Synthesis Of Nanocrystalline Materials Research Articles

The effect of inclination angle on the plastic deformation behavior of bicrystalline silver nanowires with Σ3 asymmetric tilt grain boundaries

Atomistic simulations were used to investigate the plastic deformation behavior of bicrystalline silver nanowires with Σ3 asymmetric tilt grain boundaries at 0.1K. The calculated grain boundary energies of Σ3 asymmetric tilt grain boundaries corresponded well with the energies measured in experiments and predicted by the theoretical description. The Σ3 asymmetric tilt grain boundaries with low inclination angles were composed of a replication of twin boundary segments separated by small ledges. The results demonstrated that the combination effect of Schmid factor and non-Schmid factors could explain dislocations emission into grain 1 only in models with low inclination angles (Ф<64.76°). At the latter stage of plastic deformation, free surfaces served as additional dislocation sources. Parallelly arranged operative slip systems were the fundamental features of plastic deformation. In addition, a number of stacking faults and multiple stacking faults were formed during plastic deformation. The hindrance of stacking faults to dislocation motion and the interactions between dislocations leaded to the observed strain hardening in nanowires with inclination angles at and above 29.50°. The low stacking fault energy of silver was responsible for the appearance of strain hardening. Dislocations emitted from grain 2 interacted with each other contributing to the observed strain hardening. Grain boundaries were completely eliminated by successive emission of dislocations from grain boundaries in nanowires with an inclination angle of 35.26° and 54.74°. A detailed understanding of the relationship between strength and grain boundary structures as well as specific plastic deformation would push forward the application of nanocrystalline materials and provide insights into the synthesis of nanocrystalline materials with superior strength and ductility.

Phase decomposition and nano structure evolution of metastable nanocrystalline Cu-Co solid solutions during thermal treatment

Nanocrystalline and ultrafine-grained Cu100-xCox (x = 26 and 76) solid solutions have been prepared by severe plastic deformation (SPD) of elemental powder mixtures. For both concentrations a supersaturated solid solution fcc phase was identified after the deformation process with grain sizes of less than 50 nm for Co rich solutions and around 100 nm for Cu rich solutions. Additionally, synthesis of nanocrystalline materials in the Cu-Co alloy system by electrodeposition has been conducted. Microstructural characterization by scanning and transmission electron microscopy, differential scanning calorimetry, and microhardness measurements are used to investigate the structural evolution, the thermal stability and mechanical properties of the different nanocrystalline Cu-Co alloy materials during isothermal and non-isothermal annealing. In this study it is shown that the phase decomposition of the metastable Cu-Co solid solutions has a significant influence on their thermal stability, which can be linked to the underlying microstructure that forms during annealing.

Synthesis of Nano-Crystalline Materials in Open-Air Laboratory: A Case Study of Tobacco.

The work deals with synthesis of nano-crystalline materials in open-air laboratory and in-depth investigation of the tobacco sample of one branded cigarette and its ash using high-resolution transmission electron microscopy and associated techniques. It exhibits the presence of nanocrystals and nanorods of various oxides in cigarette ash. The structure, shape, size and composition of these nanocrystals and nanorods are explored. The energy dispersive X-ray spectra from different regions of the tobacco sample and its ash using high-angle annular dark field scanning/transmission electron microscopy mode are utilized to obtain elemental composition and their relative abundances. For a detailed distribution of different elements in the nanorods, elemental mapping using energy-filtered transmission electron microscopy is also presented. The results highlight the conversion of amorphous constituents of tobacco to nanomaterials on combustion at low temperatures, thus mixing up in the atmosphere.

