Giaime Marongiu

Characterization of Nanocrystalline γ–Fe 2 O 3 Prepared by Wet Chemical Method

Homogeneous maghemite (γ–Fe 2 O 3 ) nanoparticles with an average crystal size around 5 nm were synthesized by successive hydrolysis, oxidation, and dehydration of tetrapyridino-ferrous chloride. Morphological, thermal, and structural properties were investigated by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and x-ray diffraction (XRD) techniques. Rietveld refinement indicated a cubic cell. The superstructure reflections, related to the ordering of cation lattice vacancies, were not detected in the diffraction pattern. Kinetics of the solid-state phase transition of nanocrystalline maghemite to hematite (α–Fe 2 O 3 ), investigated by energy dispersive x-ray diffraction (EDXRD), indicates that direct transformation from nanocrystalline maghemite to microcrystalline hematite takes place during isothermal treatment at 385 °C. This temperature is lower than that observed both for microcrystalline maghemite and for nanocrystalline maghemite supported on silica.

Diclofenac nanosuspensions: influence of preparation procedure and crystal form on drug dissolution behaviour.

The aim of this paper was to ascertain the role of drug crystalline form and preparation procedure in nanosuspension formulations in order to optimise dissolution properties of lipophilic, poorly soluble drugs, thus improving their oral bioavailability. The non-steroidal anti-inflammatory drug diclofenac acid (DCF), which is known to exist in different crystal forms, was chosen as a model drug. To this purpose, the influence of homogenization technique was studied by preparing several nanosuspensions with two different crystalline forms of the drug (DCF1 and DCF2). Particle size and size distribution, morphology, microstructure, and thermal behaviour of the different formulations were studied by photon correlation spectroscopy (PCS), scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC). Solubility studies of the bulk drug crystalline forms and dissolution experiments of nanosuspensions in comparison with different controls (bulk drug, physical mixtures, coarse suspensions) were carried out in different media: distilled water, simulated gastric fluid (SGF) and simulated intestinal fluid (SIF). Besides well known factors capable of affecting drug nanoparticle dissolution, results showed that drug dissolution rate in nanosuspensions is strongly affected by the drug solubility, which depends on the crystal form, and preparation procedure (high pressure homogenization process). Results demonstrated that this process partially transformed DCF2 in DCF1 while it did not have any effect on the DCF1 crystals.

Fe-Co-B amorphous alloy powder by chemical reduction

Fine boride powders, prepared by reactions between sodium or potassium borohydride and aqueous (or alcoholic) solutions of transition metal salts have long been known to be good catalysts for hydrogenation reactions. New interest around them has recently grown, because they were found to exhibit amorphous structure. Classical chemical reactions may thus offer a simple route to prepare amorphous metal powders, paralleling more sophisticated methods so far used to reach the same goal. To explore the potential of these reactions, we considered the system Fe-Co-B with the aim of examining the characteristics of the product obtained in the easiest way and without any particular precautions. The structure of the amorphous alloy appears to be different from that of materials with a similar Me/B ratio prepared via melt spinning.

The synthesis of nanocrystalline nickel boride powders by ball milling of elemental components

Solid state reaction induced by ball milling the elemental components has been investigated on Ni60B40 and Ni80B20 mixtures by means of transmission electron microscopy, X-ray diffraction and differential scanning calorimetry. The time evolution of the reaction is similar in the two samples, although slower in Ni80B20. Reaction begins with the formation of o-Ni3B and of a disordered phase. The final products are nanocrystalline o-Ni3B and unreacted nickel in Ni80B20 and nanocrystalline t-Ni2B in Ni60B40. Different milling conditions, tested on the Ni60B40 sample, do not modify the path but affect the rate of the solid state reaction.

Characterization of FeOOH nanoparticles and amorphous silica matrix in an FeOOH-Sio 2 nanocomposite

A nanocomposite with an FeOOH/SiO2 ratio equal to 17.7 wt% and the pertinent matrix, obtained by etching away the nanoparticles through reaction with hydrochloric acid, were investigated by XRD, TGA-DTA, heliostereopicnometry, BET, and TEM techniques. The study shows the presence in the nanocomposite of ferrihydrite nanoparticles phase with average dimensions around 4 nm. The FeOOH nanoparticles structure was analyzed by synchrotron X-ray diffraction data using the distribution difference curve method. The porous structure of the matrix resulting by etching away the nanoparticles differs significantly from that of a pure SiO2 sample obtained by hydrolysis of TEOS under the same operative conditions followed in the nanocomposite preparation.

Nanocrystalline iron–cobalt alloys supported on a silica matrix prepared by the sol–gel method

Abstract Co x Fe 1− x nanocrystals in a silica matrix were prepared by the sol–gel method. The influence of metal precursors was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. The influence of gel aging on porosity was determined with adsorption–desorption isotherms on N 2 at 77 K. Magnetic measurements were carried out on the composite samples. The magnetic properties are discussed.

Influence of boron content on the amorphization rate of Co–B mixtures by mechanical alloying

Amorphous cobalt-boron alloy powders have been prepared by a high energetic ball mill at room temperature starting from different Co/B ratios. They were characterized by means of x-ray diffraction, scanning and transmission electron microscopy, and differential scanning calorimetry. Ball milling of Co–B mixtures induces solid-state amorphization which becomes faster with increasing boron content. After maximum amorphization ball milling leads to crystallization of t -Co 2 B in all the binary samples.

Structural evolution in mechanical alloying of Co and B powders

X-ray diffraction and scanning electron microscopy were used to monitor the mechanical alloying of four different mixtures of cobalt and boron with atomic compositions Co50B50, Co67B33, Co75B25 and Co80B20, respectively. The process induces amorphization reactions depending on the boron content; an almost complete amorphization was reached for the Co67B33 and Co80B20 samples, where only minor traces of unreacted cobalt are present. Extended X-ray absorption fine structure data collected on the most amorphous sample confirmed the diffraction results. In all the samples, the formation of t-Co2B was detected.

A Comparative X-Ray Diffraction Study of Aqueous MnSO4 and Crystals of MnSO4·5H2O

Abstract X-ray single crystal analysis of MnSO4·5H2O shows that the manganese atoms are octahedrally coordinated by oxygen atoms, four of which belong to water molecules and two to sulphate groups. A model derived from the crystal structure was fitted to the X-ray scattering intensities from aqueous MnSO4. Good agreement with experimental data is achieved using a model in which Mn(H2O)6-z(OSO3)z+2-2z interacts with about ten water molecules and each sulphate ion with about seven water molecules.

Structural properties of amorphous powders prepared by chemical reduction

Abstract X-ray diffraction measurements were carried out to investigate some structural aspects of Fe Co B and Co B amorphous alloys prepared by chemical reduction of metal ions in aqueous solution.