Thermal Plasma Processing of Nanostructured Si-based Ceramic Materials

A novel thermal plasma process, based on Thermal Plasma Chemical Vapor Deposition (TPCVD) for producing nanostructured ceramics from liquid precursors is described. The process combines the rapid thermal decomposition of low-cost liquid precursors injected into an Inductively Coupled Plasma (ICP) with a fast gas phase condensation due to the high cooling rate and short residence time existing in such a plasma. Examples of synthesis of Si-based nanostructured ceramic materials (SiC, Si₃N₄) as powders or coatings are given. Deposition rates of up to 10 m/min can be achieved by the present technique.     

Specific features of luminescence properties of nanostructured aluminum oxide

Aluminum oxide nanopowders are prepared by the gas phase method and characterized according to the particle sizes and the phase composition. Samples of the nanostructured ceramic material are produced by pressing and annealing in air. The photoluminescence and cathodoluminescence spectra of the Al₂O₃ nanostructured ceramic material and α-Al₂O₃ anion-defect single crystals are investigated under comparable conditions. The luminescence bands of centers formed by oxygen vacancies are revealed in the spectra of two types of samples. The nanostructured ceramic material is characterized by the appearance of a new luminescence band at 3.4 eV and a decrease in the luminescence decay time. The inference is made that the characteristic features of the luminescence of the nanostructured ceramic material can be associated with the presence of non-equilibrium phases and the specific features of relaxation processes.     

Dry Powder Precursors of Cubic Liquid Crystalline Nanoparticles (cubosomes)

Cubosomes are dispersed nanostructured particles of cubic phase liquid crystal that have stimulated significant research interest because of their potential for application in controlled-release and drug delivery. Despite the interest, cubosomes can be difficult to fabricate and stabilize with current methods. Most of the current work is limited to liquid phase processes involving high shear dispersion of bulk cubic liquid crystalline material into sub-micron particles, limiting application flexibility. In this work, two types of dry powder cubosome precursors are produced by spray-drying: (1) starch-encapsulated monoolein is produced by spray-drying a dispersion of cubic liquid crystalline particles in an aqueous starch solution and (2) dextran-encapsulated monoolein is produced by spray-drying an emulsion formed by the ethanol–dextran–monoolein–water system. The encapsulants are used to decrease powder cohesion during drying and to act as a soluble colloidal stabilizer upon hydration of the powders. Both powders are shown to form (on average) 0.6m colloidally-stable cubosomes upon addition to water. However, the starch powders have a broader particle size distribution than the dextran powders because of the relative ease of spraying emulsions versus dispersions. The developed processes enable the production of nanostructured cubosomes by end-users rather than just specialized researchers and allow tailoring of the surface state of the cubosomes for broader application.     

Nanostructured core-shell Ni deposition on SiC particles by alkaline electroless coating

In this study, core-shell nanostructured nickel formation on silicon carbide (SiC) ceramic powders was achieved through the electroless deposition method using alkaline solutions. To produce a nano core-shell Ni deposition on the SiC surfaces, process parameters such as pH values, the type of reducer material, deposition temperature, stirring rate and activation procedure among others were determined. Full coverage of core-shell nickel structures on SiC surfaces was achieved with a grain size of between 100 and 300 nm, which was approximately the same deposition thickness on the SiC surfaces. The surface morphology of the coated SiC particles showed a homogenous distribution of nanostructured nickel grains characterized by scanning electron microscopy and X-ray diffraction techniques. The nanostructures of the crystalline Ni coatings were observed to be attractive for achieving both good bonding and dense structure. The thin core shell-structure of Ni on the SiC surfaces was assessed as a beneficial reinforcement for possible metal matrix composite manufacturing.     

