Quantitative analysis of a complex metal carbide formed during furnace cooling of cast duplex stainless steel using EELS and EDS in the TEM

In this work, a method to determine the atomic ratio of Mo and C within complex metal carbides using EELS in the TEM has been developed. The method is based on the determination of k-factors for given experimental conditions from the EEL spectra of Mo₂C and MoO₃ standards, which had been independently checked by XRD and EPMA. Factors affecting the k_Mo/C value of the Mo₂C standard were also investigated and the value was shown to be insensitive to background subtraction window width but sensitive to prolonged irradiation and specimen thicknesses above a critical value. The method and k-factor obtained from the Mo₂C standard was applied to spectra from a complex metal carbide precipitate formed during furnace cooling of a cast duplex stainless steel. Using EELS and EDS in the TEM, the composition was estimated to be (Cr_1.52Fe_2.33Mo_1.25Ni_0.17Si_0.46)C, which is close to M₆C stoichiometry, and the structure was confirmed by electron diffraction.     

Determining the local coordination of aluminium in cement using electron energy loss near-edge structure

The local site symmetry of aluminium in Al-substituted calcium silicate hydrate phases, similar to those found in hardened Portland cement pastes, has been determined by experimental measurement and theoretical modelling of the electron energy loss near-edge structure associated with the aluminium K-edge measured using parallel electron energy loss spectroscopy in the transmission electron microscope. Changes in the local aluminium environment were observed between different regions of the microstructure which are explained in terms of aluminium substitution into both tetrahedral silicon and octahedral magnesium sites. This spatially-resolved information is in excellent agreement with²⁷Al and²⁹Si magic angle spinning nuclear magnetic resonance data on bulk samples as well as the predictions based upon compositional trends derived from the results of energy dispersive X-ray and electron energy loss elemental microanalysis. In a wider context we wish to stress the complementarity of both spatially-resolved and bulk spectroscopic techniques, which possess differing degrees of sensitivity, in the analysis of materials science samples.     

Electrochemical modeling of the silica nanoparticle-biomembrane interaction

The interaction of amorphous colloidal silica (SiO(2)) nanoparticles of well-defined sizes with a dioleoyl phosphatidylcholine (DOPC) monolayer on a mercury (Hg) film electrode has been investigated. It was shown using electrochemical methods and microcalorimetry that particles interact with the monolayer, and the electrochemical data shows that the extent of interaction is inversely proportional to the particle size. Scanning electron microscopy (SEM) images of the electrode-supported monolayers following exposure to the particles shows that the nanoparticles bind to the DOPC monolayer irrespective of their size, forming a particle monolayer on the DOPC surface. A one-parameter model was developed to describe the electrochemical results where the fitted parameter is an interfacial layer thickness (3.2 nm). The model is based on the adsorptive interactions operating within this interfacial layer that are independent of the solution pH and solution ionic strength. The evidence implies that the most significant forces determining the interactions are van der Waals in character.     

Microwave plasma synthesis of lanthanide zirconates from microwave transparent oxides

Lanthanide zirconate phases Ln(2)Zr(2)O(7) and Ln(4)Zr(3)O(12) (Ln = Y, La, Gd, Dy, Ho, Yb) have been prepared using a microwave induced plasma methodology, which allows rapid synthesis using materials which do not couple directly with microwaves at room temperature. We describe the measurement of heating profiles of the precursor binary metal oxides which can be used to identify conditions conducive to the synthesis of more complex oxides. Uncontrolled heating which can be a feature of microwave synthesis of ceramics is not observed, allowing reproducible synthesis. Conventionally these phases are prepared at >1400 °C over hours or days and are being investigated for applications including the immobilisation of nuclear waste where rapid processing is important. Using the microwave plasma method, phase-pure materials have been prepared in minutes. Furthermore, it is clear that Ln(2)Zr(2)O(7) and Ln(4)Zr(3)O(12) also exhibit significant plasma-promoted dielectric heating (e.g. >2200 °C for Dy(4)Zr(3)O(12)) which is typically greater than either of the respective precursors, thus providing a driving force to rapidly complete the reaction.     

Quantitative characterization of nanoparticle agglomeration within biological media

The electronics industry is one of the world??s fastest growing manufacturing industries. However, e-waste has become a serious pollution problem. This study reports the recovery of e-waste for preparing valuable MCM-48 and ordered mesoporous carbon for the first time. Specifically, this study adopts an alkali-extracted method to obtain sodium silicate precursors from electronic packaging resin ash. The influence of synthesis variables such as gelation pH, neutral/cationic surfactant ratio, hydrothermal treatment temperature, and calcination temperature on the mesophase of MCM-48 materials is investigated. Experimental results confirm that well-ordered cubic MCM-48 materials were synthesized in strongly acidic and strongly basic media. The resulting mesoporous silica had a high surface area of 1,317?m²/g, mean pore size of about 3.0?nm, and a high purity of 99.87?wt%. Ordered mesoporous carbon with high surface area (1,715?m²/g) and uniform pore size of CMK-1 type was successfully prepared by impregnating MCM-48 template using the resin waste. The carbon structure was sensitive to the sulfuric acid concentration and carbonization temperature. Converting e-waste into MCM-48 materials not only eliminates the disposal problem of e-waste, but also transforms industrial waste into a useful nanomaterial.     

Synthesis of a new boron carbonitride with a B4C-like structure from the thermolysis of N-alkylated borazines

Thermolysis of N-trialkyl borazines at 500 degrees C produces homogeneous, amorphous boron carbonitride phases, whose compositions are dependent upon the borazine substituent, and whose structures are similar to that of icosahedral boron carbide, B4C.     

HREM of the [111] surfaces of iron oxide nanoparticles

Mixed phase Fe3O4-gamma-Fe2O3 (magnetite-maghemite) iron oxide nanoparticles have been fabricated by colloidal routes. HRTEM/HRSTEM images of the nanoparticles show the presence of [111] facets that terminate with enhanced contrast, which is shown to be caused by the presence of additional cations at the edges of the nanoparticles. HRTEM images were taken on a FEI CM200 FEGTEM, a JEOL 3100 with a LaB6 source, and a double aberration corrected JEOL-JEM 2200FS FEGTEM. The enhanced contrast effect was observed on the [111] surface atomic layers resolved using each machine. HRSTEM images, taken on an aberration corrected STEM, resolved enhanced contrast at specific surface sites. Exit wave reconstruction was also carried out on focal series taken on a double aberration corrected JEOL-JEM 2200FS and showed similar highly resolved enhanced contrast at specific surface cation sites. It is apparent that additional cations are occupying the [111] terminating layers of these nanoparticle surfaces. The use of different microscopes and techniques in this paper provides strong evidence that the enhanced contrast is a real effect and not an effect caused by microscope aberrations.