Synthetic and coordination chemistry of the heavier trivalent technetium binary halides: uncovering technetium triiodide.

Technetium tribromide and triiodide were obtained from the reaction of the quadruply Tc-Tc-bonded dimer Tc2(O2CCH3)4Cl2 with flowing HX(g) (X = Br, I) at elevated temperatures. At 150 and 300 °C, the reaction with HBr(g) yields TcBr3 crystallizing with the TiI3 structure type. The analogous reactions with flowing HI(g) yield TcI3, the first technetium binary iodide to be reported. Powder X-ray diffraction (PXRD) measurements show the compound to be amorphous at 150 °C and semicrystalline at 300 °C. X-ray absorption fine structure spectroscopy indicates TcI3 to consist of face-sharing TcI6 octahedra. Reactions of technetium metal with elemental iodine in a sealed Pyrex ampules in the temperature range 250-400 °C were performed. At 250 °C, no reaction occurred, while the reaction at 400 °C yielded a product whose PXRD pattern matches the one of TcI3 obtained from the reaction of Tc2(O2CCH3)4Cl2 and flowing HI(g). The thermal stability of TcBr3 and TcI3 was investigated in Pyrex and/or quartz ampules at 450 °C under vacuum. Technetium tribromide decomposes to Na{[Tc6Br12]2Br} in a Pyrex ampule and to technetium metal in a quartz ampule; technetium triiodide decomposes to technetium metal in a Pyrex ampule.

Changes in silver nanoparticles exposed to human synthetic stomach fluid: effects of particle size and surface chemistry.

The significant rise in consumer products and applications utilizing the antibacterial properties of silver nanoparticles (AgNPs) has increased the possibility of human exposure. The mobility and bioavailability of AgNPs through the ingestion pathway will depend, in part, on properties such as particle size and the surface chemistries that will influence their physical and chemical reactivities during transit through the gastrointestinal tract. This study investigates the interactions between synthetic stomach fluid and AgNPs of different sizes and with different capping agents. Changes in morphology, size and chemical composition were determined during a 30 min exposure to synthetic human stomach fluid (SSF) using Absorbance Spectroscopy, High Resolution Transmission Electron and Scanning Electron Microscopy (TEM/SEM), Dynamic Light Scattering (DLS), and Nanoparticle Tracking Analysis (NTA). AgNPs exposed to SSF were found to aggregate significantly and also released ionic silver which physically associated with the particle aggregates as silver chloride. Generally, the smaller sized AgNPs (<10nm) showed higher rates of aggregation and physical transformation than larger particles (75 nm). Polyvinylpyrrolidone (pvp)-stabilized AgNPs prepared in house behaved differently in SSF than particles obtained from a commercial source despite having similar surface coating and size distribution characteristics.

First evidence for the formation of technetium oxosulfide complexes: synthesis, structure and characterization.

The reaction of tetrabutylammonium pertechnetate with bis(trimethylsilyl) sulfide in solution was studied by UV-Visible spectroscopy and mass spectrometry. Experimental results and density functional calculations provide the first evidence for the formation of a TcO(3)S(-) precursor. Larger scale synthesis afforded a solid that was characterized by EDX and XANES spectroscopy. XANES showed the presence of technetium in tetravalent state. EDX indicated the solid contained technetium, sulfur and oxygen.

Alterations in physical state of silver nanoparticles exposed to synthetic human stomach fluid.

The bioavailability of ingested silver nanoparticles (AgNPs) depends in large part on initial particle size, shape and surface coating, properties which will influence aggregation, solubility and chemical composition during transit of the gastrointestinal tract. Citrate-stabilized AgNPs were exposed to synthetic human stomach fluid (SSF) (pH 1.5) and changes in size, shape, zeta potential, hydrodynamic diameter and chemical composition were determined during a 1h exposure period using Surface Plasmon Resonance (SPR), High Resolution Transmission Electron Microscopy/Energy Dispersive X-ray Spectroscopy (TEM/EDS), Dynamic Light Scattering (DLS) and X-ray Powder Diffraction (XRD) combined with Rietveld analysis. Exposure of AgNPs to SSF produced a rapid decrease in the SPR peak at 414nm and the appearance of a broad absorbance peak in the near infrared (NIR) spectral region. During exposure to SSF, changes in zeta potential, aggregation and morphology of the particles were also observed as well as production of silver chloride which appeared physically associated with particle aggregates.

