvents derived from biodiesel of soybean and Brazilian mamona seeds, leading to substantial reduction of cost for large-scale production.The superparamagnetic nanoparticles were initially designed for capturing, transporting and recycling chemicals or drugs, including pollutants, catalysts and enzymes, using external magnets.They provide a green alternative strategy for conventional processes that make extensive use of solvents, generate too much waste, and proceeds through highly energetic demanding steps such as centrifugation, solvent extraction and high-pressure filtration.In our work, the MagNPs were appropriately modified for working in polar and non-polar media, employing for instance, amphiphilic species for interacting with Fe 3 O 4 using the available polar groups, and also with carbon surfaces by means of hydrophobic interactions.Accordingly, new superparamagnetic nanomaterials incorporating several types of materials carbon based.It was observed that the carbon materials containing 15 to 20% of magnetic nanoparticles could be completely removed from the media with the use of a magnet.In this way, the functionalized superparamagnetic nanoparticles proved useful for the removal of oil spills and of organic pollutants from industrial processing water, as well as for the capture, removal and recovery of metallic elements and organic species from the effluents.In addition, as a proof of concept, smart windows and displays were elaborated based on the modulation of the transmitted or reflected light by the external magnet.This work was sponsored by PETROBRÁS, and also covered missing, non-authorized aspects involved in two patent applications.Finally, an important consequence to be mentioned is the contribution of this project for launching new chemical routes towards sustainability, such as the development in this Laboratory, of green, magnetic nano-hydrometalurgy for processing and recycling strategic metals, and of the magnetic remediation of polluted environments using the functionalized nanomaterials.

Superparamagnetic nanoparticles previously modified with mercaptopropyltriethoxysilane were employed in this work as electrode modifiers, for direct use in the presence of an external miniature magnet, for the analysis of mercury ions from aqueous solutions, as well as from crude oil. After capturing the mercury ions, the nanoparticles were magnetically concentrated at the electrode surface. The nanoparticles coating exhibited a sharp electrochemical response, and the preconcentration effect led to a strong enhancement of the electrochemical signals. The in situ magnetic coupled electroanalysis was successfully demonstrated for mercury ions and confronted with parallel energy dispersive X-ray fluorescence measurements. Rather consistent results were observed for mercury ions either from aqueous solutions, as well as from the crude oil samples.