Nelcy Della Santina Mohallem

Preparation of a Ferrofluid Using Cyclodextrin and Magnetite

Um ferrofluido foi obtido a partir da magnetita e da b-ciclodextrina, com a formacao de um complexo de inclusao. A caracterizacao fisico-quimica do complexo magnetita: b-ciclodextrina foi realizada atraves de espectroscopia de absorcao na regiao do infravermelho com transformada de Fourier, difracao de raios X, analise termica (TG/DTA), microscopia eletronica de transmissao (TEM) e espectroscopia de absorcao atomica. E a primeira vez que se relata na literatura a formacao de um complexo de inclusao de um oxido metalico em ciclodextrinas

Sintering studies of hydrothermal NiZn ferrites.

The isothermal sintering behavior of submicrometer-sized (< 50 nm) powders of Ni0.38Zn0.53Fe2.09O4, prepared by hydrothermal process, was investigated under different sintering conditions. The powders were characterized by chemical analysis, energy-dispersive spectrometry (EDS), X-ray powder diffraction and scanning electron microscopy. The powders were compacted uniaxially with polyvinylalcohol and sintered at different times and temperatures, under constant heating and cooling rates. The characterization of the ceramic bodies was conducted by X-ray diffraction, optical and scanning electron microscopy, helium picnometry and EDS. The investigations showed high density ferrites with different porosity and microstructures depending on the sintering conditions. The results have been explained in terms of a qualitative model, which indicates the relative influence of the densification and grain growth rates.

Solid-State Sintering of Hydrothermal Powders: Densification and Grain Growth Kinetics of Nickel–Zinc Ferrites

The hydrothermal process was employed to produce single-phase submicrometric NiZn ferrites. The materials were sintered in air at different temperatures and times (1100 to 1400°C, 5 to 240 min). After sintering, highly dense ceramic bodies with different microstructures were obtained. X-ray diffraction, helium pycnometry, nitrogen adsorption technique, and optical and scanning electron microscopy were used to determine the microstructural parameters of the samples. The modeling of the sintering process demonstrates a crossover between the densification mechanisms from grain boundary diffusion to lattice diffusion with increasing sintering temperature. It is also shown that, in the final-stage sintering, the grain growth kinetics is controlled by pore drag.

Nanocrystalline Titanium Oxide thin Films Prepared by Sol-Gel Process

Crystalline films of pure titanium oxide have been prepared on soda lime slide glasses by sol-gel process and dip-coating. The definition of various parameters such as chemical concentration, viscosity, catalyst type and withdrawal speed led to the preparation of transparent, crystalline and adherent coatings with hydrophobic characteristics. Their crystalline structure was evaluated as anatase phase by low angle X-ray diffraction. Thicknesses were measured by perfilometry, and the refractive indices were determined from transmittance spectrum taking into consideration the layers deposited onto the two sides of the substrate. Porosity was also estimated by UV-visible spectroscopy by using the Lorentz - Lorenz equation. The average grain size was evaluated by atomic force microscopy. The thicker and denser films presented hydrophobicity, which decreased when the film porosity increased.

Characterization and catalytic activity studies of sol–gel Co–SiO2 nanocomposites

Abstract Silica embedded with transition metals exhibits adequate properties for applications in catalysis, sensors and optics. Cobalt–silica (Co–SiO 2 ) nanocomposites were prepared by the sol–gel method and thermally treated at 700, 900, 1100 and 1250 °C. Characterization of the samples was performed by XRD and BET nitrogen adsorption. The performance of the nanocomposites was investigated by catalysis reactions of oxidation. These catalysts were found to be recyclable showing a catalytic activity even after a third recovering. The results indicate that thermal treatment of sol–gel nanocomposites at temperatures higher than 900 °C is essential for the preparation of active heterogeneous catalysts.

A comparison of TEM and DLS methods to characterize size distribution of ceramic nanoparticles

The accuracy of dynamic light scattering (DLS) measurements are compared with transmission electron microscopy (TEM) studies for characterization of size distributions of ceramic nanoparticles. It was found that measurements by DLS using number distribution presented accurate results when compared to TEM. The presence of dispersants and the enlargement of size distributions induce errors to DLS particle sizing measurements and shifts its results to higher values.

