Characterization of nano-scale particles in hot-rolled, high strength low alloy steels (HSLA)

The contribution of nano-scale particles observed using Atom Probe Tomography in an increase of yield strength of conventional and advanced HSLA steels was studied. The advanced HSLA steel showed higher yield strength than conventional HSLA steel. There were two types of carbides, which primarily contribute to an increase in yield strength of conventional HSLA steel: (i) coarse TiC with average size of 25±5nm and (ii) fine TiC with average radius of 3±1.2nm. The presence of two types of carbides was found in the microstructure of advanced HSLA steel: (i)
nano-scale Ti0.98Mo0.02C0.6 carbides with average radius of 2.2±0.5nm, and (ii) C19Cr7Mo24 particles with an average radius of 1.5±0.3nm. The contribution of precipitation hardening in the yield strength of advanced HSLA steel due to the nano-scale particles was 174MPa, while this value in the conventional HSLA steel was 128MPa.

Application of advanced analytical techniques to study structure-property relationship of hot rolled high strength low alloy steel

The microstructure-property relationship in conventional high strength low alloy (HSLA) steel was evaluated using data obtained from transmission electron microscopy (TEM) and atom probe tomography (APT). Atom probe tomography allowed the characterisation of fine TiC particles with average radius of 3±1·2 nm that were not observed by TEM. The increase in the yield strength of steel due to the presence of fine precipitates was calculated to be 128 MPa.

Transmission electron microscopy characterization of the bake-hardening behavior of transformation-induced plasticity and dual-phase steels

The effect of prestraining (PS) and bake hardening (BH) on the microstructures and mechanical properties has been studied in transformation-induced plasticity (TRIP) and dual-phase (DP) steels after intercritical annealing. The DP steel showed an increase in the yield strength and the appearance of the upper and lower yield points after a single BH treatment as compared with the as-received condition, whereas the mechanical properties of the TRIP steel remained unchanged. This difference appears to be because of the formation of plastic deformation zones with high dislocation density around the “as-quenched” martensite in the DP steel, which allowed carbon to pin these dislocations, which, in turn, increased the yield strength. It was found for both steels that the BH behavior depends on the dislocation rearrangement in ferrite with the formation of cell, microbands, and shear band structures after PS. The strain-induced transformation of retained austenite to martensite in the TRIP steel contributes to the formation of a complex dislocation structure.

Light emission and excitonic effect of boron nitride nanotubes observed by photoluminescent spectra

Photoluminescent (PL) and optical absorption spectra of high-yield multi-wall BN nanotubes (BNNTs) were systematically investigated at room temperature in comparison with commercial hexagonal BN (h-BN) powder. The direct band gap of the BNNTs was determined to be 5.75 eV, just slightly narrower than that of h-BN powder (5.82 eV). Two Frenkel excitons with the binding energy of 1.27 and 1.35 eV were also determined. However, they were not a distinctive characteristic of the BNNTs as reported previously. Observed broad UV–visible–NIR light emission demonstrates the potential of the BNNTs as a nano light source.

Field-emission characteristics of conical boron nitride nanorods

We present the electron field-emission (FE) characteristics of conical boron nitride nanorods grown on a (1 0 0) n-type silicon substrate. The emission current can be up to ~60 µA at an applied voltage of ~3 kV. Two distinct slopes are evident in the Fowler–Nordheim (FN) plot. The FE characteristics can be explained using a site-related tunnelling-controlled mechanism. The occurrence of two FN slopes is attributed to the switchover from tip emission to side emission, which results from the differences in interface barrier, geometry, as well as the total emission area of the two emission interfaces.

Dual responsive chemosensors for anions : the combination of fluorescent PET (Photoinduced Electron Transfer) and colorimetric chemosensors in a single molecule

The design and synthesis of two novel fluorescent PET anion sensors is described, based on the principle of ‘fluorophore-spacer-(anion)receptor’. The sensors 1 and 2 employ simple diaromatic thioureas as anion receptors, and the fluorophore is a naphthalimide moiety that absorbs in the visible part of the spectrum and emits in the green. Upon recognition of anions such as F⁻ and AcO⁻ in DMSO, the fluorescence emission of 1 and 2 was ‘switched off’, with no significant changes in the UV–vis spectra. This recognition shows a 1:1 binding between the receptor and the anions. In the case of F⁻, further additions of the anion, gave rise to large changes in the UV–vis spectra, where the λ_max at 455 nm was shifted to 550 nm. These changes are thought to be due to the deprotonation of the 4-amino moiety of the naphthalimide fluorophore. This was in fact found to be the case, using simple naphthalimide derivatives such as 6. Sensors 1 and 2 can thus display dual sensing action; where at low concentrations, the fluorescence emission is quenched, and at higher concentrations the absorption spectra are modulated.

