G. Rosas

On the nature of quasicrystal phase transitions in AlCuFe alloys

Abstract In this investigation, a systematic study on the effects of the composition and annealed treatments in the formation of the AlCuFe icosahedral phase is carried out. The experimental results obtained from 30 different compositions under normal solidification methods and rapid solidification techniques show that the main driving force to the formation of the icosahedral phase is a cubic phase known in the past as the β phase. The β (AlCuFe) phase has a crystalline structure similar to the compound Al50Fe50. However, its lattice parameter is different from the parameter corresponding to the binary compound Al50Fe50, and it varies depending on the amount of copper. This gives rise to a cubic solid solution, the so-called β phase. The studied compositions were in the ranges of: Al(73–55 at.%), Cu(20–25 at.%) and Fe(10–15 at.%). Different structural and chemical characterization techniques were employed such as: X-ray diffractometry, scanning electron microscope (SEM) with EDS attachments, transmission electron microscopy (TEM) and differential thermal analysis (DTA) observations.

Structural and mechanical properties of the AlFe intermetallic alloy with Li, Ce and Ni additions

Microstructural and mechanical properties of AlFe intermetallic alloys with additions of Li, Ni, Ce and combinations of (Ce, Ni) and (Ce, Li) were obtained. The alloys were produced with normal casting techniques using SiC crucibles. Compression tests were carried out and some insights on the alloys mechanical properties are withdrawn. The main effect of these elements on the microstructure of the AlFe alloy is related with the improvements of the compressive ductility.

On the transformations of the ψ-AlCuFe icosahedral phase

Abstract In the present investigation, different alloy compositions close to the ternary composition values, where the icosahedral phase in AlFeCu is obtained, have been studied. The specimens were obtained using a rapid solidification technique with subsequent thermal treatments of 600°C, 700°C, 800°C and 900°C. The obtained specimens were characterized with X-ray diffraction patterns (XRD) and transmission electron microscopy (TEM). The experimental results show different transformations of the icosahedral phase to crystalline phases between 800°C and 700°C .The cubic β-phase is a solid solution which regulates the formation and decomposition of the ψ-Al 6 Cu 2 Fe phase to different crystalline phases such as the tetragonal (Al 7 Cu 2 Fe) and monoclinic (Al 13 Fe 4 ) phases.

Effect of the surfactant on the growth and oxidation of iron nanoparticles

Fe nanoparticles and branched nanostructures of iron oxide were synthesized by chemical reduction in aqueous phase. The mechanism of formation of iron oxides as a function of the amount of surfactant employed during the synthesis process was studied. Specifically Fe, Fe2O3, and Fe3O4 nanoparticles were obtained. The oxidation of Fe to Fe3O4 and finally to Fe2O3 was carried out by oxidative etching process, decreasing the amount of stabilizer agent. The structures obtained were characterized by high resolution (HRTEM) and scanning/transmission (STEM) electron microcopies, energy dispersive spectroscopy (EDS), and optical spectroscopy (UV-Vis and IR).

Effects of Minor Element Additions to the Nanocrystalline FeAl Intermetallic Alloy Obtained by Mechanical Alloying

Chemical, microstructural, and mechanical properties of nanocrystalline FeAl intermetallic alloys with Li, Ce, and Ni additions have been assessed. Mechanical alloying and sintering procedures were used to produce and consolidate the alloys. The sintering procedure was based on room temperature uniaxial pressing followed by annealing in air of the pressed specimens. The mechanically alloyed powders have a microstructure consisting of micrometer-size particles that contain FeAl intermetallic nanocrystals. The three minor additional elements form a solid solution with the B2 intermetallic structure of the FeAl alloy. Densification greater than 90% has been obtained. The hardness values are higher than those obtained from specimens produced with conventional casting procedures. High resolution transmission electron microscopy images showed clusters of less than 5 nm with well-defined structure corresponding to Fe 3 Al.