Influence of Drying on the Characteristics of Zinc Oxide Nanoparticles

The recent growth in the field of porous and nanometric materials prepared by non-conventional processes has stimulated the search of new applications of ZnO nanoparticulate. Zinc oxide is an interesting semiconductor material due to its application on solar cells, gas sensors, ceramics, catalysts, cosmetics and varistors. In this work, the precipitation method was used followed by controlled and freezing drying processes. The materials obtained were thermally treated at various temperatures. The influence of temperature on structural, textural, and morphological properties of the materials was studied by powder X-ray diffraction, infrared spectroscopy, scanning electron microscopy, nitrogen adsorption, and thermal analysis. The characteristics of both materials were compared.

Nanometric powders and sintered ceramics studied by atomic force microscopy

Atomic force microscopy, as well as the Brunauer, Emmett, and Teller technique and x-ray diffraction, was used to analyze ultrafine NiZn ferrite powders hydrothermally synthesized at 200 °C, for 5 h. The particle sizes, measured through AFM images acquired from the surface of pressed powders, were 52 ± 6 nm, which were higher than those obtained by the other techniques. The particles were monodispersed in size and approximately spherical, meeting the requirements for the production of high density sintered components. The observations performed on ceramic bodies sintered at different conditions (1100–1400 °C, 5 to 240 min) showed necks characteristic of the early stages of sintering (1100 °C) and the expected pore curvature evolution (1400 °C) with sintering time in the final stage of the sintering process. Using a straightforward sample preparation technique, AFM proved to be a powerful tool for direct analysis of ceramic powder particles on the nanometric scale and sintered ceramics at different sintering stages.

Magnetic nanocomposite thin films prepared by sol-gel process

Cobalt ferrite composite thin films, CoFe2O4/SiO2, were prepared by sol-gel process, using tetraethylorthosilicate (TEOS) as a precursor for silica, and metallic nitrates as precursors for ferrite. The obtained dip-coated films thermally treated at 550, 750, and 950 oC were transparent, homogeneous and adherent. Their magnetic properties were measured from 2.5 K to 300 K using a SQUID magnetometer. Superparamagnetic behaviour was observed at room temperature and below a blocking temperature appears with coercivity values increasing with annealing temperature.

Self-assembled organic–inorganic magnetic hybrid adsorbent ferrite based on cyclodextrin nanoparticles

Summary Organic–inorganic magnetic hybrid materials (MHMs) combine a nonmagnetic and a magnetic component by means of electrostatic interactions or covalent bonds, and notable features can be achieved. Herein, we describe an application of a self-assembled material based on ferrite associated with β-cyclodextrin (Fe-Ni/Zn/βCD) at the nanoscale level. This MHM and pure ferrite (Fe-Ni/Zn) were used as an adsorbent system for Cr3+ and Cr2O7 2− ions in aqueous solutions. Prior to the adsorption studies, both ferrites were characterized in order to determine the particle size distribution, morphology and available binding sites on the surface of the materials. Microscopy analysis demonstrated that both ferrites present two different size domains, at the micro- and nanoscale level, with the latter being able to self-assemble into larger particles. Fe-Ni/Zn/βCD presented smaller particles and a more homogeneous particle size distribution. Higher porosity for this MHM compared to Fe-Ni/Zn was observed by Brunauer–Emmett–Teller isotherms and positron-annihilation-lifetime spectroscopy. Based on the pKa values, potentiometric titrations demonstrated the presence of βCD in the inorganic matrix, indicating that the lamellar structures verified by transmission electronic microscopy can be associated with βCD assembled structures. Colloidal stability was inferred as a function of time at different pH values, indicating the sedimentation rate as a function of pH. Zeta potential measurements identified an amphoteric behavior for the Fe-Ni/Zn/βCD, suggesting its better capability to remove ions (cations and anions) from aqueous solutions compared to that of Fe-Ni/Zn.