Iridium-catalyzed aerobic oxidation of alkylarenes with excellent turnover numbers

A highly efficient catalyst system has been developed for the aerobic oxidation of alkylarenes under solvent free conditions. The combination of iridium complex, nitrogen ligand and iodobenzene was found to be crucial for catalytic activity. Excellent turnover numbers were achieved for the preparation of benzoic acids and aryl ketones. This finding may provide useful clues for improving commercially important oxidation processes.     

Air heat exchangers with long heat pipes: Experiments and predictions

This paper presents measurements and predictions of a heat pipe-equipped heat exchanger with two filling ratios of R134a, 19% and 59%. The length of the heat pipe, or rather thermosyphon, is long (1.5 m) as compared to its diameter (16 mm). The airflow rate varied from 0.4 to 2.0 kg/s. The temperatures at the evaporator side of the heat pipe varied from 40 to 70 °C and at the condenser part from 20 to 50 °C. The measured performance of the heat pipe has been compared with predictions of two pool boiling models and two filmwise condensation models. A good agreement is found. This study demonstrates that a heat pipe equipped heat exchanger is a good alternative for air–air exchangers in process conditions when air–water cooling is impossible, typically in warmer countries.     

Effect of plasticizer and storage conditions on thermomechanical properties of albumen/tragacanth based bioplastics

The effects of composition of the plasticizer fraction and storage conditions on the physical and thermomechanical properties of egg albumen/tragacanth gum based bioplastics were studied. Thus, glycerol (G) and water (W) were used as plasticizers at different G/W ratios (1:0, 3:1, 1:1, 1:3, 0:1), keeping the biopolymer fraction always at 60% (w/w). Tragacanth gum was included in the formulation for its well-known hydrophilic character, as possible future applications of these bioplastics may be moisture dependent (e.g. modified atmosphere packaging). Moreover, properties of bioplastics stored at room temperature under no control of relative humidity were different of those obtained when bioplastics were equilibrated a 53% relative humidity (RH) atmosphere. This is reflected in the DMTA and tensile tests results, for which water loss in the samples with the highest water contents (1:3, 0:1) involves very significant increases in viscoelastic moduli and tensile strength when equilibrated at 53% RH. Glycerol presence when no RH control was taken promotes water uptake, probably due to an interaction between both plasticizers, which eventually lead to a greater plastic region in the tensile tests.     

Healing behavior of a matrix crack on a carbon fiber/mendomer composite

The cure kinetics of a thermally mendable polymer based on Diels-Alder (DA) and retro-Diels-Alder (rDA) reactions, mendomer 401, was investigated using dynamic differential scanning calorimetry (DSC). The resulting behavior was modeled using a conventional cure kinetic model for thermosetting polymers. A composite panel with two layers of carbon fabric and mendomer 401 was fabricated following the cure cycle suggested by the cure kinetics model. Micro-indentation tests were performed to investigate mechanical properties and dynamic mechanical thermal analysis (DMTA) was conducted to study thermal behavior and to find the trigger temperature for healing. Self-healing behavior of the carbon fiber/mendomer composite was demonstrated using electrical resistive heating over the glass transition temperature.     

Functionalized nano diamond composites for photocatalytic hydrogen evolution and effective pollutant degradation

Development of superior heterogeneous photocatalyst for hydrogen (H₂) evolution with promising pollutant degradable capacity is a significant feature but then again thought-provoking for shaping the energy and environmental issues. In this regard, a photocatalytic H₂ evolution using nano diamond (ND) semiconducting materials having pollutant degradable capacity for Rhodamine B dye (RhB) has been rarely reported and hence predicted to the sustainable energy. Productive characteristics such good chemical stability, super hardness, nanometer size, biocompatibility and thermal conductivity, ND is a capable and highly valuable powder physical material. Non-uniform and agglomeration dispersion spread of ND in different solvents are the main problems preventing ND from the wide-use in commercial applications. Upon 535 nm solar light excitation, the fabricated ND sample exhibit remarkable photocatalytic H2 production with a HER of about 400 μmol h⁻¹ than pristine ND (197 μmol h⁻¹). Additionally, this H2 generation dramatically enhances the quantum yield, indicating the H2 terminated sites work as electron reservoirs. Precisely, the kinetic constant pseudo-order of FND for photodegradation of RhB was higher as compared with pristine ND. As such, the results show an important step toward tailor-designed and explain the vital role of FND composites for the rational motifs of fruitful photocatalyst with effective pollutant degradable capability for future demand.     

Morphology of rust phases formed on weathering steels in various laboratory corrosion tests

The morphology and growth characteristics of rust phases formed on ASTM A-588 weathering steel in three different types of laboratory tests—accelerated atmospheric exposure simulation tests (AAEST), salt fog test, and continuous immersion test in plain as well as salt water—are analyzed using microstructural information obtained from representative exposed specimens studied in a scanning electron microscope (SEM). The ultimate and most dominant phase in the AAEST was α-FeOOH whereas an amorphous phase designated as amorphous bulk (AB) appeared as “cotton bolls” in the adherent, sedimentary layer formed on the steel surface during continuous immersion. Crystalline phases α-, δ-, and γ-FeOOH as well as γ-Fe₂O₃.H₂O were found developed on top of the first-formed sedimentary amorphous layer, containing another amorphous phase designated as amorphous mix (AM). Magnetite was the dominant phase obtained in the salt fog test. It forms in layers and seems to transform to α-FeOOH through formation of whiskers and rods on its surface. Sandy grains of γ-Fe₂O₃.H₂O were also seen in the rusts obtained in this test.     

Identification of the internal forces of structural systems using feedforward multilayer networks

This paper explores the potential of using parallel distributed processing (neural network) approaches to identify the internal forces of typical systems encountered in the field of structural dynamics. Such problems arise in the context of structural control and the “health monitoring” of dynamic systems. After formulating the identification task as a neural network learning procedure, the method is applied to a representative example problem under a variety of excitations. The range of validity of the approach is demonstrated, and some application issues are discussed.     

Preparation and lithium-storage performance of carbon/silica composite with a unique porous bicontinuous nanostructure

A class of carbon/silica composite with a porous bicontinuous nanostructure is prepared via a simple sol–gel method and then used as anode material for lithium-ion batteries. The reversible specific capacity of the as-prepared composite stays over 560 mAh g⁻¹ after 30 cycles, much higher than that of many other carbon materials including commercial graphite and carbon/silica composites. The good electrochemical performance can be ascribed to the following three factors: (i) continuous silica gel framework stores most of lithium ions; (ii) continuous carbon framework not only restrains the volume change during repeated insertion and extraction of lithium ions, but also represents an excellent conductive skeleton throughout the composite; (iii) nanopores among the carbon/silica bicontinuous framework are helpful to the mass transport and can further buffer the volume change of silica.