Recovering gallium from residual bayer process liquor

Gallium is normally obtained by direct electrolysis as a by-product from Bayer process residual liquor at an aluminum processing plant. However, to permit any net accumulation of the metal, the gallium concentration must be at least about 0.3 g/l in the liquor. This article describes a continuous process of extraction with organic solvents and rhodamine-B, followed by a re-extraction step into aqueous media. The final product is a solid containing up to 18 wt.% Ga in a solid mixture of hydroxides and oxides of gallium and aluminum. This final product can then be electrolyzed to recover the gallium more efficiently.     

The Structure of the Irreversibly Bound Adhesion Promoter-Substrate Interfacial Layer of γ-Aminopropylsilanetriol on Crystalline Si, as Measured by XPS and FTIR

The irreversibly bound interfacial layer deposited by the γ-aminopropysilanetriol adhesion promoter onto a crystalline silicon substrate, which remains even after profuse washing, was found by XPS to have resulted from the fragmentation and rearrangement of the original γ-aminopropylsilanetriol molecule. A mechanism is proposed, involving the homolytic scission of the terminal N-C bond. One of the subsequent reactions is believed to involve hydrogen loss by abstraction and the formation of a terminal vinyl group, which bonds to the substrate. Support for this mechanism is found in IR spectroscopy of this layer.     

Cu/SBA-15 as adsorbent for propane/propylene separation

Samples of mesoporous silica SBA-15 were prepared under hydrothermal conditions where Cu cations were incorporated to the structure by impregnation in order to compare the adsorption behavior in the presence and absence of this element. The adsorption/desorption equilibrium isotherms of propylene, propane, and N₂ were measured to evaluate their usefulness in the propane/propylene separation. All the adsorption isotherms of SBA-15 measured in the absence of Cu cations were described by the Freundlich equation, while the adsorption isotherms of propane on Cu/SBA-15 were better represented by the Henry equation and those of propylene were satisfactorily described by the Langmuir model in the range P < 100 Torr. The adsorption uptake of propylene increased and that of propane decreased in Cu/SBA-15 as compared to the amounts observed in the SBA-15 sample. The presence of Cu atoms in the adsorbent lattice increased the selectivity towards propylene. Under some working conditions the adsorbed amount of propylene in Cu/SBA-15 sample was totally reversible and the propane uptake, negligible.     

Factors influencing the formation of elongated morphologies in immiscible polymer blends during melt processing

The morphology of the dispersed phase in immiscible polymer blends plays an important role in the determination of the final physical properties. This paper considers factors that influence the final state of deformation of the dispersed phase, and in particular, the formation of fibers and lamellae. Blends of polyethylene and nylon-6 were extruded by ribbon extrusion at different draw ratios. Prior to single-screw extrusion the materials were blended in a co-rotating twin-screw extruder, and the size of the dispersed phase was studied as a function of the viscosity ratio. As the blends are extruded into ribbons and drawn through the calender rolls, the morphology of the dispersed phase undergoes drastic transformations. The fiber formation is enhanced by increasing the draw ratio. At high draw ratios, long thin fibers are observed. Some biaxial deformation is obtained for the noncompatibilized systems when the extruded materials enter the calender with the maximum closing pressure applied to the rolls. The same effect is observed for the compatibilized systems with lower values of the viscosity ratio. As a general rule, it has been observed that the final dispersed phase deformation is diminished in interfacially compatibilized systems.     

EXPERIMENTAL STUDY ON MIXING: POWER CONSUMPTION AND DEGREE OF SUSPENSION

An experimental study on mixing, degree of suspension and power consumption in solid-liquid suspensions was done. A system similar to those found in anaerobic fermentation processes of animal manures was used, and an existing mixing equipment was adapted for the study. Power consumption and degree of suspension for both mechanical mixing and mixing by gas was determined. The influence of variables such as geometry, solids concentration, stirrer velocity, and gas velocity was studied, discussed, and compared to data from the literature. Best results were obtained for gas mixing, the power consumption being about one fourth of that required by mechanical agitation. Finally, extended correlations relating Power and Reynolds numbers for mechanical mixing and mixing by gas are proposed.     

