Materials Science Forum Vols. 783-786

Abstract: Using the mixed powders containing gas-atomized powders of metallic glassy alloys (Cu₅₀Zr₄₅Al₅, Fe₇₃Si₇B₁₇Nb₃, Ni_52.5Nb₁₀Zr₁₅Ti₁₅Pt_7.5) blended with high-conductive Cu particulates, we produced bulk metallic glassy alloy composites with high strength and high electrical conductivity, as well as with enhanced plasticity and satisfying large size requirements by a spark plasma sintering process. In this paper we present and review our research results on the fabrication and properties of the bulk glassy alloy composites by the spark plasma sintering process.

Abstract: In recent years, bulk metallic glasses (BMGs) have received considerable attention due to their unique mechanical properties. However, the deformation of BMGs is highly localized in a few shear bands so that many of them exhibit poor plasticity. As such, more and more researchers have focused on improving the plasticity by in-situ or ex-situ introducing of nanoor micro-scale crystalline phases into the metallic glassy matrix in order to formation of multiple shear bands.

Abstract: Good crystalline of ATO thin films is necessary to improve the electrical and optical properties. In this paper, ATO thin films were fabricated using PLD method at high temperature of 550 °C, and the effect of laser energy density on the microstructure, electrical property and optical property of the ATO films is discussed. The results suggest that ATO films show good crystalline when deposited at high temperature of 550 °C. Both the electrical and optical properties have been enhanced with the increasing of laser energy density. When the laser energy density is 5.4 J/cm², the lowest resistivity of ATO thin film is obtained with the value of 6.52×10^-4 Ω·cm and the average optical transmittances is 82.0 %.

Abstract: The stricter environmental regulations impose a drastic reduction of vehicles emissions and a longer durability of the automotive catalyst. The studies of the catalyst evolution in real conditions are very expensive. It is interesting to elaborate an ageing process to well simulate the real conditions of the automotive catalyst ageing at the laboratory scale. Thermal, chemical and mechanical effects can cause degradations of the catalytic performances. Thermal ageing is the result of high temperature that surges in the catalytic converters. Chemical ageing is due to phosphorus, zinc, magnesium, calcium or sulfur originating from either engine oil additives or fuel contaminants. Mechanical ageing (cracks and detachment) is the consequence of thermal and chemical ageing (thermal and textural stresses). Understanding the formation of crack patterns and spalling of thin films is challenging in fracture mechanics. The need for two conditions, one involving energy and the other one stresses, has recently been shown. The stress condition defines a threshold below which the pattern formation is inhibited. As this threshold is not reached, the energy accumulates. Then, at onset, depending on the strength and toughness of the material, the amount of energy can be sufficiently large to give rise to a more or less dense lattice of cracks. Following, after initiation, when the crack tips are close to the support, the newly created small cells tend to separate from it, thicker the film and more harmful the debonding.

Abstract: Fine nanoporous copper was fabricated from the amorphous Ti-Cu alloys with a minor addition of silver in 10 mM HF solutions. The pore sizes decreased from 100 nm to 12 nm with the increase of the Ag contents in comparison of Ti₆₀Cu₄₀ ribbons free of Ag. With increasing of the dealloying time, the sizes of the nanopores and ligaments increased for the nanostrucutres on Ti₆₀Cu₃₈Ag₂ ribbons since the segregation of the Ag phase which triggered the galvanic dissolution of the adjacent Cu matrix in form of micro-couplings to further coarsen the nanoporous Cu. On the contrary, the trace formation of the Ag phase on the Ti₆₀Cu₃₉Ag₁ ribbons had a weak ability to motivate the galvanic dissolution, indicating by the constant pore sizes and slight decrease in the ligament sizes with the increase in the dealloying time. The refinement of the nanoporous structures was ascribed to the drastic decrease in the surface diffusivity. The decrease in the surface diffusivity due to the involvement of Ag with a lower surface diffusivity in comparison of Cu was more than one order of magnitude. The involvement of Ag adatoms restricted the diffusion of Cu adatoms in the interface regions in the inward and outward directions.