Application of electron microscopy in the observation of technetium and technetium dioxide nanostructures.

Transmission electron microscopy (TEM) was applied to characterize the microstructure of Tc metal and technetium dioxide synthesized by the decomposition of NH(4)TcO(4). The morphology of the Tc metal and well-resolved TcO(2) particles were characterized using bright-field TEM and scanning TEM modes. Structural characterization of these two samples using high-resolution (HR) TEM was successfully performed for the first time on the nanoscale. The morphology of Tc metal showed significant differences when compared to TcO(2). The crystal structure of Tc metal on the nanoscale was shown to contain well-resolved lattice fringes without any defects. Because of the deficiency in point resolution, however, the two-dimensional structure details of Tc metal could not be observed as expected. On the other hand, structural details of TcO(2) were prominent at high resolution. With a 2-fold multiplicity in both directions, TcO(2) showed a unique atomic distribution corresponding to a monoclinic unit cell. Furthermore, the lattice parameters of the samples were refined by the Rietveld analysis of the powder X-ray diffraction patterns and were estimated by HRTEM. In the case of technetium dioxide, the stoichiometry was approximated to be TcO(2.3) using quantitative analysis of X-ray energy dispersive spectrometry. Electron energy-loss spectrometry verified the chemical phase of the two samples by their different chemical environments based on an energy shift of 2.0 eV of the N(23) edge between TcO(2) and Tc metal.

Micro-structural characterization of precipitation-synthesized fluorapatite nano-material by transmission electron microscopy using different sample preparation techniques.

Fluorapatite is a naturally occurring mineral of the apatite group and it is well known for its high physical and chemical stability. There is a recent interest in this ceramic to be used as a radioactive waste form material due to its intriguing chemical and physical properties. In this study, the nano-sized fluorapatite particles were synthesized using a precipitation method and the material was characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Two well-known methods, called solution-drop and the microtome cutting, were used to prepare the sample for TEM analysis. It was found that the microtome cutting technique is advantageous for examining the particle shape and cross-sectional morphology as well as for obtaining ultra-thin samples. However, this method introduces artifacts and strong background contrast for high-resolution transmission electron microscopy (HRTEM) observation. On the other hand, phase image simulations showed that the solution-drop method is reliable and stable for HRTEM analysis. Therefore, in order to comprehensively analyze the microstructure and morphology of the nano-material, it is necessary to combine both solution-drop and microtome cutting techniques for TEM sample preparation.

Comparison of different sample preparation techniques in TEM observation of microstructure of INCONEL alloy 783 subjected to prolonged isothermal exposure.

INCONEL alloy 783 was annealed and aged following the standard heat treatment procedure. One set of specimens was then isothermally exposed at 500 degrees C for 3000 h. Mechanical properties were measured at room temperature and 650 degrees C, and the results showed the prolonged exposure increased the strength and decreased elongation of alloy 783. The microstructures of as-produced and exposed material were examined using optical microscope, SEM and TEM, respectively. Three techniques, jet electro-polishing, ion milling, and focused ion beam, were employed to prepare the TEM samples to observe the variation of microstructure of alloy 783 due to isothermal exposure. TEM images of samples prepared by different methods were analyzed and compared. The results indicate that the jet electro-polishing technique allows the detail microstructure of alloy 783 subjected to different treatments to be well revealed, and thereby the TEM images can be used to explain the enhancement of strength of alloy 783 caused by isothermal exposure.