In vivo aging of gutta‐percha dental cone

Gutta‐percha cone is the most widely used material for root canal filling. The in vivo aging of this cone focus on the degradation of its main organic component, trans‐1,4‐polyisoprene, was studied. Aged cones (25 samples) from 2 to 30 years of root canal filling were extracted from different patients in the occasion of retreatment by mechanical way. The information about the aging time was given by the patients. Gel‐permeation chromatography (GPC) and infrared spectroscopy (FTIR) were the analytical techniques used. Polyisoprene degrades with time of aging, but in a slow process. Decrease in polymer molar mass from 5.7 × 10⁵ to 1.7 × 10⁵ g/mol was observed in polyisoprene from cone after 30 years of root canal filling and inside a noninfected tooth. In tooth with caries and periodontal infection, the decrease in molar mass is higher (4.6 × 10⁴ g/mol in cone with 10 years of aging). The production of carbonyl and hydroxyl groups in the aged material indicates that the process is oxidative, even in closed teeth. In these cases, the oxygen could be provided from tissue fluid. The degradation mechanism is complex and depends on many factors, besides time of root canal filling. The dental problem caused by the aging could be the production and migration of cytotoxic substances to periodontal ligament and the reduction on the canal sealing property due to the polymer weight loss. Both of them could contribute to the root canal treatment failure. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:4082–4088, 2006     

Semi-interpenetrating polymer networds produced with polyethylene terephthalate oligomer and unsaturated polyester resin

A series of semi-interpenetrating polymer networks (semi-IPN's) based on different compositions of an acyclic polyethylene terephthalate oligomer and unsaturated polyester resin (UP) were prepared. The oligomer was dissolved in the resin containing styrene crosslinker. Later this mixture was crosslinked at room temperature using methyl ethyl ketone peroxide catalyst and cobalt naphtanate as promoter. The tensile strength of the IPN's decreases as the concentration of oligomer increases, whereas, elongation to break increases. A characterization of the oligomer used is also presented.     

Decentralized observers with consensus filters for distributed discrete-time linear systems

This paper presents a decentralized observer with a consensus filter for the state observation of discrete-time linear distributed systems. Each agent in the distributed system has an observer with a model of the plant that utilizes the set of locally available measurements, which may not make the full plant state detectable. This lack of detectability is overcome by utilizing a consensus filter that blends the state estimate of each agent with its neighbors’ estimates. It is proven that the state estimates of the proposed observer exponentially converge to the actual plant states under arbitrarily changing, but connected, communication and pseudo-connected sensing graph topologies. Except these connectivity properties, full knowledge of the sensing and communication graphs is not needed at the design time. As a byproduct, we obtained a result on the location of eigenvalues, i.e., the spectrum, of the Laplacian for a family of graphs with self-loops.     

The morphology of MoS2, WS2, Co–Mo–S, Ni–Mo–S and Ni–W–S nanoclusters in hydrodesulfurization catalysts revealed by HAADF-STEM

HAADF-STEM studies have provided detailed morphological insight regarding MoS₂, WS₂, Co–Mo–S, Ni–Mo–S and Ni–W–S nanostructures in graphite-supported catalysts. It is found that the technique allows the catalytically active edges to be imaged even for single layer metal sulfide structures. Unpromoted MoS₂ and WS₂ are predominantly present as slightly truncated triangular clusters containing only a single S–M–S layer (M = Mo, W). The addition of promoter atoms results in more heavy truncations consistent with the expected tendency for the Co–Mo–S structures to expose promoted S-type edges at the expense of unpromoted Mo-type edges. However, the HAADF-STEM (High-Angle Annular Dark-field Scanning Transmission Electron Microscopy) results show for the first time that Co–Mo–S and Ni–W–S may also expose extended high index truncations.     

A 2D algorithm with asymmetric workload for the UPC conjugate gradient method

This paper examines four different strategies, each one with its own data distribution, for implementing the parallel conjugate gradient (CG) method and how they impact communication and overall performance. Firstly, typical 1D and 2D distributions of the matrix involved in CG computations are considered. Then, a new 2D version of the CG method with asymmetric workload, based on leaving some threads idle during part of the computation to reduce communication, is proposed. The four strategies are independent of sparse storage schemes and are implemented using Unified Parallel C (UPC), a Partitioned Global Address Space (PGAS) language. The strategies are evaluated on two different platforms through a set of matrices that exhibit distinct sparse patterns, demonstrating that our asymmetric proposal outperforms the others except for one matrix on one platform.