Synthesis of nanocrystalline materials through reverse micelles: A versatile methodology for synthesis of complex metal oxides

We have been successful in obtaining monophasic nanosized oxides with varying chemical compositions using the reverse micellar method. Here we describe our methodology to obtain important metal oxides like ceria, zirconia and zinc oxide. The oxalate of cerium, zirconium and zinc were synthesized using the reverse micellar route. While nanorods of zinc oxalate with dimension, 120 nm in diameter and 600 nm in length, could be obtained, whereas spherical particles of size, 4–6 nm, were obtained for cerium oxalate. These precursors were heated to form their respective oxides. Mixture of nanorods and nanoparticles of cerium oxide was obtained. ZrO2 nanoparticles of 3–4 nm size were obtained by the thermal decomposition of zirconium oxalate precursor. ZnO nanoparticles (55 nm) were obtained by the decomposition of zinc oxalate nanorods. Photoluminescence (PL) studies at 20 K shows the presence of three peaks corresponding to free excitonic emission, free to bound and donor-acceptor transitions. We also synthesized nanoparticles corresponding to Ba1−x Pb x ZrO3 using the reverse micellar route. The dielectric constant and loss were stable with frequency and temperature for the solid solution.

Thermogravimetry-evolved gas analysis-mass spectrometry system for materials research

Thermal analysis is a widely used analytical technique for materials research. However, thermal analysis with simultaneous evolved gas analysis describes the thermal event more precisely and completely. Among various gas analytical techniques, mass spectrometry has many advantages. Hence, an ultra high vacuum (UHV) compatible mass spectrometry based evolved gas analysis (EGA-MS) system has been developed. This system consists of a measurement chamber housing a mass spectrometer, spinning rotor gauge and vacuum gauges coupled to a high vacuum, high temperature reaction chamber. A commercial thermogravimetric analyser (TGA: TG + DTA) is interfaced to it. Additional mass flow based gas/vapour delivery system and calibration gas inlets have been added to make it a versatile TGA-EGA-MS facility. This system which gives complete information on weight change, heat change, nature and content of evolved gases is being used for (i) temperature programmed decomposition (TPD), (ii) synthesis of nanocrystalline materials, (iii) gas-solid interactions and (iv) analysis of gas mixtures. The TPD of various inorganic oxyanion solids are studied and reaction intermediates/products are analysed off-line. The dynamic operating conditions are found to yield nanocrystalline products in many cases. This paper essentially describes design features involved in coupling the existing EGA-MS system to TGA, associated fluid handling systems, the system calibration procedures and results on temperature programmed decomposition. In addition, synthesis of a few nanocrystalline oxides by vacuum thermal decomposition, gas analysis and potential use of this facility as controlled atmosphere exposure facility for studying gas-solid interactions are also described.

Synthesis of nanocrystalline material by sputtering and laser ablation at low temperatures

Physical vapor deposition techniques such as sputtering and laser ablation – which are very commonly used in thin film technology – appear to hold much promise for the synthesis of nanocrystalline thin films as well as loosely aggregated nanoparticles. We present a systematic study of the process parameters that facilitate the growth of nanocrystalline metals and oxides. The systems studied include TiO2, ZnO, γ-Al2O3, Cu2O, Ag and Cu. The mean particle size and crystallographic orientation are influenced mainly by the sputtering power, the substrate temperature and the nature, pressure and flow rate of the sputtering gas. In general, nanocrystalline thin films were formed at or close to 300 K, while loosely adhering nanoparticles were deposited at lower temperatures.

MATERIAL PROCESSING VIA AN INTEGRATED MECHANICAL AND THERMAL ACTIVATION PROCESS

This paper reviews the recent progress in material synthesis and processing based on mechanical activation approaches. Material processing based on mechanical alloying and attrition has been widely used to prepare metastable phases, amorphous alloys, composites, and nanostructured materials. The most recent progress made in mechanical activation is the development of a new process that integrates mechanical activation and thermal activation to produce novel materials as well as conventional materials. The integrated mechanical and thermal activation (IMTA) process represents one of the most exciting recent advancements and holds great promise for commercial viability. Examples of enhanced reaction rates and synthesis of nanocrystalline materials are provided to illustrate the progress brought about by the IMTA process.

