Suitable Glass-Ceramic Sealant for Planar Solid-Oxide Fuel Cells

Various glass-ceramics were prepared based on the BaO–Al₂O₃–B₂O₃–SiO₂ system with the addition of La₂O₃, ZrO₂, or NiO in an attempt to develop a suitable sealant for planar solid-oxide fuel cells operating at 800°C. To estimate the applicability of these glasses as suitable sealants, their thermal and chemical stabilities as well as the crystallization behavior and bonding characteristics of their parent glasses were investigated. The thermal properties and crystallization behavior of the parent glasses were dependent on the type of additive used, and the bonding characteristics were strongly influenced by the B₂O₃/SiO₂ value in the glass composition. Observation of microstructural change and chemical reaction at the glass-ceramic/electrolyte interface confirmed that the prepared glass-ceramics possessed long-term stability during heat treatment at the operation temperature for up to 1000 h.     

Synthesis and characterization of new alkali-soluble polyimides and preparation of alternating multilayer nano-films therefrom

New alkali-soluble aromatic polyimides were prepared by a direct one-step polycondensation of 3,6-di(4-carboxyphenyl)pyromellitic dianhydride with common aromatic diamines in the presence of isoquinoline at 170 °C. The obtained polymers with inherent viscosities of the 0.62-1.01 g/dl range were all amorphous and highly soluble in dilute aqueous NaOH and tetramethylammonium hydroxide. Upon heating in TGA, the carboxylic acid groups degraded away at lower temperatures and the chain backbone did at higher temperatures. In DSC, no glass transition could be detected before decomposition. The alternating multilayer nano-films from the polyimides and poly(ethyleneimine) were prepared by the molecular self-assembly method and characterized by ellipsometry and X-ray reflectivity.     

Triphenylsulfonium salt methacrylate bound polymer resist for electron beam lithography

A new photoacid generator (PAG) bound polymer containing triphenylsulfonium salt methacrylate (TPSMA) was synthesized and characterized. The PAG bound polymer was employed to improve electron beam lithographic performance, including sensitivity and resolution. The PAG bound polymer resist exhibited a higher sensitivity (120 μC/cm²) than the PAG blend polymer resist (300 μC/cm²). Eliminating the post exposure baking process during development improved the resolution due to decreased acid diffusion. A high-resolution pattern fabricated by electron beam lithography had a line width of 15 nm and a high aspect ratio. The newly developed patterns functioned well as masks for transferring patterns on Si substrates by reactive ion etching.     

Dynamic visualization of crack propagation and bridging stress using the mechano-luminescence of SrAl2O4: (Eu,Dy,Nd)

The goal of the present investigation was to visualize the propagating crack in a mechano-luminescence (ML) material to enable the measurement of instantaneous R-curves and directly observe the bridging (shielding) stress in a fast-propagating crack system. The well-known ML compound, SrAl₂O₄: Eu²⁺, was used as a model test material. Two additional trivalent rare earth elements, Dy and Nd, were introduced as co-dopants to improve the luminescent efficiency. The initiation and growth of a crack from the mechanically machined sharp notch tip in a disc shaped compact tension (CT) specimen at a relatively high loading rate were found to be associated with the extent of light emission around the crack. An in-situ measurement of crack length and applied load for 0.3 sec yielded an instantaneous R-curve at the conventional crack propagation speed.     

Humic acid-induced silver nanoparticle formation under environmentally relevant conditions

The formation of silver nanoparticles (AgNPs) via reduction of silver ions (Ag(+)) in the presence of humic acids (HAs) under various environmentally relevant conditions is described. HAs tested originated from the Suwannee River (SUW), and included samples of three sedimentary HAs (SHAs), and five soils obtained across the state of Florida. The time required to form AgNPs varied depending upon the type and concentration of HA, as well as temperature. SUW and all three SHAs reduced Ag(+) at 22 °C. However, none of the soil HAs formed absorbance-detectable AgNPs at room temperature when allowed to react for a period of 25 days, at which time experiments were halted. The appearance of the characteristic surface plasmon resonance (SPR) of AgNPs was observed by ultraviolet-visible spectroscopy in as few as 2-4 days at 22 °C for SHAs and SUW. An elevated temperature of 90 °C resulted in the accelerated appearance of the SPR within 90 min for SUW and all SHAs. The formation of AgNPs at 90 °C was usually complete within 3 h. Transmission electron microscopy and atomic force microscopy images showed that the AgNPs formed were typically spherical and had a broad size distribution. Dynamic light scattering also revealed polydisperse particle size distributions. HAs appeared to colloidally stabilize AgNPs based on lack of any significant change in the spectral characteristics over a period of two months. The results suggest the potential for direct formation of AgNPs under environmental conditions from Ag(+) sources, implying that not all AgNPs observed in natural waters today may be of anthropogenic origin.