Particle surface treatment for nanocomposites containing ceramic particles

Polymer matrix composites containing dispersed ceramic nanoparticles were formed by UV activated photopolymerization from the reactive liquid monomer hexanediol-diacrylate (HDODA). The polymer forming reaction proceeds by a free-radical mechanism. In forming polymer composites that contain nanoparticles, dispersing the particles as discrete entities is critical for developing optimum properties. In the as-received condition, ceramic particles are aggregated. They must be dispersed in the monomer but if the particles are not surface treated and stabilized, they rapidly settle out of the suspension. Surface modification of the ceramic allows the particles to be suspended in the organic monomer and stabilizes the dispersion so that the particles will not reagglomerate. In this study silanes were employed as surface modifiers to disperse two nano-particulate ceramics in the HDODA monomer. The ceramic particles used are silicon carbide (SiC) and barium titanate (BaTiO₃). The shapes and sizes of the ceramic particles were established using transmission electron microscopy (TEM). A method for dispersing nanoparticles was developed in which silane-treated particles were stabilized so that they did not settle out of the liquid monomer. An analytical method based on atomic force microscopy (AFM) was used to characterize the particle distribution in the cured composites. Focusing on work with SiC nanoparticles in HDODA as a model system, the process for silane application was advanced so that it successfully yielded composites having no aggregates with particle sizes closely matching those of the neat ceramic particles.     

Fast interfacial ionic conduction in nanostructured glass ceramics

The hopping movements of mobile ions in a nanostructured LiAlSiO4 glass ceramic are characterized by time-domain electrostatic force spectroscopy (TDEFS). While the macroscopic conductivity spectra are governed by a single activation energy, the nanoscopic TDEFS measurements reveal three different dynamic processes with distinct activation energies. Apart from the ion transport processes in the glassy and crystalline phases, we identify a third process with a very low activation energy, which is assigned to ionic movements at the interfaces between the crystallites and glassy phase. Such interfacial processes are believed to play a key role for obtaining high ionic conductivities in nanostructured solid electrolytes.     

Nanoscale surface of carbon nanotube fibers for medical applications: Structure and chemistry revealed by TOF-SIMS analysis

Surface structure and related chemistry understanding is a vital element in the design of high biocompatible materials since adsorption and adhesion of biological components are involved. These features are even more important in the case of nanostructured materials such as carbon nanotubes (CNTs) fibers. In our preliminary work we synthesised CNTs based fibers for medical applications. This new hybrid system combines polyvinyl alcohol (PVA) with CNTs and polylactic-co-glycolic acid (PLGA), a biodegradable copolymer. The surface properties of this material are investigated in order to guarantee a biocompatible response. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was found to be an ideal tool for fiber characterisation owing to its capacity to provide chemical specificity combined with detection limits beyond the reach of techniques previously used. Complementary morphological information is provided by atomic force microscopy (AFM). The corroboration of both data enables us to define the chemistry and structure of this new formulation.     

Synthesis of carbon nanotubes directly over TEM grids aiming the study of nucleation and growth mechanisms

A novel approach to produce electron-transparent multi-layer membranes over TEM grids for transmission electron microscopy analysis is presented. The membranes have been used to grow and analyze carbon nanostructured materials in a thermal-chemical vapor deposition process using Ni and Cu as catalysts and silicon oxide thin films as support layers, at temperatures as high as 900 °C. It is important that conditions of the synthesis using the electron-transparent multi-layer membrane system are similar to those for a conventional chemical vapor deposition process, where oxidized silicon wafers are employed. In particular, the thickness of the silicon oxide and the catalyst layers are the same, and similar carbon tubular structures were grown using both substrates. The use of membranes was crucial especially for the study of the nucleation mechanism for carbon nanotubes. These electron-transparent multi-layer membranes are relatively easy to obtain and they can be used for transmission electron microscopy studies of high-temperature synthesis of different nanostructured materials.     