A surface characterisation and microstructural study by scanning electron microscopy of the N-methyl-n-alkylpyrrolidinium tetrafluoroborate organic salts

A microstructural characterisation of the family of N-methyl-N-alkylpyrrolidinium tetrafluoroborate organic salts was carried out by observation of powder surface morphologies with the aim of extending the microstructure-property correlation. Inherent difficulties limiting extensive studies of organic solids by SEM, including volatility under vacuum, charging due to electron beam irradiation, and air-sensitivity were overcome with the use of a Field Emission SEM and cryostage attachment. This technique, providing considerable improvements in image quality at low accelerating voltages, enabled direct observation of complex microstructural features in samples exhibiting high temperature plastic crystalline phases (N,N-dimethylpyrrolidinium tetrafluoroborate [P11BF4]; N-methyl-N-ethylpyrrolidinium tetrafluoroborate [P12BF4]; N-methyl-N-propylpyrrolidinium tetrafluoroborate [P13BF4]). Extensive lattice imperfections including grain boundaries, slip planes and dislocation pits were observed within particles of approximately 200 mgrm diameter. The N-methyl-N-butylpyrrolidinium tetrafluoroborate (P14BF4) sample in this series revealed columnar single crystals with high aspect ratios. The origin of plastic flow properties is discussed using single crystal and polycrystalline slip observations and a relationship proposed between defect characteristics and transport properties.

A comparative study of secondary Ion emission from water ice under Ion bombardment by Au+, Au3+, and C60+

Secondary ion emission from water ice has been studied using Au⁺, Au₃⁺, and C₆₀⁺ primary ions. In contrast to the gas phase in which the spectra are dominated by the (H₂O)_nH⁺ series of ions, the spectra from ice using all three primary ions are principally composed of two series of cluster ions (H₂O)_nH⁺ and (H₂O)_n⁺. Dependent on the conditions, the unprotonated series can dominate the spectra. Since in the gas phase (H₂O)_n⁺ is unstable with respect to the formation of the protonated ion series, the presence of the solid must provide a means to stabilize their formation. The cluster ion yields under Au⁺ bombardment are very low and can be understood in terms of sputtering on the borderline between linear cascade and thermal spike behavior. There is a 10⁴ increase in yield across the whole spectrum compared to Au⁺ when Au₃⁺ and C₆₀⁺ species are used as primary ions. The character of the spectra differed between these two primary ions, but insights into the mechanism of secondary ion emission for both is discussed within an energy deposition framework provided by the fluid flow-based mesoscale energy deposition footprint (MEDF) model that predicts a cone-shaped zone of activation and emission. C₆₀⁺ differs from Au^₃+ in that it delivers its energy closer to the surface, and it is argued this has consequences for the cluster ion distribution and yield. Increasing the ion dose by sputtering suppresses the yield of (H₂O)_n⁺ and increases the yield of the protonated ions in the small cluster region, whereas the yield in the large cluster regime is suppressed significantly. The three primary ions show rather different behavior, and this is discussed in the light of the sputtering models. Finally, negative ion spectra including cluster ions have been observed for the first time. C₆₀⁺ delivers the highest yields, but these are less than 10 times the positive ion yields, probably because the O and OH fragment ions on which the clusters are based are easily neutralized by protons.

Simultaneous control of spectroscopic and electrochemical properties in functionalised electrochemiluminescent tris(2,2'-bipyridine)ruthenium(II) complexes

Using a combination of electrochemical, spectroscopic and computational techniques, we have explored the fundamental properties of a series of ruthenium diimine complexes designed for coupling with other molecules or surfaces for electrochemiluminescence (ECL) sensing applications. With appropriate choice of ligand functionality, it is possible to manipulate emission wavelengths while keeping the redox ability of the complex relatively constant. DFT calculations show that in the case of electron withdrawing substituents such as ester or amide, the excited state is located on the substituted bipyridine ligand whereas in the case of alkyl functionality it is localised on a bipyridine. The factors that dictate annihilation ECL efficiency are interrelated. For example, the same factors that determine ΔG for the annihilation reaction (i.e. the relative energies of the HOMO and LUMO) have a corresponding effect on the energy of the excited state product. As a result, most of the complexes populate the excited state with an efficiency (Φex) of close to 80% despite the relatively wide range of emission maxima. The quantum yield of emission (Φp) and the possibility of competing side reactions are found to be the main determinants of ECL intensity.