Synthesis and Characterization of Bifunctional α-Fe2O3-Ag Nanoparticles

The synthesis of α-Fe2O3-Ag bimetallic nanoparticles using a novel and simplified route is presented in this work. These hybrid nanoparticles were produced using a modification of the chemical reduction method by sodium borohydride (NaBH4). Fe(III) chloride hexahydrate (FeCl3·6H2O) and silver nitrate (AgNO3) as precursors were employed. Particles with semispherical morphology and dumbbell configuration were observed. High-resolution transmission electron microscopy (HRTEM) technique reveals the structure of the dumbbell-like α-Fe2O3-Ag nanoparticles. Some theoretical models further confirm the formation of the α-Fe2O3-Ag structures. Analysis by cyclic voltammetry reveals an interesting catalytic behavior which is associated with the combination of the individual properties of the Ag and α-Fe2O3 nanoparticles.

Synthesis of Ag Nanoparticles-Clinoptilolite Composite by Homogeneous and Heterogeneous Nucleation

In this study, a natural zeolite clinoptilolite-type was impregnated through homogeneous and heterogeneous nucleation with silver nanoparticles. The synthesis of Ag nanoparticles was carried out by chemical reduction of silver nitrate (AgNO3) with sodium borohydride (NaBH4). In the case of homogeneous nucleation, colloidal solution of Ag nanoparticles at concentrations of 1, 2 and 4 parts per million was added and magnetically mixed with the porous material. With respect to heterogeneous nucleation, a solution of clinoptilolite and silver nitrate (0.01 M) was prepared and stirred; subsequently, the reduction of Ag was possible due to the addition of an aqueous solution of sodium borohydride. For the structural characterization, transmission electron microscopy (TEM), X-ray diffraction (XRD) and infrared spectroscopy (IR) techniques were carried out. The results were compared and discussed in both types of nucleation.

High-Energy Ball-Milling of FeAl2 and Fe2Al5 Intermetallic Systems

In this study, FeAl2 and Fe2Al5 intermetallic alloys were prepared by conventional casting technique. In order to study their structural stability the alloys were subjected to high-energy ball milling process for 1, 2.5, 5 and 10 h. The structural and chemical characterizations were conducted by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and differential scanning calorimetry. After 10 h of milling, the experimental results indicated a phase transformation from FeAl2-triclinic phase to Fe2Al5-ortorrombic structure. This phase transformation is characterized by a change from low to high symmetry systems.

Spectroscopy Study of Silver Nanoparticles Produced by Chemical Reduction

In this study, Ag nanoparticles were synthesized using two chemical reduction agents; ethylene glycol and sodium borohydride. Different particle size distributions were obtained and characterized by transmission electron microscopy. Ag nanoparticles concentrations of 1, 2 and 4 parts per million (gmL-1) were prepared and studied by ultraviolet-visible spectroscopy (UV-Vis) and atomic absorption spectrophotometry (AAS). In the UV-Vis results a characteristic band at 420 nm were observed. However, when the concentration of silver decreased, a change in band intensity was detected. Atomic absorption spectrophotometry measurements from different solutions of Ag nanoparticles showed a linear behavior similar to the silver standard solution in the concentration range 1 to 4 mgL-1. However, up 4 mgL-1 concentrations, the slope of the calibration curve is increases when the concentration of Ag nanoparticles is increased too.

Analysis for the Sorption Kinetics of Ag Nanoparticles on Natural Clinoptilolite

The kinetic adsorption behavior of silver nanoparticles deposited on a natural zeolite from Oaxaca is presented. Theoretical models as Lagergren first-order, pseudo-second-order, Elovich, and intraparticle diffusion were employed and compared with experimental data obtained by atomic absorption spectrophotometry technique. Correlation factors of the order of 0.99 were observed. Analysis by transmission electron microscopy revealed that the silver nanoparticles were homogeneously distributed on the zeolite. Additionally, chemical characterization of the material was carried out through a dilution process with lithium metaborate. An average value of 9.3 in the Si/Al ratio was observed and related to the kinetic adsorption behavior of the zeolite.