Platinum-alloy nanostructured thin film catalysts for the oxygen reduction reaction

In an effort to study advanced catalytic materials for the oxygen reduction reaction (ORR), a number of metallic alloy nanostructured thin film (NSTF) catalysts have been characterized by rotating disk electrode (RDE). Optimal loadings for the ORR and activity enhancement compared to conventional carbon supported nanoparticles (Pt/C) were established. The most efficient catalyst was found to be PtNi alloy with 55 wt% of Pt. The enhancement in specific activity is more than one order of magnitude, while the improvement factor in mass activity is 2.5 compared to Pt/C. Further lowering of the platinum to nickel ratio in NSTF catalysts did not lead to increased mass activity values.     

Synthesis of mesoporous silica particles with controlled pore structure

Silica particles, with controllable porosity, were synthesized using two different precursors, tetraethylortosilicate (TEOS) and sodium silicate, but without the addition of template. Characteristics of silica particles (aggregates) prepared by these two methods were compared. The pore structure was tuned only by changing the processing parameters, such as precursor concentration, base concentration, temperature and reaction time. The pore structure of prepared silica particles (aggregates) is strongly influenced by processing conditions and easy controllable in broad range of the specific surface area, pore size, size distribution and pore volume. However, the silica particles synthesized from TEOS have very low total pore volume (ranging from 0.06 to 0.2 cm³/g) and a large portion of pores smaller than 4 nm. On the other side, the silica particles prepared from sodium silicate can be defined as a mesoporous silica with the average pore size up to 20 nm and much higher total pore volume (ranging from 0.8 to 1.5 cm³/g), which are important advantages for their application in encapsulation of enzymes.     

Multilevel control of mechanical multivariable systems as applied to prosthetics

A new method for the optimization of multilevel multivariable mechanical systems is presented. The method uses finite automata theory and algorithms for optimal control. The application of the algorithmic method to the optimal control of artificial human extremities is described.     

The influence of heat treatment and finishing on the mechanical and dielectric properties of glass fabric-epoxy resin laminar composites

The aim of this investigation was to define the optimum conditions of obtaining glass fabric-epoxy resin laminar composites with mechanical and dielectric properties that satisfy the quality needed for production of printed circuit boards for microelectronics. Commercial materials: glass woven fabric, different types of silane finish and epoxy resin were the starting materials in obtaining composites. The conditions needed for the thermal removal of the original size from glass fabric were investigated. The optimal heat treatment should be performed at temperatures less than 550 °C, while cooling rates should be as low as possible. In this manner, the fabric has less than 0.1% of residual size, and the mechanical properties remain satisfactory. Different types of adhesion promoters based on silanes were applied on heat-treated glass fabric as finishes. The quality of the composite material made of thermally and chemically treated glass fabric and epoxy resin was controled by measuring the tensile and dielectric strength of the composite. Depending on which properties of composite are of primary concern, mechanical or dielectric, a finish with an amino functional group and lower heat-treatment temperature or epoxy-modified coatings and higher heat-treatment temperature should be used for obtaining glass-fabric epoxy resin laminar composites.     

Hydrogen evolution on platinum in the presence of lead,cadmium and thallium adatoms

Hydrogen evolution on rotating platinum electrode has been measured in the presence of Pb, Tl and Cd adatoms. At low coverages of these adatoms (θ_M < 0.5) the mechanism of H₂ evolution is the same as that for Pt, giving rise to the Tafel slope of 30 mV with recombination of H adatoms as a rate controlling step. However, H₂ evolution decreases with θ_M to the fourth power, due to a simple blocking of Pt surface and a decrease of number of pairs of Pt atoms necessary for a recombination reaction. At higher coverages of foreign metal adatoms (θ_M ? 0.5), when the activation energy for the recombination of H adatoms becomes too high, the ion-plus atom reaction begins to control the rate of reaction. The Tafel slope acquires a value of 120 mV. Now, a decrease of H₂ evolution has been found proportional to the coverage of metal adatoms. A quantitative analysis based on above model agrees very well with the experiment. Some information on underpotential deposition of above metal on Pt has also been obtained.     

Application priority mathematical model of operating parameters in advanced manufacturing technology

The present work is devoted to the geometric calculation of shape parameters of the working surfaces of disk-shaver teeth for use in finishing cylindrical gears with an evolvent profile. These are primarily gears for the transmissions of cars and light trucks, which must meet strict noise requirements. This imposes corresponding requirements on their machining precision.     

