High temperature bending creep behavior of a multi-cation doped α/β-SiAlON composite

SiAlON ceramics with high hardness and high toughness can be made through designing α/β-SiAlON composites. An important advantage of α-SiAlON phase is that the amount of intergranular phase is reduced by the transient liquid phase being absorbed into the matrix of α-SiAlON phase during sintering. But, the thermal stability of the α-SiAlON phase is an important concern for α/β-SiAlON composites especially at high temperatures. The use of different types of single or multiple cations during fabrication directly affects resultant microstructures and mechanical behavior of α/β-SiAlON composites. In this study, the creep behavior of a multi-cation (Y, Sm and Ca) doped α/β-SiAlON composite, in which aluminum-containing nitrogen melilite solid solution phase was designed as intergranular phase, was investigated by four-point bending creep tests under stresses from 50 to 150 MPa and at temperatures from 1300 °C to 1400 °C in air. The stress exponent was determined to be 1.6 ± 0.13 at 1400 °C and the creep activation energy was calculated to be 692 ± 37 kJ/mol⁻¹. Grain boundary sliding coupled with diffusion was identified as the rate-controlling creep mechanism for the α/β-SiAlON composite.     

Polyamide 6–Cellulose Composites: Effect of Cellulose Composition on Melt Rheology and Crystallization Behavior

Melt rheology and crystallization behavior of polyamide 6 (PA 6) and microcrystalline cellulose (MCC) composites were systematically studied in this research. The incorporation of MCC into the PA 6 matrix resulted in higher complex viscosities (|η*|), storage modulus (G′), and shear viscosities than those of neat PA 6, especially at low frequencies. The orientation of rigid molecular chains in the composites introduced by the addition of MCC induced a strong shear thinning behavior with an increase in MCC loading. The non‐isothermal crystallization kinetics of PA 6 and MCC composites were investigated by differential scanning calorimetry. The Avrami and Tobin model were applied to describe the process of non‐isothermal crystallization and to determine the crystallization parameters of the composites. Analysis of the crystallization kinetics indicated that the Avrami (n_a) and Tobin exponent (n_t) was altered by the MCC. It was also found that the Avrami and Tobin equations fit the empirical data well. POLYM. ENG. SCI., 54:739–746, 2014. © 2013 Society of Plastics Engineers     

Reaction Mechanism and Kinetics of 1,8‐Diazabicyclo[5.4.0]undec‐7‐ene and Carbon Dioxide in Alkanol Solutions

Carbon dioxide‐binding organic liquids (CO₂BOL) are a new class of solvents with advantageous properties such as high boiling points, low specific heats, high absorption capacities, and easily reversible reactions. In order to implement these solvents in processes, the reaction characteristics must be determined a priori. This work presents an analysis of the rate constants and activation energies of the reaction between carbon dioxide and 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) in 1‐hexanol and 1‐propanol. The reactions were found to comply with a termolecular reaction mechanism and exhibited pseudo‐first‐order behavior in the presence of excess DBU and 1‐alkanol. It was concluded that DBU‐based CO₂BOL are environmentally friendly and easy‐to‐handle solvents that may provide great flexibility and improvements over conventional carbon dioxide absorption processes.     

Thermal energy storage by poly(styrene-co-p-stearoylstyrene) copolymers produced by the modification of polystyrene

A series of poly(styrene-co-p-stearoyl styrene) copolymers as novel polymeric solid–solid phase-change materials (SSPCMs) were synthesized by the modification of polystyrene with stearoyl chloride. The chemical structure and crystalline morphology of the synthesized copolymers were determined with Fourier transform infrared spectroscopy and polarized optical microscopy, respectively. The thermal energy storage properties and thermal stability of the SSPCMs were investigated with differential scanning calorimetry and thermogravimetric analysis, respectively. In addition, the thermal conductivity of the SSPCMs was measured with a thermal property analyzer. Moreover, thermal cycling tests showed that the copolymers had good thermal reliability and chemical stability after being subjected to 5000 heating/cooling cycles. The synthesized poly(styrene-co-stearoyl styrene) copolymers as novel SSPCMs have considerable potential for thermal energy storage and temperature-control applications. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of processing method on microstructure,electrical conductivity and electromagnetic wave interference (EMI) shielding performance of carbon nanofiber filled thermoplastic polyurethane composites

In this study, effect of processing method on microstructure formation and related electrical conductivity and electromagnetic interference shielding effectiveness of carbon nanofiber (CNF) filled thermoplastic polyurethane (TPU) composites, prepared via three different processing techniques; (i) melt compounding (MC) in a twin screw extruder, (ii) simple solution mixing (SM) on a magnetic stirrer, and (iii) solution mixing with sonication (SM-U) were investigated. It was found that the electrical conductivity values of samples decreased in the order of SM > SM-U > MC for a particular amount of CNF. The electromagnetic test results showed that the samples prepared with SM and SM-U methods yielded higher total shielding effectiveness (SE_T) values than those prepared with MC. SE_T values of samples including of 20 phr of CNF prepared with MC, SM-U and SM methods were varied in the range of 10–30 dB, 20–60 dB and 20–80 dB, respectively within a frequency range of 1–12 GHz.     

