In situ synthesis of silica gel nanowire/Na+-montmorillonite nanocomposites by the sol-gel route

Silica-gel nanowire/Na+-montmorillonite (Na+-MMT) nanocomposites were prepared by the in situ sol-gel process of tetraethyl orthosilicate (TEOS) in the presence of Na+-MMT and ammonia as catalyst. Microstructure characterization of the nanocomposites was done by SEM, , EDX, XRD and FTIR. It was found that a lot of silica-gel nanowires grew along the edges of Na+-MMT. The combination between the nanowires and Na+-MMT was accomplished via polycondensation of the hydrolyzed TEOS and the edge-OH groups of Na+-MMT.

Formation of epsilon-FeXN/BN magnetic nanocomposite and its thermodynamic and kinetic analyses

A nanocomposite of nanometer-sized magnetic granular epsilon-FeXN embedded in a nonmagnetic amorphous boron nitride matrix was prepared by ball milling mixture of alpha-Fe and hexagonal boron nitride in argon atmosphere. The grain size of the epsilon-FeXN alloy was about 10-20 nm. The nitrogen concentration in the epsilon-FeXN alloy increases with extending milling time. Both thermodynamic calculation and the present experiment show that iron and nitrogen atoms have higher alloying driving force than iron and boron atoms. Analyses of thermodynamics and kinetics about formation of the epsilon-FeXN alloy suggested that the formation of the epsilon-FeXN alloy is related to amorphization of the hexagonal boron nitride and refinement of the alpha-Fe. II was found from the present experiment that a critical grain size of the alpha-Fe reacting with nitrogen in the amorphous boron nitride is about 8 nm.

Synchrotron-laser pump-probe luminescence spectroscopy: Correlation of electronic defect states with x-ray absorption in wide-gap solids

Poolton, Nigel; Hamilton, B.; Evans, D.A., (2005) 'Synchrotron-laser pump-probe luminescence spectroscopy: Correlation of electronic defect states with x-ray absorption in wide-gap solids', Journal of Physics D: Applied Physics 38 pp.1478-1484 RAE2008

Observation of K-Shell Soft X Ray Emission of Nitrogen Irradiated by XUV-Free Electron Laser FLASH at Intensities Greater than 10(16) W/cm(2)

In the past few years, the development of light sources of the 4(th) generation, namely XUV/X-ray Free Electron Lasers provides to the scientific community outstanding tools to investigate matter under extreme conditions never obtained in laboratories so far. As theory is at its infancy, the analysis of matter via the self-emission of the target is of central importance. The characterization of such dense matter is possible if photons can escape the medium. As the absorption of K-shell X-ray transitions is minimal, it plays a key role in this study. We report here the first successful observation of K-shell emission of Nitrogen at 430 eV using an XUV-Free Electron Laser to irradiate solid Boron Nitride targets under exceptional conditions: photon energy of 92 eV, pulse duration of similar to 20 fs, micro focusing leading to intensities larger than 10(16) W/cm(2). Using a Bragg crystal of THM coupled to a CCD, we resolved K-shell line emission from different charge states. We demonstrate that the spectroscopic data allow characterization of electron heating processes when X-ray radiation is interacting with solid matter. As energy transport is non-trivial because the light source is monochromatic, these results have an important impact on the theory. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Wear of coated and uncoated PCBN cutting tool used in turning and milling

This licentiate thesis has the main focus on evaluation of the wear of coated and uncoated polycrystalline cubic boron nitride cutting tool used in cutting operations against hardened steel. And to exam the surface finish and integrity of the work material used. Harder work material, higher cutting speed and cost reductions result in the development of harder and more wear resistance cutting tools. Although PCBN cutting tools have been used in over 30 years, little work have been done on PVD coated PCBN cutting tools. Therefore hard turning and hard milling experiments with PVD coated and uncoated cutting tools have been performed and evaluated. The coatings used in the present study are TiSiN and TiAlN. The wear scar and surface integrity have been examined with help of several different characterization techniques, for example scanning electron microscopy and Auger electron spectroscopy.   The results showed that the PCBN cutting tools used displayed crater wear, flank wear and edge micro chipping. While the influence of the coating on the crater and flank wear was very small and the coating showed a high tendency to spalling. Scratch testing of coated PCBN showed that, the TiAlN coating resulted in major adhesive fractures. This displays the importance of understanding the effect of different types of lapping/grinding processes in the pre-treatment of hard and super hard substrate materials and the amount and type of damage that they can create. For the cutting tools used in turning, patches of a adhered layer, mainly consisting of FexOy were shown at both the crater and flank. And for the cutting tools used in milling a tribofilm consisting of SixOy covered the crater. A combination of tribochemical reactions, adhesive wear and mild abrasive wear is believed to control the flank and crater wear of the PCBN cutting tools. On a microscopic scale the difference phases of the PCBN cutting tool used in turning showed different wear characteristics. The machined surface of the work material showed a smooth surface with a Ra-value in the range of 100-200 nm for the turned surface and 100-150 nm for the milled surface. With increasing crater and flank wear in combination with edge chipping the machined surface becomes rougher and showed a higher Ra-value. For the cutting tools used in milling the tendency to micro edge chipping was significant higher when milling the tools steels showing a higher hard phase content and a lower heat conductivity resulting in higher mechanical and thermal stresses at the cutting edge.

In situ formation of BN nanotubes during nitriding reactions

High-yield multiwalled boron nitride (BN) nanotubes have been produced using a ball milling-annealing method. The BN nanotubes with a diameter less than 10 nm and a well-crystallized multiwalled structure were formed via an in situ nitriding reaction. The systematic investigation of the formation process at different annealing temperatures and for different times suggested that the formation of the unique multiwalled structure was attributed by a two-dimensional growth of the BN phase and a nonmetal catalytic growth.

