Gerardo Rosas - Academia.edu (original) (raw)

Papers by Gerardo Rosas

Research paper thumbnail of Mechanical alloying synthesis of carbon nanotubes in the presence of AlFe small clusters

Materials Letters, 2007

Carbon nanotubes and small metallic particles (1–3 nm) have been obtained using mechanical alloyi... more Carbon nanotubes and small metallic particles (1–3 nm) have been obtained using mechanical alloying techniques. High resolution electron microscope (HREM) techniques have been employed for the structural characterization of the small metallic particles and for the carbon multiwalled nanotubes. Theoretical simulations based on molecular dynamics and quantum mechanic calculations have been used to get insights on the experimental structural results.

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

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2003

Microstructural and mechanical properties of AlFe intermetallic alloys with additions of Li, Ni, ... more 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 Compression tests were carried out and some insights on the alloys mechanical properties are withdrawn.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

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

Materials and Manufacturing Processes, 2005

Chemical, microstructural, and mechanical properties of nanocrystalline FeAl intermetallic alloys... more 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 ...

Research paper thumbnail of Tensile Strength and Ductility of Al-MT (MT = Fe, Ni) Intermetallic Alloys

Materials and Manufacturing Processes, 2007

In this work, FeAl and NiAl intermetallic alloys were produced by conventional casting using SiC ... more In this work, FeAl and NiAl intermetallic alloys were produced by conventional casting using SiC crucibles. Li and Ni elements with 1, 3, and 5% were added to the AlFe intermetallic compound. In the case of NiAl intermetallic, the alloy' composition was based on (Ni55Fe5)Al with additions of 1, 3, and 5% of Li. After casting, the ingots were homogenized

Research paper thumbnail of Iron nanoparticles produced by high-energy ball milling

Journal of Nanoparticle Research, 2007

In this investigation, the chemical and structural characteristics of Fe nanoparticles synthesize... more In this investigation, the chemical and structural characteristics of Fe nanoparticles synthesized by high-energy ball milling have been explored. After the milling process the nanoparticles were collected using a magnetic field. The structure, morphology and composition of the powders were obtained using high-resolution electron microscopy. HREM images confirmed the nanoparticles’ presence with approximately 2–4 nm in size. It was found that using this method allowed the formation of nanoparticles in a smaller size range than other synthesis methods. Also, it was confirmed by HREM images that the obtained nanoparticles were mainly of the fcc nature and some of them of the MTP type.

Research paper thumbnail of Room Temperature Mechanical Properties of Fe 3 Al Intermetallic Alloys with Li and Ni Additions

Journal of Materials Engineering and Performance, 2009

This work analyzes the effect of very small additions of Li and Ni on the mechanical properties o... more This work analyzes the effect of very small additions of Li and Ni on the mechanical properties of the Fe72Al28 intermetallic alloy, close to the Fe3Al ratio. Hardness and tensile strength at room temperature were analyzed for the cast Fe3Al intermetallic alloys as a function of Li and Ni additions. For this purpose, high-purity raw materials were melted in an open induction furnace into a SiC crucible and the liquid alloys were poured into sand moulds to directly get tensile test-shaped specimens to minimize machining. Mechanical tests were carried out in the as-cast condition as well as after a homogenization heat treatment at 400 °C for 120 h. The obtained microstructure was characterized by XRD and SEM. Results show an increase in ductility, particularly when Li was added.

Research paper thumbnail of Structural analysis and shape-dependent catalytic activity of Au, Pt and Au/Pt nanoparticles

Materia-rio De Janeiro, 2008

Metallic nanoparticles of Au, Pt and Pt/Au have been synthesized using a chemical reduction appro... more Metallic nanoparticles of Au, Pt and Pt/Au have been synthesized using a chemical reduction approach. The structural characterization of these metallic nanoparticles has been carried out using conventional transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HR-TEM) techniques. HR-TEM images of Pt nanoparticles reveal their fcc-like structures, in the [103] and [011] orientations. However, in case of Au, the main structures are fcc-like and decahedral morphologies with five-fold symmetry axes. The structure of the gold nanoparticles was verified through their theoretically-simulated images, using a multislice approach of the dynamical theory of electron diffraction. These small particles have been used as electrocatalysts in Nafion membranes for fuel cell applications. The electrochemical characterization of the membranes shows that the Pt dispersion gives best performance for fuel cell applications.

Research paper thumbnail of Synthesis of gold nanoparticles with different atomistic structural characteristics

Materials Characterization, 2007

A chemical reduction method was used to produce nanometric gold particles. Depending on the conce... more A chemical reduction method was used to produce nanometric gold particles. Depending on the concentration of the main reactant compound different nanometric sizes and consequently different atomic structural configurations of the particles are obtained. Insights on the structural nature of the gold nanoparticles are obtained through a comparison between digitally-processed experimental high-resolution electron microscopy images and theoretically-simulated images obtained with a multislice approach of the dynamical theory of electron diffraction. Quantum molecular mechanical calculations, based on density functional theory, are carried out to explain the relationships between the stability of the gold nanoparticles, the atomic structural configurations and the size of nanoparticles.