Morphology of Tungsten Nanooxides,Synthesized by Laser Ablation of Metal in Water

Colloidal solution precipitates obtained during laser ablation of tungsten in water and containing nanostructured metal oxides are studied using X-ray diffraction and scanning electron microscopy. The nanostructure composition and morphology are analyzed. It is shown that the material composing nanostructures is X-ray amorphous, i.e., the particle size does not exceed 1–2 nm. The high degree of the structure surface development implies prospects of their use as substrata when analyzing the composition of various materials by surface-enhanced Raman scattering.     

Advanced industrial ceramic heat pipe recuperators

This paper summarizes the results of an investigation involving the use of ceramic heat pipe recuperators for high-temperature heat recovery from industrial furnaces. The function of the recuperator is to preheat combustion air with furnace exhaust gas. To maximize fuel savings, a very high air preheat temperature is desirable; this necessitates the use of ceramic elements in the recuperator.The heat pipe recuperator comprises a bundle of individual ceramic heat pipes acting in concert, with a partition separating the air and exhaust gas flow streams. The heat pipe fluid is a liquid metal. The ceramic heat pipe recuperator concept offers several advantages as compared to tubular type ceramic recuperators. Because each heat pipe is essentially an independent heat exchanger, the failure of a single tube does not compromise recuperator integrity and has only a minimal effect on overall heat exchanger performance. This independent element characteristic also enables easier replacement of individual heat pipes in the recuperator. In addition, the heat pipe acts as an essentially isothermal heat transfer device, leading to a high thermodynamic efficiency.Cost estimates developed for heat pipe recuperator systems indicate favorable payback periods. Laboratory studies have demonstrated the feasibility of fabricating the required ceramic tubes, coating the inside of the tubes with CVD tungsten (which functions as both a protective layer and a heat pipe fluid wick), and sealing the heat pipe with an electron-beam-welded or vacuum-brazed end cap.     

Characterization of cold-sprayed nanostructured Fe-based alloy

The ball-milled Fe-Si alloy was used as feedstock for deposition of nanocrystalline Fe-Si by cold spraying process. The microstructure of the as-sprayed nanostructured Fe-Si was characterized by using optical microscopy, scanning electron microscopy and transmission electron microscopy. The grain sizes of the feedstock and as-sprayed deposit were estimated based on X-ray diffraction analysis. The microhardness and coercivity of the deposited Fe-Si alloy were characterized. The results showed that the as-sprayed deposit presented a dense microstructure. The mean grain size of the as-deposited Fe-Si was several tens nanometers and comparable to that of the corresponding milled feedstock. The temperature of driving gas presented little effect on the microstructure of cold-sprayed nanostructured Fe-Si deposit. The mechanical alloying induced oxygen contents up to 8 wt% in the feedstocks and subsequent deposits. The microhardness of the deposit reached about 400 Hv. The deposit achieved a high coercivity up to 190 kA/m indicating the potential possibility for applications to recording materials.     

Template-free synthesis of hierarchical NiO microtubes as high performance anode materials for Li-ion batteries

Hierarchical nanostructured NiO (h-NiO) microtubes were prepared by a simple wet-chemical synthesis without the use of template or surfactant, followed by the calcination of α-Ni(OH)₂ precursor. The structural characterization of the h-NiO microtubes were performed by scanning microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD), the results of which indicated that the obtained h-NiO microtubes are covered by the nanosheet grown perpendicularly on the tube surface. The unique hierarchical nanostructure of h-NiO microtubes with high surface area and many voids facilitates the electrochemical reaction as well as the short ion and electron transport pathway. Therefore, as anode electrode of Li-ion batteries, the h-NiO microtubes deliver largely enhanced cycle capacity of 770 mAh·g⁻¹ at a current density of 0.5 C after 200 cycles with high columbic efficiency, compared to the NiO rods. These results suggest that the h-NiO microtubes can be a promising anode material for Li-ion batteries.     