Synthesis of nanocrystalline materials — an overview

This paper reviews research work at the Institute for Materials and Advanced Processes (IMAP), University of Idaho, on the synthesis of nanocrystalline materials and their consolidation. Nanocrystalline materials have been synthesized by a number of ‘far from equilibrium processes’, including mechanical alloying (MA), mechanochemical processing (MCP), supercritical fluid processing (SCFP), and severe plastic deformation (SPD). Examples of the materials include the Ti–Al based intermetallic compounds and composites produced by MA and SPD, Ti base alloys and metal carbides synthesized by MCP, thin film Cu produced by SCFP, and Al–Fe alloys produced by SPD. Details of the processes used and the enhancement of properties due to the nanoscale structures in consolidated material will be presented. The potential of these processes to substitute for conventional methods of production will also be discussed.

Tensile Superplasticity in Nanomaterials - Some Observations and Reflections

The synthesis of nanocrystalline materials has provided new opportunities to explore grain size dependent phenomenon to a much finer scale. Superplasticity is a well-established grain size dependent phenomenon. In this paper, we analyze some of the tensile superplasticity data obtained in the last few years on Ti-6Al-4V, Ni 3 Al, and 1420-Al alloy processed by severe plastic deformation (SePD). The experimental results show higher flow stresses for superplasticity in nanocrystalline materials than in microcrystalline materials. It is suggested that the conventional slip accommodated grain boundary sliding is likely to be difficult in nanomaterials.

Synthesis of Nanocrystalline Materials from Amorphous Solids

The key to the formation of nanocrystallites from amorphous solids lies in the annealing temperature. This aspect of the preparation of nanocrystalline materials is covered, as are other attractive features of this method, for example, that it can be applied to most alloy and pure element systems, large quantities of nanocrystalline samples can be produced, and the grain size can be controlled. The properties of these materials are also described and it is concluded that more studies on 3D bulk: porosity-free, and clean samples are needed.

High temperature deformation behavior of a nanocrystalline titanium aluminide

Gamma titanium intermetallic alloys are potentially attractive for elevated temperature applications. The room temperature ductility and fracture toughness have been improved considerably by the addition of ternary and quaternary elements. The synthesis of nanocrystalline materials has provided further avenues for possible improvement in the mechanical properties. The exciting prospect of low temperature superplasticity in nanocrystalline materials has been discussed. Recently, nanocrystalline {gamma}-TiAl alloys have been synthesized by hot isostatic pressing (HIP) of mechanically alloyed (MA) Ti-47.5 Al-3 Cr (at.%) powders. The purpose of this study was to evaluate the possibility of observing low temperature superplasticity in this nanocrystalline alloy. By determining the stress exponent for flow, it should be possible to comment on the micromechanism of deformation in a nanocrystalline intermetallic alloy. A number of studies have shown that superplasticity is possible in {gamma}-TiAl alloys and it is important to establish whether the scaling law extends to nanocrystalline {gamma}-TiAl regime or the flow behavior changes.

Synthesis of nanocrystalline NbAl3 by laser ablation technique

Synthesis of nanocrystalline material has been developed using laser ablation technique. NbAl3 nanocrystalline powders have been synthesized by laser ablation and identified by transmission electron microscopy (TEM). The average particle size was measured about 5.0 nm. Production yield and ablation rate were obtained as a function of He background pressure and laser pulse energy by measuring the weight of produced powders and weight loss of the target material before and after experiment. The ablation rate appeared to be relatively constant over the range of the He gas pressure. Production rate varied along with both He gas pressure and laser pulse energy. Optimum condition for efficiently high production rate is at 1.0 Torr of He gas pressure and at 320 mJ of the laser pulse energy.

High pressure magnetron sputter gun

A commercial planar magnetron sputter gun was modified for operation in argon or oxygen at pressure up to 2 Torr. This high pressure gun may be useful for uniform deposition of high Tc superconductor thin films and synthesis of nanocrystalline materials.