NANOMECHANICAL AND SCALING BEHAVIOR OF NANOPOROUS GOLD

Nanoporous metals have recently been drawn significant interest in various fields of research. Their high surface-to-volume ratio present a strong potential for applications in sensing, catalysis, micro-electromechanical systems (MEMS) and even in the medical field. However, the mechanical properties of nanoporous metals have not yet been well determined, as conducting mechanical tests was found to be challenging. Scaling relations linking the mechanical properties of porous materials to those of their dense counterparts are successfully and widely used for many porous metals. However, their applicability to nanoporous metals have recently been questioned, as estimations from the classic scaling relations were found no to agree with experimental determinations. In this study, the mechanical properties of nanoporous gold will be measured by conducting tensile testing of single crystalline, millimeter-scale specimens, for the first time. Results did not agree with the predictions from the classic scaling relations. Using experimental results from these tensile tests, new nanoindentation testing and data reported in the literature, a new scaling relation for the yield strength of nanoporous gold is proposed. This new relation is found to correctly describe the mechanical properties of nanoporous gold. In addition, compression tests are conducted on polycrystalline nanoporous gold, and the results were found to agree very well with the proposed scaling relation

Pore Functionalized PVDF Membranes with In-Situ Synthesized Metal Nanoparticles: Material Characterization, and Toxic Organic Degradation

Functionalized PVDF membrane platforms were developed for environmentally benign in-situ nanostructured Fe/Pd synthesis and remediation of chlorinated organic compounds. To prevent leaching and aggregation, nanoparticle catalysts were integrated into membrane domains functionalized with poly (acrylic acid). Nanoparticles of 16–19 nm were observed inside the membrane pores by using focused ion beam (FIB). This technique prevents mechanical deformation of the membrane, compared to the normal SEM preparation methods, thus providing a clean, smooth surface for nanoparticles characterization. This allowed quantification of nanoparticle properties (size and distribution) versus depth underneath the membrane surface (0–20 μm). The results showed that nanoparticles were uniformly sized and evenly distributed inside the membrane pores. However, the size of nanoparticles inside the membrane pores was 13.9% smaller than those nanoparticles located on the membrane surface. Investigating nanoparticles inside membrane pores increases the accuracy of kinetic analysis and modeling aspects. Furthermore, the Fe/Pd immobilized membranes showed excellent performance in the degradation of chlorinated organics: Over 96% degradation of 3,3\u27,4,4\u27,5-pentachlorobiphenyl (PCB 126) was achieved in less than 15 s residence time in convective flow mode. The regeneration and reuse of this catalytic membrane system were also studied. Particles were examined in XRD upon formation, after deliberate oxidation, and after regeneration. The regenerated sample showed the same crystalline pattern as the original sample. Repeated degradation experiments demonstrated successful PCB 126 dechlorination with nanoparticles regenerated for four cycles with only a small loss in reactivity. It demonstrated that Fe/Pd immobilized membranes have the potential for large-scale remediation applications

Gadolinium Enrichment in Association with the Magnetic Fraction of 1 Fly Ash: Real or an Illusion?

Gadolinium, and possibly praseodymium, are relatively enriched in the magnetic 24 fractions of Class F fly ashes from Central Appalachian coal sources. Although the enrichment is 25 evident in the inductively coupled plasma–atomic emission spectroscopy (ICP-AES) 26 determinations of the rare earth content, transmission electron microscopy–energy dispersive x-27 ray spectroscopy (TEM-EDS) examination of the fly ash fails to show the sites of the Gd or Pr. 28 This apparent lack of correlation could be due to the inability of the EDS to detect low 29 concentrations of the rare earth elements definitively; interferences in the analytics, leading to 30 false positives in the chemical analysis; or the overlap of the energies of Gd and/or Pr with more 31 abundant elements, leading to inaccurate negative results

Nano-Scale Rare Earth Distribution in Fly Ash Derived from the Combustion of the Fire Clay Coal, Kentucky

Fly ash from the combustion of eastern Kentucky Fire Clay coal in a southeastern United States pulverized-coal power plant was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). TEM combined with elemental analysis via energy dispersive X-ray spectroscopy (EDS) showed that rare earth elements (REE; specifically, La, Ce, Nd, Pr, and Sm) were distributed within glassy particles. In certain cases, the REE were accompanied by phosphorous, suggesting a monazite or similar mineral form. However, the electron diffraction patterns of apparent phosphate minerals were not definitive, and P-lean regions of the glass consisted of amorphous phases. Therefore, the distribution of the REE in the fly ash seemed to be in the form of TEM-visible nano-scale crystalline minerals, with additional distributions corresponding to overlapping ultra-fine minerals and even true atomic dispersion within the fly ash glass

High-Resolution Transmission Electron Microscopy Study of a Powder River Basin Coal-Derived Fly Ash

Examination of a fly ash derived from the combustion of a low-S, subbituminous Powder River Basin coal by Scanning Electron Microscopy (SEM) and High-resolution Transmission Electron Microscopy (HRTEM), both supplemented by Energy-dispersive X-ray spectroscopy (EDS), showed that the fly ashes were dominated by amorphous phases, Ca-rich plagioclase feldspars, Mg-rich phases, complex Ca-Mg-Al-Si-Ti-Fe grains, and trace amounts of REE-rich particles. Many of the particles were rimmed by a Ca-S, possibly a sulfate. HRTEM-EDS examination of a REE-rich particle proved it to be a mix of light- and heavy-rare earth minerals mixed with amorphous phases

Nano-Scale Rare Earth Distribution in Fly Ash Derived from the Combustion of the Fire Clay Coal, Kentucky

Fly ash from the combustion of eastern Kentucky Fire Clay coal in a southeastern United States pulverized-coal power plant was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). TEM combined with elemental analysis via energy dispersive X-ray spectroscopy (EDS) showed that rare earth elements (REE; specifically, La, Ce, Nd, Pr, and Sm) were distributed within glassy particles. In certain cases, the REE were accompanied by phosphorous, suggesting a monazite or similar mineral form. However, the electron diffraction patterns of apparent phosphate minerals were not definitive, and P-lean regions of the glass consisted of amorphous phases. Therefore, the distribution of the REE in the fly ash seemed to be in the form of TEM-visible nano-scale crystalline minerals, with additional distributions corresponding to overlapping ultra-fine minerals and even true atomic dispersion within the fly ash glass