Mara Carolina do Carmo Paresque

Hysteresis Modeling of Bonded Anisotropic Ferrite Magnets

The modeling of hysteresis curves of bonded ferrite magnets is discussed. Hysteresis of anisotropic magnets were calculated according to the Stoner-Wohlfarth Model, for the cosn (theta) distribution. The crystallographic texture has significant effect on the hysteresis curve. Two different samples were examined, one isotropic and another anisotropic. The anisotropy field of strontium ferrite magnets was determined to be 19.5 kOe. The Mr/Ms ratio of the anisotropic bonded magnet was estimated as 0.8.

Study of the Effects of SiO2 Nanoparticles Concentration on the TiO2 Nanoparticles Suspensions Stabilization

TiO2 nanoparticles (NPTiO2) suspensions are in several ecosystems and residue treatment processes or disposal systems due to their large industrial use and handling. The interactions of the NPTiO2 with NPSiO2 have special interest due to their strong ability to maintain high TiO2 nanoparticles concentration in suspension and promote nanoparticles clustering. These characteristics are used either in cleaning systems or in production of nanoparticles solution for several applications in the food industry or medicine. In this study, suspensions of NPTiO2 and NPSiO2 are synthetized and their stabilizations are discussed. A base TiO2 nanoparticles suspension was synthetized and the initial concentrations of SiO2 nanoparticles (NPSiO2) were changed in order to determine the effects of presence of SiO2 nanoparticles on the stabilization and clustering size. Zeta potential and concentrations measurements were carried out throughout the time and correlated with the initial concentrations of the base suspensions. In this study, the concentrations, zeta potential and pH are measured to estimate the stability of the suspensions. The clustering size, obtained by nanoparticle tracking analysis (NTA), are also monitored and discussed. Results of column soil experiments are discussed and compared under similar conditions with literature data.

Magnetite Nanoparticles Study Applied to Magnetic Hyperthermia Treatment

The functionalization of superparamagnetic iron oxide (SPIO) nanoparticles with bioactive molecules enables new applications of these nanomaterials due to their magnetic properties, which is affected by the surface coating of the nanoparticles. In this work, Fe3O4 nanoparticles type / core layer were synthesized by co-precipitation wet method and coated with a polymer mixture of polyethylene glycol (PEG). It was performed a study about duration in encapsulation of nanoparticles in their final size in order to get different thickness of coated layer and varied coating properties. With this study was expected to obtain different thicknesses and thus the coating properties. Five samples were synthesized according to the same procedure and amount of reactants used synthetic sequence for all samples, only varying the time spent by each sample coating process with polyethylene glycol. The different times for the coating samples were 10 minutes, 20 minutes, 30 minutes, 50 minutes and finally 60 minutes. The nanoparticles were characterized by Nanosight, TGA and DSC techniques. The results showed that the particle size suffers an increase during the first 30 minutes of duration of the coating step and then stabilizes.