Electron backscatter diffraction (EBSD) map of AZ31 compressed to 1% strain at room temperature in a direction parallel to the extrusion direction

The collection contains an EBSD map of AZ31 compressed to 1% strain at room temperature in a direction parallel to the extrusion direction. The map was collected as part of an investigation into the role of twinning in the occurrence of a yield point elongation during deformation.

An impaired mitochondrial electron transport chain increases retention of the hypoxia imaging agent diacetylbis(4-methylthiosemicarbazonato)copper II

Radiolabeled diacetylbis(4-methylthiosemicarbazonato)copper^II [Cu^II(atsm)] is an effective positron-emission tomography imaging agent for myocardial ischemia, hypoxic tumors, and brain disorders with regionalized oxidative stress, such as mitochondrial myopathy, encephalopathy, and lactic acidosis with stroke-like episodes (MELAS) and Parkinson’s disease. An excessively elevated reductive state is common to these conditions and has been proposed as an important mechanism affecting cellular retention of Cu from Cu^II(atsm). However, data from whole-cell models to demonstrate this mechanism have not yet been provided. The present study used a unique cell culture model, mitochondrial xenocybrids, to provide whole-cell mechanistic data on cellular retention of Cu from Cu^II(atsm). Genetic incompatibility between nuclear and mitochondrial encoded subunits of the mitochondrial electron transport chain (ETC) in xenocybrid cells compromises normal function of the ETC. As a consequence of this impairment to the ETC we show xenocybrid cells upregulate glycolytic ATP production and accumulate NADH. Compared to control cells the xenocybrid cells retained more Cu after being treated with Cu^II(atsm). By transfecting the cells with a metal-responsive element reporter construct the increase in Cu retention was shown to involve a Cu^II(atsm)-induced increase in intracellular bioavailable Cu specifically within the xenocybrid cells. Parallel experiments using cells grown under hypoxic conditions confirmed that a compromised ETC and elevated NADH levels contribute to increased cellular retention of Cu from CuII(atsm). Using these cell culture models our data demonstrate that compromised ETC function, due to the absence of O2 as the terminal electron acceptor or dysfunction of individual components of the ETC, is an important determinant in driving the intracellular dissociation of Cu^II(atsm) that increases cellular retention of the Cu.

Wootz steel project by electron backscatter diffraction

The data is from an electron backscatter diffraction (EBSD) study of the microstructure of high carbon ‘Wootz’ steel. The objective of the study is to infer an unknown thermomechanical history from observation and analysis of the final microstructure in various ancient artefacts (swords and tools), and then compare the findings with heat treatments of the ancient artefacts and modern attempts at duplication of the structure. Electron backscatter data reveals the orientation relationships between various phases in the material, particularly cementite and ferrite. The dataset is randomly structured and organised. The data is automatically generated by an electron backscattered diffraction system attached to a field emission scanning electron microscope. The dataset uses proprietary software (cannot be copied or distributed without complying with licensing agreements): Oxford HKL Channel 5. As the native formats are binary they cannot be read with standard software.

Annihilation electrogenerated chemiluminescence of mixed metal chelates in solution : Modulating emission colour by manipulating the energetics

We demonstrate the mixed annihilation electrogenerated chemiluminescence of tris(2,2′-bipyridine)ruthenium(ii) with various cyclometalated iridium(iii) chelates. Compared to mixed ECL systems comprising organic luminophores, the absence of T-route pathways enables effective predictions of the observed ECL based on simple estimations of the exergonicity of the reactions leading to excited state production. Moreover, the multiple, closely spaced reductions and oxidations of the metal chelates provide the ability to finely tune the energetics and therefore the observed emission colour. Distinct emissions from multiple luminophores in the same solution are observed in numerous systems. The relative intensity of these emissions and the overall emission colour are dependent on the particular oxidized and reduced species selected by the applied electrochemical potentials. Finally, these studies offer insights into the importance of electronic factors in the question of whether the reduced or oxidized partner becomes excited in annihilation ECL. This journal is

Field emission properties from boron nitride nanotube field emitters

Boron nitride nanotubes (BNNTs) have been studied as a field emission material due to their unique and excellent properties such as high oxidation resistance and negative electron affinity. However, field emission properties of BNNT field emitters were rarely reported until now because it is difficult to synthesize high purity BNNTs and fabricate stable BNNT field emitters. Here, we report high field emission properties from BNNT field emitters fabricated on a tungsten rod.