Picosecond and femtosecond pulsed laser ablation and deposition of quasicrystals

A Nd:glass laser with pulse duration of 250 fs and 1.3 ps has been used to evaporate a Al₆₅Cu₂₃Fe₁₂ quasicrystalline target. The gaseous phase obtained from the ablation process has been characterised by several techniques such as emission spectroscopy, quadrupole mass spectrometry and ICCD imaging, used to study the plume composition, energy and morphology. The results show that the ablation processes in the short-pulse regimes are very different to the nanosecond one. In particular the plume angular distribution shows a characteristic high cosine exponent and the composition is completely stoichiometric and independent from the laser fluence. Furthermore the mass spectra indicate the presence of clusters, both neutral and ionised and the emission from the target suggest a rapid thermalisation leading to the melting of the surface. To clarify the ablation process some films have been deposited, on oriented silicon, at different experimental conditions and analysed by scanning electron microscopy, atomic force microscopy, energy dispersive X-ray analysis and X-ray diffraction. The analyses show the presence of nanostructured films retaining the target stoichiometry but consisting of different crystalline and non crystalline phases. In particular the nanostructure supports the hypothesis of the melting of the target during the ablation and a mechanism of material ejection is proposed for both picosecond and femtosecond regimes.     

Urea-assisted solvothermal synthesis of monodisperse multiporous hierarchical micro/nanostructured ZnCo<Subscript>2</Subscript>O<Subscript>4</Subscript> microspheres and their lithium storage properties

High-quality monodisperse multiporous hierarchical micro/nanostructured ZnCo₂O₄ microspheres have been fabricated by calcinating the Zn_1/3Co_2/3CO₃ precursor prepared by urea-assisted solvothermal method. The as-prepared products are characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), and Brunauer-Emmett-Teller (BET) measurement to study the crystal phase and morphology. When tested as anode material for lithium ion batteries, the multiporous ZnCo₂O₄ microspheres exhibit an initial discharge capacity of 1,369 mAh g^?1 (3,244.5 F cm^?3) and retain stable capacity of 800 mAh g^?1 (1,896 F cm^?3) after 30 cycles. It should be noted that the good electrochemical performances can be attributed to the porous structure composed of interconnected nanoscale particles, which can promote electrolyte diffusion and reduce volume change during discharge/charge processes. More importantly, this ZnCo₂O₄ 3D hierarchical structures provide a large number of active surface position for Li⁺ diffusion, which may contribute to the improved electrochemical performance towards lithium storage.     

Synthesis and characterization of nanostructured bimetallic films on α-Al2O3 substrates using electroless deposition

The Pt-Pd and Pd-Ag nanostructured bimetallic films on porous α-Al₂O₃ substrates are successfully synthesized by chemical deposition using lyotropic liquid crystalline templating strategy. The co-reduction of two metallic species in the presence of liquid crystalline phase by hydrazine hydrate produces hexagonal nanostructured Pt-Pd and lamellar nanostructured Pd-Ag films. Low-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies show the ordered nanostructure of both Pt-Pd and Pd-Ag films. The energy dispersive X-ray (EDX) and wide-angle XRD analyses of the bimetallic films have verified the coexistence and uniform distribution of constituent metallic species. By taking into account of catalytic activities, well-defined nanochannels and higher surface areas, the nanostructured bimetallic films might have application potential in microreactors.     

Electron relaxation and transport in nanostructured and bulk silica

Processes of ballistic and hot electron relaxation in extended bulk as well as nanostructured silica have been analyzed by means of a phonon-based scattering model and respective Monte-Carlo computer simulation. Optical as well as acoustic phonons are taken into account. Trajectories of electrons and their energy attenuation in nanostructured silica are additionally affected by scattering processes at the grain boundaries between the nanoparticles, i.e. by surface phonon as well as potential scattering. Moreover, a flatter conduction band and a higher effective electron mass have been taken into account too. According to these calculations, electrons with an initial energy of several eV, but still below the valence band ionization threshold, were thermalized in 50–300 fs increasing with the silica grain size from 1 nm up to bulk material. The electron emission probabilities over the surface barrier into vacuum are extended up to depths of 60–100 nm, respectively, increasing with enhancement by an electric field.     

