Poly(ethylene oxide)/clay nanocomposite: Thermomechanical properties and morphology

Poly(ethylene oxide) (PEO)/clay nanocomposites were prepared by a solution intercalation method using chloroform as a solvent. The nanocomposites were characterised by X-ray diffraction (XRD), differential scanning calorimetry (DSC), hot-stage polarized optical microscopy (POM), Fourier transform infrared spectroscopy (FT-IR), tensile analysis, dynamic mechanical analysis (DMA) characterisation techniques. Formation of nanocomposite was confirmed by X-ray diffraction (XRD) analysis. A decrease in PEO crystallinity in case of nanocomposite, was confirmed by a decrease in the heat of melting and spherulite size as indicated by DSC and POM studies, respectively. Improvement in tensile properties in all respect was observed for nanocomposites with optimum clay content (12.5 wt%). DMA studies indicate an increase in loss peak temperature and broadening of loss peak as a result of clay intercalation.     

Machining Characteristics and Corrosion Behavior of Grain Refined AZ91 Mg Alloy Produced by Friction Stir Processing: Role of Tool Pin Profile

In the present study, influence of friction stir processing (FSP) tool pin profile on the microstructure evolution, corrosion and machining characteristics of the AZ91 magnesium alloy was investigated. Three different pin profiles namely simple taper, threaded taper and square taper were selected and FSP was carried out at 1400 rpm and 25 mm/min tool travel speed. Microstructural observations indicated grain refinement from a starting grain size of 166.5–7.9, 22.1 and 4.08 µm for FSPed samples processed by simple taper, threaded taper and square taper pins, respectively. In all the FSPed samples, decreased amount of secondary phase (Mg₁₇Al₁₂) was observed compared with that of the unprocessed sample. From the X-ray diffraction analysis, it was observed that the square taper pin tool had induced higher texture effect compared with the other two FSP tools. From the electrochemical studies, the corrosion resistance of the sample processed with square taper pin tool was observed to be more in comparison to that of the other samples; which could be attributed to the texture effect and decreased fraction of secondary phase. Machining behavior assessed by conducting drilling experiments showed a significant influence of grain refinement on the cutting forces.     

A conceptual spacecraft radioisotope thermoelectric and heating unit (RTHU)

Spacecraft venturing to the outer planets and beyond—or onto the planetary surface where available solar energy is reduced—benefit from the longevity and consistency of electrical and thermal energy derived from radioisotope energy sources. A review of likely mission requirements and concept studies of small electrical generating units (<10 W_e) reveals a potential opportunity for a unit with an electrical output of around 1 W_e that can also supply some heat to the spacecraft to aid thermal control: a radioisotope thermoelectric and heating unit. This power requirement cannot be achieved with current US space‐qualified modular radioisotope fuel assemblies. Additionally, new European programmes consider ²⁴¹Am fuel to be much more cost effective than ²³⁸Pu. Taken together, these factors provide the rationale for taking a relatively ‘clean‐sheet’ approach to design of a radioisotope thermoelectric and heating unit fuelled with ²⁴¹Am. In this paper, initial requirements and performance targets for such a unit are developed, a simple concept design and thermal model is presented and the performance and mass are estimated. The results suggest that units generating 1–2 W_e may achieve a specific power of around 0.7–0.9 W_e kg^?1 without the thermal inputs to spacecraft becoming impractically large. Such units can use a bismuth telluride thermoelectric material, which is commercially applied in terrestrial applications and is therefore likely to incur lower cost and development risk than more specialised compounds. This study may form the basis of a more detailed design effort. Copyright © 2011 John Wiley & Sons, Ltd.     

Attribute-based key-insulated signature for boolean formula

In order to minimize the impact of secret signing key exposure in attribute-based signature scenario, we construct an attribute-based key-insulated signature (ABKIS) scheme for expressive monotone boolean function access structures utilizing only four pairing operations in verification process and making the signature length constant, that is, the number of pairings required for signature verification and the size of signature are independent of the size of attribute set participated in the respective process. The (strong) key-insulated selective security of our ABKIS scheme is reduced to the computational Diffie–Hellman Exponent problem without using any random oracles. The proposed construction attains signer privacy, which is a fundamental requirement of the signature schemes in the attribute-based setting.     

Morphology‐dependent electrocatalytic activity of nanostructured Pt/C particles from hybrid aerosol–colloid process

An optimum nanostructure and pore size of catalyst supports is very important in achieving high catalytic performances. In this instance, we evaluated the effects of various carbon nanostructures on the catalytic performances of carbon‐supported platinum (Pt/C) electrocatalysts experimentally and numerically. The Pt/C catalysts were prepared using a hybrid method involving the preparation of dense, hollow, and porous nanostructured carbon particle via aerosol spray pyrolysis followed by microwave‐assisted Pt deposition. Electrochemical characterization of the catalysts showed that the porous Pt/C catalyst gave the best performance; its electrochemical surface area was much higher, more than twice than those of hollow or dense Pt/C. The effects of pore size on electrocatalysis were also studied. The results showed the importance of a balance between mesopores and macropores for effective catalysis with a high charge transfer rate. A fluid flow model showed that good oxygen transport contributed to the catalytic activity. © 2015 American Institute of Chemical Engineers AIChE J, 62: 440–450, 2016     