Research paper thumbnail of Mechanical alloying synthesis of carbon nanotubes in the presence of AlFe small clusters

Materials Letters, 2007

Carbon nanotubes and small metallic particles (1–3 nm) have been obtained using mechanical alloyi... more Carbon nanotubes and small metallic particles (1–3 nm) have been obtained using mechanical alloying techniques. High resolution electron microscope (HREM) techniques have been employed for the structural characterization of the small metallic particles and for the carbon multiwalled nanotubes. Theoretical simulations based on molecular dynamics and quantum mechanic calculations have been used to get insights on the experimental structural results.

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

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2003

Microstructural and mechanical properties of AlFe intermetallic alloys with additions of Li, Ni, ... more 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

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

Materials and Manufacturing Processes, 2005

Chemical, microstructural, and mechanical properties of nanocrystalline FeAl intermetallic alloys... more 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 ...

Research paper thumbnail of Tensile Strength and Ductility of Al-MT (MT = Fe, Ni) Intermetallic Alloys

Materials and Manufacturing Processes, 2007

In this work, FeAl and NiAl intermetallic alloys were produced by conventional casting using SiC ... more In this work, FeAl and NiAl intermetallic alloys were produced by conventional casting using SiC crucibles. Li and Ni elements with 1, 3, and 5% were added to the AlFe intermetallic compound. In the case of NiAl intermetallic, the alloy' composition was based on (Ni55Fe5)Al with additions of 1, 3, and 5% of Li. After casting, the ingots were homogenized

Research paper thumbnail of Iron nanoparticles produced by high-energy ball milling

Journal of Nanoparticle Research, 2007

In this investigation, the chemical and structural characteristics of Fe nanoparticles synthesize... more In this investigation, the chemical and structural characteristics of Fe nanoparticles synthesized by high-energy ball milling have been explored. After the milling process the nanoparticles were collected using a magnetic field. The structure, morphology and composition of the powders were obtained using high-resolution electron microscopy. HREM images confirmed the nanoparticles’ presence with approximately 2–4 nm in size. It was found that using this method allowed the formation of nanoparticles in a smaller size range than other synthesis methods. Also, it was confirmed by HREM images that the obtained nanoparticles were mainly of the fcc nature and some of them of the MTP type.

Research paper thumbnail of Room Temperature Mechanical Properties of Fe 3 Al Intermetallic Alloys with Li and Ni Additions

Journal of Materials Engineering and Performance, 2009

This work analyzes the effect of very small additions of Li and Ni on the mechanical properties o... more This work analyzes the effect of very small additions of Li and Ni on the mechanical properties of the Fe72Al28 intermetallic alloy, close to the Fe3Al ratio. Hardness and tensile strength at room temperature were analyzed for the cast Fe3Al intermetallic alloys as a function of Li and Ni additions. For this purpose, high-purity raw materials were melted in an open induction furnace into a SiC crucible and the liquid alloys were poured into sand moulds to directly get tensile test-shaped specimens to minimize machining. Mechanical tests were carried out in the as-cast condition as well as after a homogenization heat treatment at 400 °C for 120 h. The obtained microstructure was characterized by XRD and SEM. Results show an increase in ductility, particularly when Li was added.

Research paper thumbnail of Structural analysis and shape-dependent catalytic activity of Au, Pt and Au/Pt nanoparticles

Materia-rio De Janeiro, 2008

Metallic nanoparticles of Au, Pt and Pt/Au have been synthesized using a chemical reduction appro... more Metallic nanoparticles of Au, Pt and Pt/Au have been synthesized using a chemical reduction approach. The structural characterization of these metallic nanoparticles has been carried out using conventional transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HR-TEM) techniques. HR-TEM images of Pt nanoparticles reveal their fcc-like structures, in the [103] and [011] orientations. However, in case of Au, the main structures are fcc-like and decahedral morphologies with five-fold symmetry axes. The structure of the gold nanoparticles was verified through their theoretically-simulated images, using a multislice approach of the dynamical theory of electron diffraction. These small particles have been used as electrocatalysts in Nafion membranes for fuel cell applications. The electrochemical characterization of the membranes shows that the Pt dispersion gives best performance for fuel cell applications.

Research paper thumbnail of Synthesis of gold nanoparticles with different atomistic structural characteristics

Materials Characterization, 2007

A chemical reduction method was used to produce nanometric gold particles. Depending on the conce... more A chemical reduction method was used to produce nanometric gold particles. Depending on the concentration of the main reactant compound different nanometric sizes and consequently different atomic structural configurations of the particles are obtained. Insights on the structural nature of the gold nanoparticles are obtained through a comparison between digitally-processed experimental high-resolution electron microscopy images and theoretically-simulated images obtained with a multislice approach of the dynamical theory of electron diffraction. Quantum molecular mechanical calculations, based on density functional theory, are carried out to explain the relationships between the stability of the gold nanoparticles, the atomic structural configurations and the size of nanoparticles.