Applications of the electron backscatter diffraction technique to ceramic materials

A technique with a relatively high spatial resolution is required for an effective analysis of the microstructure of ceramic materials. The recently developed electron backscatter diffraction (EBSD) technique, which works within a scanning electron microscope, enables a spatially highly resolved study of crystallographic orientations while recording Kikuchi patterns on a user-defined grid. However, such an EBSD texture analysis was until now not often performed on ceramic materials – in contrary, the technique is widely employed in the analysis of metallic materials, including the investigation of various types of steels. The use of ceramics possesses a variety of problems for EBSD investigations like: (i) complicated crystal structure, (ii) difficult surface preparation, and (iii) problems arising from a low conductivity of the ceramic materials. Here, we discuss these problems and present solutions in order to obtain high-quality Kikuchi patterns from such ceramics.     

A siloxane polymer lightwave circuit on ceramic substrate applicable to ultrafast optoelectronic multi-chip-modules

Technique for integrating optical waveguide circuits on electrical circuits is developed toward the application to opto-electronic multi-chip modules (O/E-MCM), which enables one to handle ultrafast lightwave pulses and electrical signals on a common circuit board. We use ceramic material as the substrate of O/E-MCM having a multi-layer structure. A siloxane polymer is utilized to form low loss optical waveguides on ceramic substrates by low temperature processes. The waveguide has shown high transparency around 1310 nm. The group velocity dispersion has been measured and shown to become almost zero at wavelength of 1310 nm and about 0.4 fs/cm nm at 1550 nm. An optical circuit has been formed on simple electrical circuit consisting of a thermometer film resistance layer. A Mach–Zehnder interferometer optical switch exhibiting the waveguide extinction ratio of 30 dB, control power of 5 mW, and switching speed of 6 ms has been demonstrated. Thermal management characteristics also have been demonstrated successfully. This single-mode optical waveguide can thus be formed readily on ceramic substrates involving electrical circuit layers; this result confirms its applicability to O/E-MCM.     

Scaling laws for the spatial distributions of the plasma parameters in the positive column of a dc oxygen discharge

Comprehensive self-consistent simulations of the positive column plasma of a dc oxygen discharge are performed with the help of commercial CFDRC software (), which enables one to carry out computations in an arbitrary 3D geometry using fluid equations for heavy components and a kinetic equation for electrons. The main scaling laws for the spatial distributions of charged particles are determined. These scaling laws are found to be quite different in the parameter ranges that are dominated by different physical processes. At low pressures, both the electrons and negative ions in the inner discharge region obey a Boltzmann distribution; as a result, a flat profile of the electron density and a parabolic profile of the ion density are established there. In the ion balance, transport processes prevail, so that ion heating in an electric field dramatically affects the spatial distribution of the charged particles. At elevated pressures, the volume processes prevail in the balance of negative ions and the profiles of the charged particle densities in the inner region turn out to be similar to each other.     

加速器-电子显微镜联机进行材料科学研究的新进展

离子或电子辐照引起的材料微结构演变是一个非常复杂的过程.用加速器 电子显微镜联机装置可原位观察载能离子束辐照及辐照后退火引起的材料微结构演变,并确定相应的辐照条件.介绍了近10年来国际上利用加速器 电子显微镜联机装置开展材料科学研究的最新进展.Ion beam or electron beam irradiation will lead to the change of material microstructure. By the use of facilities composed of an electron microscope and ion accelerator(s), the microstructure evolvement in material can be in situ studied during the irradiation and following annealing processes. The facilities have been widely used to study many kinds of materials, e.g. metal, alloy, ceramic materials and semiconductor, in the past twenty years. In this paper the development of the Accelerator and Electron ...