Highly enhanced electrocatalytic oxygen reduction performance observed in bimetallic palladium-based nanowires prepared under ambient, surfactantless conditions

We have employed an ambient, template-based technique that is simple, efficient, and surfactantless to generate a series of bimetallic Pd(1-x)Au(x) and Pd(1-x)Pt(x) nanowires with control over composition and size. Our as-prepared nanowires maintain significantly enhanced activity toward oxygen reduction as compared with commercial Pt nanoparticles and other 1D nanostructures, as a result of their homogeneous alloyed structure. Specifically, Pd(9)Au and Pd(4)Pt nanowires possess oxygen reduction reaction (ORR) activities of 0.49 and 0.79 mA/cm(2), respectively, which are larger than the analogous value for commercial Pt nanoparticles (0.21 mA/cm(2)). In addition, core-shell Pt~Pd(9)Au nanowires have been prepared by electrodepositing a Pt monolayer shell and the corresponding specific, platinum mass, and platinum group metal mass activities were found to be 0.95 mA/cm(2), 2.08 A/mg(Pt), and 0.16 A/mg(PGM), respectively. The increased activity and catalytic performance is accompanied by improved durability toward ORR.     

The influence of vanadium on fracture toughness and abrasion resistance in high chromium white cast irons

The influence of vanadium on wear resistance under low-stress conditions and on the dynamic fracture toughness of high chromium white cast iron was examined in both the ascast condition and after heat treatment at 500 °C. A vanadium content varying from 0.12 to 4.73% was added to a basic Fe-C-Cr alloy containing 2.9 or 19% Cr. By increasing the content of vanadium in the alloy, the structure became finer, i.e. the spacing between austenite dendrite arms and the size of massive M₇C₃ carbides was reduced. The distance between carbide particles was also reduced, while the volume fraction of eutectic M₇C₃ and V₆C₅ carbides increased. The morphology of eutectic colonies also changed. In addition, the amount of very fine M₂₃C₆ carbide particles precipitated in austenite and the degree of martensitic transformation depended on the content of vanadium in the alloy. Because this strong carbide-forming element changed the microstructure characteristics of high chromium white iron, it was expected to influence wear resistance and fracture toughness. By adding 1.19% vanadium, toughness was expected to improve by approximately 20% and wear resistance by 10%. The higher fracture toughness was attributed to strain-induced strengthening during fracture, and thereby an additional increment of energy, since very fine secondary carbide particles were present in a mainly austenitic matrix. An Fe-C-Cr-V alloy containing 3.28% V showed the highest abrasion resistance, 27% higher than a basic Fe-C-Cr alloy. A higher carbide phase volume fraction, a finer and more uniform structure, a smaller distance between M₇C₃ carbide particles and a change in the morphology of eutectic colonies were primarily responsible for improving wear resistance.     

Enhanced Oxygen Reduction Activity of IrCu Core Platinum Monolayer Shell Nano-electrocatalysts

Designing novel cathode materials for a proton exchange membrane fuel cell with high activity for the oxygen reduction reaction, low Pt loading, and enhanced long-term stability is imperative for its sustainability. To date, Pt monolayer based electrocatalysts deposited on a metallic core substrate have shown promising possibilities. In this study, we synthesized bimetallic IrCu nanoparticles and used them as a core for Pt monolayer electrocatalysts. It was found that the de-alloyed IrCu nanoparticle surfaces increased both the mass and specific activities of the resulting Pt monolayer catalyst. In addition, we demonstrated that Pt monolayer electrocatalysts with a de-alloyed IrCu core have a better stability than those using a non-dealloyed core based on a 5,000 potential cycling test. These data describe a new simple synthesis of a high-performance catalyst suitable for practical applications.     

Evaluation of the phytomass source for composite preparation

The properties of lignocellulose materials from the trunk and bark of trees, and from agricultural sources were investigated by thermogravimetry (TG) and pyrolysis–gas chromatography/mass spectrometry (Py‐GC/MS). The goal was to learn which of the phytomass sources is the most accessible to dehydration and aldol reactions, and in this way could be considered suitable for composite preparation by the thermal pressing treatment. The bagasse second differential thermal analysis peak in air is at the highest temperature acceptable for intermolecular dehydration/crosslinking, and therefore we consider bagasse to be the most suitable candidate for composite preparation. From the TG results in air at 250°C, it follows that willow wood and bagasse are the most thermally resistant sources. The data obtained by Py‐GC/MS analysis showed glycolaldehyde and acetic acid as dominant markers related to adhesion properties via aldol condensation. The detected sum amount of glyceraldehyde and acetic acid decreases in the order: beech wood > bagasse > acacia wood > sugar beet pulp, whereas the remaining species produced much less of it. By comparing results run at above conditions with composite preparation using the pressing thermal treatment at a temperature of 150°C and pressures up to 800 kPa, the suggested evaluation was examined for application on sugar beet residue. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013