Polyethylene nanocomposites by gas‐phase polymerization of ethylene in the presence of a nanosilica‐supported zirconocene catalyst system

BACKGROUND: Much of the current research related to the development of in situ nanocomposites of olefins by polymerizing them with metallocenes in the presence of surface‐treated fillers is carried out in the slurry phase. In slurry‐phase methods a large amount of solvent is required and there is always a need of purification of the final product due to the possibility of traces of solvents present in the product. To overcome these drawbacks, to perform solvent‐free metallocene‐catalysed polymerizations with in situ incorporation of inorganic nanoparticles, we have used a gas‐phase polymerization technique as this does not require solvents and also utilizes monomer feed stocks efficiently. RESULTS: The catalyst used for the synthesis of in situ polyethylene nanocomposites by gas‐phase polymerization was nanosilica‐supported zirconocene. The fillers used were Cloisite‐20A, kaolin and nanosilica. Three different in situ polyethylene nanocomposites, i.e. Cloisite‐20A‐filled polyethylene (CFPE), kaolin‐filled polyethylene (KFPE) and nanosilica‐filled polyethylene (SFPE), were prepared by gas‐phase polymerization. The nanocomposites were obtained in the form of fine powder. The polyethylene content in the developed nanocomposites is in the orthorhombic crystalline phase. Using our approach, it is observed that the nanofillers are completely encapsulated by a thin layer of polyethylene. Significantly higher molecular weight polyethylene was formed in the case of KFPE in comparison to CFPE and SFPE. The thermal decomposition temperature, melting temperature and enthalpy are also observed to be higher for KFPE. CONCLUSIONS: The gas‐phase polymerization technique has been successfully carried out for the synthesis of in situ polyethylene nanocomposites. Copyright © 2007 Society of Chemical Industry     

Development of controlled strength-loss resorbable beta-tricalcium phosphate bioceramic structures

Controlling the strength-loss rate during biodegradation is a bottleneck in developing viable resorbable ceramic implants. Resorbable beta-tricalcium phosphate (β-TCP) bioceramic is known for its excellent biocompatibility. However, it exhibits poor sinterability and poor flexural strength. Here, we improved sintering behavior and biaxial flexural strength of β-TCP bioceramic without altering its biocompatibility by introducing multi-oxide sintering additives, in small quantities. These additives could also tailor the rate of resorption and hardness deterioration of β-TCP. A range of additives were prepared and introduced into β-TCP powder. Resultant powders were uniaxially pressed and sintered at 1250 °C, in air. Considerable improvement in densification (up to 33%) and biaxial flexural strength (up to 43%) were achieved. X-ray powder diffraction (XRD) analysis confirmed that the additives didn't alter the phase purity. In vitro cytotoxicity and biocompatibility analyses were performed using a prostate cancer cell-line. Results showed that the doped and pure β-TCP structures were non-toxic and biocompatible.     

Effect of modified layered silicates on the confined crystalline morphology and thermomechanical properties of poly(ethylene oxide) nanocomposites

In this work, poly(ethylene oxide) (PEO)/organoclay nanocomposites with three different types of nanoclays (Cloisite 30B, Somasif JAD400, and Somasif JAD230) were prepared by melt mixing with a laboratory kneader followed by compression molding. The nanocomposites were characterized by atomic force microscopy and scanning electron microscopy. Their crystallization behavior on a hot stage was investigated with polarized optical microscopy. The size and regularity of the spherulites of the PEO matrix were altered significantly by the incorporation of Cloisite 30B, but there was not as much variation with the other two clays. The dynamic viscoelastic behavior of the PEO/organoclay nanocomposites was assessed with a strain‐controlled parallel‐plate rheometer. The effects of clay modification on the thermomechanical and rheological properties were addressed. The reinforcing effect of the organoclay was determined with dynamic mechanical analysis and tensile testing. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Interactions of Polyacrylamide with Cationic Surfactants: Thermodynamic and Surface Parameters

The aggregation behaviour of two cationic surfactants, viz. cetyl trimethyl ammonium bromide (CTAB) and N-cetyl pyridinium chloride (CPC), in different concentrations of water-soluble polyacrylamide has been studied in alkaline medium by electrical conductivity and surface tension measurements. A decrease in the critical micelle concentration (CMC) of the surfactant with an increase in polymer content in the mixture was observed. The thermodynamic and surface parameters have been determined and discussed. The results indicate that micellisation becomes more favourable at higher polymer content.     

Graphical fault tree analysis for fatal falls in the construction industry

The current study applied a fault tree analysis to represent the causal relationships among events and causes that contributed to fatal falls in the construction industry. Four hundred and eleven work-related fatalities in the Taiwanese construction industry were analyzed in terms of age, gender, experience, falling site, falling height, company size, and the causes for each fatality. Given that most fatal accidents involve multiple events, the current study coded up to a maximum of three causes for each fall fatality. After the Boolean algebra and minimal cut set analyses, accident causes associated with each falling site can be presented as a fault tree to provide an overview of the basic causes, which could trigger fall fatalities in the construction industry. Graphical icons were designed for each falling site along with the associated accident causes to illustrate the fault tree in a graphical manner. A graphical fault tree can improve inter-disciplinary discussion of risk management and the communication of accident causation to first line supervisors.