CHARACTERIZATION OF CERIUM OXIDE AND CARBON SUPPORTED Ag-Cu ELECTRO-CATALYSTS FOR ANODE ELECTRODE IN DIRECT ETHANOL FUEL CELLS

In this study, electrochemical and spectroscopic characterization of home-made CeO₂, activated carbon-based Ag-Cu electro-catalysts, and preliminary anode polarization results in a direct ethanol fuel cell test system were presented. Ag-Cu transition metal couples were impregnated onto carbon and cerium oxide supports by wet impregnation, ion exchange, and co-precipitation techniques. Wet impregnation technique was selected for further spectroscopic analysis and fuel cell testing due to its easy metal loading advantage and highest peak currents in ethanol-containing electrolyte environment. When Ag and Cu were loaded 37.5 and 12.5 wt.% onto carbon and cerium oxide by wet impregnation technique, XPS analysis indicated an appreciable amount of Ag and Ag₂O and a high amount of CuO. In cerium oxide-based samples atomic percentage of oxygen fits well with the stoichiometry of CuO/CeO₂. Preliminary results show that BET surface area and the current peaks exhibit a close resemblance (highest BET surface area indicates highest anodic dissolution current), which is thought to be due to the high accessibility of copper layers impregnated onto cerium oxide and activated carbon in H₂SO₄ electrolyte environment. Hydrogen reduction of CeO₂-based samples prepared by wet impregnation at 750°C greatly improved anode polarization and onset oxidation potential.     

Effect of conductive layer on the performance of gel electrolyte-based supercapacitors

Solid-state electrolytes such a further novel finding is going to have great importance because of the disadvantages of liquid electrolytes such as electrochemical instability, low ion selectivity, and interface contact. It is anticipated that the use of solid-state electrolytes including supercapacitors (SCs) will become widespread with decreasing self-leakage and environmental damage more than liquid electrolytes. In this study, SCs with graphene/PEDOT: PSS coated electrodes and binary PVA gel electrolytes with a conductive layer were designed and the electrochemical performance of the configurations was characterized. The effects of the conductive layer between binary electrolytes and the concentration of the KOH solution in the electrolytes were studied. It was observed that the conductive layer used between the gel electrolytes causes additional charging at the electrolyte/conductive layer interface and behaves like a serially connected capacitor to the double-layer capacitor. Interestingly, at a slow sweep rate (5 mV/s), the specific capacitance values of the assembled SCs decreased when a conductive layer was used but it increased when the sweep rate was fast (100 mV/s).     

Rhodium Complexed C2‐PAMAM Dendrimers Supported on Large Pore Davisil Silica as Catalysts for the Hydroformylation of Olefins

Polyamidoamine (PAMAM) dendrimers up to the third generation were grown for the first time on the surface of a large‐pore (18 nm) Davisil silica support. The supported dendrimers of generations 0, 1, 2 and 3 were phosphinomethylated and complexed with rhodium. All the generations were found to be very active for the hydroformylation of olefins. The hydroformylation of 1‐octene was accomplished with a turnover frequency of 1700 h⁻¹ at 70 °C. The G(1) material was found to be the most active when the different generations were compared at 50% conversion at 70 °C     

Effect of a Small Amount of Synthetic Fiber on Performance of Biocarbon-Filled Nylon-Based Hybrid Biocomposites

Advanced hybrid biocomposites are engineered from nylon 6, waste wood biosourced carbon (biocarbon) with a low content of synthetic fiber for lightweight auto-parts uses. The novel engineering process through direct injection molding of only 2 wt% synthetic fibers in the form of masterbatch with 20 wt% biocarbon, results outstanding performance of the resulting nylon biocomposites. Such uniquely developed biocomposites show tensile strength of 105 MPa and tensile modulus of 5.14 GPa with a remarkable heat deflection temperature (HDT) of 206 °C. The direct injection molding of synthetic fiber retains the length ≈3 times higher as compared to traditional extrusion and injection molding; resulting greater degree of entanglement and composite reinforcement effectiveness in the hybrid biocomposites. Highly dimensionally stable nylon 6 biocomposites with a very low coefficient of linear thermal expansion results through reinforcing ability of the sustainable biocarbon and small amount of synthetic fiber.