One-dimensional nanomaterials synthesized using high-energy ball milling and annealing process

One-dimensional (1D) nanomaterials including nanotubes, nanowires and nanorods have many new properties, functionalities and a large range of promising applications. A major challenge for these future industrial applications is the large-quantity production. We report that the ball milling and annealing process has the potential to achieve the mass production. Several examples including C, BN nanotubes and SiC, Zn nanowires are presented to demonstrate such capability. In addition, both size and structure of 1D nanomaterials can be controlled by varying processing conditions. New growth mechanisms involved in the process have been investigated and the high-energy ball milling has an important role in the formation of these 1D nanomaterials.

Direct observation of defect levels in hexagonal BN by soft X-ray absorption spectroscopy

Formation of defects in hexagonal boron nitride under low-energy argon bombardment has been studied by near-edge X-ray absorption fine structure (NEXAFS) around B and N K-edges. Breaking of B-N bonds and creation of nitrogen vacancies has been identified from the B K-edge, followed by the formation of molecular nitrogen, N2, at interstitial positions. The presence of N2 produces a sharp resonance in the low-resolution NEXAFS spectra around N K-edge, showing the characteristic vibrational fine structure in high-resolution measurements. Several new peaks in NEXAFS spectra have been assigned to boron or nitrogen interstitials, in good agreement with theoretical predictions. © 2009 Elsevier B.V. All rights reserved.

Magnetism of C adatoms on BN nanostructures : implications for functional nanodevices

Spin-polarized density functional calculations reveal that magnetism can be induced by carbon adatoms on boron nitride nanotubes (BNNTs) and BN hexagonal sheets. As a result of the localization of impurity states, these hybrid sp-electron systems are spin-polarized, with a local magnetic moment of 2.0 μB per C adatom regardless of the tube diameter and the bonding between the C atom and the BNNTs/BN sheets. An analysis of orbital hybridization indicates that two valence electrons participate in the bonding and the remaining two electrons of the C adatom are confined at the adsorption site and contribute to the magnetism accordingly. The effective interaction distance between the C-induced magnetic moments is evaluated. In terms of the diffusion barrier and the adsorption energy of C adatoms on the BN nanotubes/ sheets, a fabrication method for BN-C-based functional nanodevices is proposed, and a series of virtual building blocks for functional devices are illustrated.

METHOD OF MANUFACTURE

A process for producing boron nitride nanotubes and nanotube films, which process comprises heating a liquid composition comprising boron particles and a metal compound, wherein heating takes place at a temperature of from 800-1300 DEG C in a gaseous atmosphere containing nitrogen that causes boron nitride nanotubes to grow, and wherein the boron particles have an average particle size of less than 100 nm, and wherein the metal compound is selected such that it promotes the growth of boron nitride nanotubes during heating.

Graphene quantum dots induce apoptosis, autophagy, and inflammatory response via p38 mitogen-activated protein kinase and nuclear factor-κB mediated signaling pathways in activated THP-1 macrophages.

The biomedical application of graphene quantum dots (GQDs) is a new emerging area. However, their safety data are still in scarcity to date. Particularly, the effect of GQDs on the immune system remains unknown. This study aimed to elucidate the interaction of GQDs with macrophages and the underlying mechanisms. Our results showed that GQDs slightly affected the cell viability and membrane integrity of macrophages, whereas GQDs significantly increased reactive oxygen species (ROS) generation and apoptotic and autophagic cell death with an increase in the expression level of Bax, Bad, caspase 3, caspase 9, beclin 1, and LC3-I/II and a decrease in that of Bcl-2. Furthermore, low concentrations of GQDs significantly increased the expression of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-8, whereas high concentrations of GQDs elicited opposite effects on the cytokines production. SB202190, a selective inhibitor of p38 mitogen-activated protein kinase (MAPK), abolished the cytokine-inducing effect of GQDs in macrophages. Moreover, GQDs significantly increased the phosphorylation of p38 MAPK and p65, and promoted the nuclear translocation of nuclear factor-κB (NF-κB). Taken together, these results show that GQDs induce ROS generation, apoptosis, autophagy, and inflammatory response via p38MAPK and NF-κB mediated signaling pathways in THP-1 activated macrophages.

Template-free synthesis of functional 3D BN architecture for removal of dyes from water.

Three-dimensional (3D) architectures are of interest in applications in electronics, catalysis devices, sensors and adsorption materials. However, it is still a challenge to fabricate 3D BN architectures by a simple method. Here, we report the direct synthesis of 3D BN architectures by a simple thermal treatment process. A 3D BN architecture consists of an interconnected flexible network of nanosheets. The typical nitrogen adsorption/desorption results demonstrate that the specific surface area for the as-prepared samples is up to 1156 m(2) g(-1), and the total pore volume is about 1.17 cm(3) g(-1). The 3D BN architecture displays very high adsorption rates and large capacities for organic dyes in water without any other additives due to its low densities, high resistance to oxidation, good chemical inertness and high surface area. Importantly, 88% of the starting adsorption capacity is maintained after 15 cycles. These results indicate that the 3D BN architecture is potential environmental materials for water purification and treatment.

Study and exploration on inorganic nanomaterials as additive in lubricant application.

 In this thesis, the application of planetary ball milling for the efficient production of nanomaterials is systematically studied. Three inorganic materials: calcium carbonate (CaCO3), molybdenum disulphide (MoS2) and hexagonal-boron nitride (h-BN) are chosen as model systems.