Abstract: The author introduces and summarizes the results on bottom-up formation and structural characterizations obtained so far for the MnAs nanoclusters and MnAs/semiconductor nanowire hybrids. First, MnAs nanoclusters were grown by selective-area metal-organic vapor phase epitaxy. They had a hexagonal NiAs-type crystal structure. Their <00(0)1> direction was parallel to <111>B direction of zinc-blende-type GaAs substrates. Hybrid MnAs/GaAs nanowires, subsequently, were fabricated by combining selective-area metal-organic vapor phase epitaxy of GaAs nanowire templates and endotaxial MnAs nanoclustering on them. MnAs nanoclusters ordered at six ridges of hexagonal GaAs nanowires were formed possibly owing to more atomic steps between {0-11} crystal facets. In the case of hybrid MnA/InAs nanowires, MnAs nanoclusters were not formed only on the {0-11} side-walls, and/or ridges between them, but on the top {111}B crystal facets of hexagonal InAs nanowires. MnAs nanoclusters were formed much deeper into the InAs nanowires than into the GaAs nanowires. These facts are possibly due to the InAs nanowires are thermally less stable than the GaAs nanowires. Some of the hybrid MnA/InAs nanowires were bent at the parts where the MnAs nanoclusters were grown into the host nanowires mainly owing to the strain effects.

Abstract: A periodic structure of gold nanoparticles (AuNPs) is formed by reducing a solution of gold chloride using novel plasma techniques, where a spatio-periodically generated plasma is transcribed to the AuNP structure formed on the ionic liquid (IL) surface under the strong magnetic field. In addition, it is found that a ring-shaped AuNP structure is formed corresponding to the shape of a ring electrode inserted into the plasma, where the AuNPs are synthesized at the position without plasma irradiation due to the shielding by the ring electrode. On the other hand, the periodic structure of the AuNPs are synthesized on the carbon nanotubes (CNTs) working as a template, where the controlled ion irradiation to the IL including functional groups can realize the distance-controlled synthesis of the AuNPs by dissociation of the IL and the functionalization of the CNTs by the dissociated carboxyl and amino groups. Furthermore, DNA is used as the functional group which connects the AuNPs to the CNTs. The mono-dispersed and high-density AuNPs are synthesized on the CNTs in the same way as the carboxyl and amino groups.

Abstract: Silicon nanocrystals (SiNCs) have unique optical and electronic properties that are advantageous for semiconductor device applications and here their application to solar cell is presented. Free-standing, narrow size distribution SiNCs were synthesized by non-thermal plasma using silicon tetrachloride (SiCl4) successfully. Blended solution of as-produced SiNCs and P3HT, or Poly(3-hexylthiophene-2,5-diyl), was spin-casted to form bulk heterojunction solar cell devices. As the weight fraction of SiNCs increased up to 50 wt%, the short circuit current and the power conversion efficiency dramatically increased, while the open circuit voltage and the fill factor do not change significantly. The improved performance is attributable to increased probability of exciton dissociation at acceptor SiNCs and donor P3HT interface.

Abstract: In this work, W, P and faujasite zeolites were synthesized using fly ash as raw material, a waste material derived of coal fired plants in Mexico. Two different synthesis methods were used. Zeolites were submitted a functionalization treatment exchanging their metallic ions by ammonium, aluminum and ferrous ions. Chemical, structural and textural properties of functionalized zeolites were evaluated. As (V) and As (III) adsorption capacity of modified zeolites were assessed. Changes on their structural properties were no significant. While the textural properties such as pore volume, specific surface area and pore size distribution were dependent of nature of ion exchanged, and the accessibility of extra-framework sites of the zeolites. Functionalization with di and trivalent ions allow changing the zeolitic surface charge. This modification led to increase their ability to adsorb anionic species from aqueous solutions. The results shown that, the adsorption capacity was dependent of zeolite type and their chemical surface nature. W zeolite modified with aluminum ions achieved the highest arsenic (V) adsorption capacity. While ferrous functionalization on W zeolite shown a high affinity to remove As (III) species from aqueous solutions.

Abstract: The present study aims at evaluating the gas bubbling method, based on the use of dry air as a gaseous phase, for the production of Al based metal matrix nanocomposites through a proper gas-liquid reaction. In particular, Al₂O₃ reinforcement particles were in-situ synthesized in molten commercially pure Al through a gas bubbling oxidation technique. Dry air was injected in the melt in order to induce a controlled oxidation of the molten matrix. SEM-EDS analysis on the produced samples revealed the presence of alumina particles, ranging from the nanoto the micrometric size, demonstrating the feasibility of the process. A hardness increase on the produced samples confirmed the strengthening effect of the in-situ produced ceramic particles.