Graded evolution of anisotropic microstructure during sintering from crystal-oriented powder compact

Anisotropic sintering, including shrinkage and grain growth, was examined for c-axis-oriented (Sr,Ca)₂NaNb₅O₁₅ (SCNN) ceramics, which were prepared by colloidal processing under a magnetic field. In the c-axis-oriented SCNN powder compact, shrinkage and grain growth along the c-axis were higher than those along the a-axis. The anisotropic microstructural development was clearly associated with anisotropic sintering shrinkage. X-ray diffraction, scanning electron microscopy, and energy back scattering diffraction showed that the grain growth of oriented particles by including random grains contribute to the development of the oriented microstructure. Finally, the highly crystal-oriented SCNN ceramics with a densified microstructure were obtained through anisotropic sintering. These results clearly showed the potential to develop a well-defined anisotropic microstructure during sintering by designing and controlling the particle packing structure in a powder compact.     

On the use of 2-D coding techniques for ECG signals.

This paper discusses the convenience of using two-dimensional (2-D) coding techniques for the compression of electrocardiogram (ECG) signals. These signals present a very clear periodicity that can be exploited by the use of a 2-D time/frequency transform to decorrelate it as much as possible. A brief theoretical approach is given to justify the use of this technique, and a comparison is made between a 2-D and a one-dimensional (1-D) uniform quantization scenarios. The influence of the error as well as the frame size on the estimation of the fundamental period is studied.     

The impacts of a GTL plant on Brazil's oil products supply and refinery expansion

This paper assesses the impacts of a GTL plant on the expansion of Brazil's oil refining segment. The GTL plant (50,000 bpd) was sized to start up operations in 2015, producing diesel and naphtha through the indirect route (FT-synthesis). This plant will consume the non-associated natural gas production from the recent discoveries at the Santos Basin (around 419 Bm³), and the associated gas production from the Campos Basin. Both basins are located in the Southeast of Brazil, the most populated, rich and industrialized region of the country. Two different criteria for refinery expansion were simulated in order to meet oil product demand scenarios. Findings show that depending on the refinery expansion criteria considered GTL will play a fundamental hole to meet the oil product demand forecast to Brazil in the next 10 years.     

Influence of the counter-ion on the effective charge of polyacrylic acid in dilute condition

Osmotic pressure measurements were satisfactorily used to compute the effective charge of poly(acrylic) acid (PAA) at different pHs and with different monovalent and divalent counterions. This experimental method is sensitive to the osmotically active species (polymer and counterions). After correction for the polymer contribution to the total osmotic pressure (solvency and excluded volume), the remaining pressure can be attributed to the polyelectrolyte counterions and processed with Donnan and equation of state in order to compute the effective charge number per polymeric chain (Z^eff). The behavior of Z^eff against the chain concentration and pH was investigated after neutralization of PAA with LiOH, NaOH, and TMAOH. The results clearly indicate that the nature of the monovalent counterion has no effect on Z^eff leading to the conclusion that the interaction between monovalent counterions and the acrylate functionality is purely electrostatic in agreement with conductimetric and potentiometric results reported in the literature. The behavior of Z^eff against the degree of ionization of the polymer and its concentration is also in good agreement with the theoretical expectations of the theory of ionic condensation. Osmotic measurements were also used in order to understand the influence of divalent cations (Mg²⁺, Ca²⁺, Ba²⁺) on Z^eff of the sodium salt of PAA at pH 9 and at different divalent/acrylate molar ratio. All the divalent cations depress Z^eff each of one at different degrees, confirming a specific divalent/polymer interaction. The energy of hydration of cations can explain most of the observed results with divalents.     

Infrared and ultraviolet–visible spectroscopic studies of silica, [(Cp)2ZrCl2] and trimethylaluminum interactions

Infrared and UV–vis studies of metallocene immobilization on silica are reported here. The results have indicated changes in the Zr coordination sphere of metallocene depending on the immobilization route used. The reaction of [(Cp)₂ZrCl₂] with silica formed [(Cp)₂ZrCl]⁺[SiO]⁻ species. The same metallocene, reacting with TMA modified silica, formed monomethylated and dimethylated species by the substitution of chloro for methyl ligands, stabilized on the surface by interaction with “MAO-like” species (methylaluminoxane, MAO). These monomethylated and dimethylated cationic zirconium species are the active centers for the polymerization reaction. Different order of TMA addition in the silica modification step generated surface species of a similar nature, differing in their relative quantities. The highest amount of these active species was obtained when the support was added to the TMA solution rather than adding the TMA solution to the silica support. This was the most significant parameter affecting catalytic activity in ethylene polymerization.