Investigation of wax deposit ‘sloughing’ from paraffinic mixtures in pipe flow

Deposit ‘sloughing’ from ‘waxy’ crude oils has been described in the literature as a possible mechanism, leading to partial or complete dislodging of the deposit from the pipe wall due to changes in flow parameters. A bench‐scale flow loop apparatus was used to investigate ‘sloughing’ with prepared single‐phase ‘waxy’ mixtures of a multicomponent paraffinic wax dissolved in a multicomponent solvent. Experiments were performed to study the changes in the deposit‐layer thickness due to step increments in the ‘waxy’ mixture flow rate, the mixture temperature, and the coolant temperature. It was observed that the deposit‐layer thickness decreased with an increase in each of the three parameters; however, a complete or sudden dislodging of the deposit‐layer did not occur in any of the experiments. A steady‐state heat‐transfer model was used to predict the variation in the deposit mass or thickness due to changes in the selected parameters. In each case, the step‐wise decrease in the deposit thickness, as observed experimentally, was predicted to be caused by changes in the thermal resistance and/or thermal driving force.     

High resolution quantitative piezoresponse force microscopy of BiFeO3 nanofibers with dramatically enhanced sensitivity

Piezoresponse force microscopy (PFM) has emerged as the tool of choice for characterizing piezoelectricity and ferroelectricity of low-dimensional nanostructures, yet quantitative analysis of such low-dimensional ferroelectrics is extremely challenging. In this communication, we report a dual frequency resonance tracking technique to probe nanocrystalline BiFeO(3) nanofibers with substantially enhanced piezoresponse sensitivity, while simultaneously determining its piezoelectric coefficient quantitatively and correlating quality factor mappings with dissipative domain switching processes. This technique can be applied to probe the piezoelectricity and ferroelectricity of a wide range of low-dimensional nanostructures or materials with extremely small piezoelectric effects.     

Three-dimensional microstructural changes in the Ni–YSZ solid oxide fuel cell anode during operation

Microstructural evolution in solid oxide fuel cell (SOFC) cermet anodes has been investigated using X-ray nanotomography along with differential absorption imaging. SOFC anode supports composed of Ni and yttria-stabilized zirconia (YSZ) were subjected to extended operation and selected regions were imaged using a transmission X-ray microscope. X-ray nanotomography provides unique insight into microstructure changes of all three phases (Ni, YSZ, pore) in three spatial dimensions, and its relation to performance degradation. Statistically significant 3D microstructural changes were observed in the anode Ni phase over a range of operational times, including phase size growth and changes in connectivity, interfacial contact area and contiguous triple-phase boundary length. These observations support microstructural evolution correlated to SOFC performance. We find that Ni coarsening is driven by particle curvature as indicated by the dihedral angles between the Ni, YSZ and pore phases, and hypothesize that growth occurs primarily by means of diffusion and particle agglomeration constrained by a pinning mechanism related to the YSZ phase. The decrease in Ni phase size after extended periods of time may be the result of a second process connected to a mobility-induced decrease in the YSZ phase size or non-uniform curvature resulting in a net decrease in Ni phase size.     

Antibacterial Activity of the Sponge Ircinia Ramosa: Importance of its Surface-Associated Bacteria

Variations in the antibacterial activity of the sponge Ircinia ramosa were evaluated during two collection periods (January and May) against vicinity fouling bacteria (VFB) and sponge surface-associated bacteria (SAB). The density of fouling bacteria in the water column, as well as epibacterial abundance on the sponge surface, was enumerated during both collections, and both increased in the warmer month of May. The extracts obtained from SAB were also tested for their role in antibacterial activity of the host. Sponge-associated bacteria are capable of producing antibacterial metabolites. The antibacterial activity that originated from polar fractions in the cooler month of January shifted towards the nonpolar fractions in May. Nonpolar fractions were more useful for the sponge when threatened with increased bacterial density. Thus, the chemical nature and production of antibacterial compounds produced by sponge or its associated bacteria appears to be governed by the environment. An inverse relationship was observed between the epibacterial abundance over the sponge surface in nature and the antibacterial activity displayed by the sponge extracts in laboratory bioassays. This investigation reveals the importance of collection period as well as the role of associated bacteria in the evaluation of antibacterial activity.     

Effect of dynamic cross‐linking on melt rheological properties of polypropylene/ethylene‐propylene‐diene rubber blends

Study of melts rheological properties of unvulcanized and dynamically vulcanized polypropylene (PP)/ethylene‐propylene‐diene rubber (EPDM) blends, at blending ratios 10–40 wt %, EPDM, are reported. Blends were prepared by melt mixing in an internal mixer at 190°C and rheological parameters have been evaluated at 220°C by single screw capillary rheometer. Vulcanization was performed with dimethylol phenolic resin. The effects of (i) blend composition; (ii) shear rate or shear stress on melt viscosity; (iii) shear sensitivity and flow characteristics at processing shear; (iv) melt elasticity of the extrudate; and (v) dynamic cross‐linking effect on the processing characteristics of the blends were studied. The melt viscosity increases with increasing EPDM concentration and decreased with increasing intensity of the shear mixing for all compositions. In comparison to the unvulcanized blends, dynamically vulcanized blends display highly pseudoplastic behavior provides unique processing characteristics that enable to perform well in both injection molding and extusion. The high viscosity at low shear rate provides the integrity of the extrudate during extrusion, and the low viscosity at high shear rate enables low injection pressure and less injection time. The low die‐swell characteristics of vulcanizate blends also give high precision for dimensional control during extrusion. The property differences for vulcanizate blends have also been explained in the light of differences in the morphology developed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1488–1505, 2000     

Effect of dynamic crosslinking on tensile yield behavior of polypropylene/ethylene‐propylene‐diene rubber blends

Tensile yield behavior of the blends of polypropylene (PP) with ethylene‐propylene‐diene rubber (EPDM) is studied in blend composition range 0–40 wt % EPDM rubber. These blends were prepared in a laboratory internal mixer by simultaneous blending and dynamic vulcanization. Vulcanization was performed with dimethylol phenolic resin. For comparison, unvulcanized PP/EPDM blends were also prepared. In comparison to the unvulcanized blends, dynamically vulcanized blends showed higher yield stress and modulus. The increase of interfacial adhesion caused by production of three‐dimensional network is considered to be the most important factor in the improvement. It permits the interaction of the stress concentrate zone developed at the rubber particles and causes shear yielding of the PP matrix. Systematic changes with varying blend composition were found in stress‐strain behavior in the yield region, viz., in yield stress, yield strain, width of yield peak, and work of yield. Analysis of yield stress data on the basis of the various expressions of first power and two‐thirds power laws of blend compositions dependence and the porosity model led to consistent results from all expression about the variation of stress concentration effect in both unvulcanized and vulcanized blend systems. Shapes and sizes of dispersed rubber phase (EPDM) domains at various blend compositions were studied by scanning electron microscopy. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2104–2121, 2000     

Thermodynamic and Kinetic Effects of Oxygen Removal on the Thermal Conductivity of Aluminum Nitride

High thermal conductivity, low dielectric constant, high electrical resistivity, low density, and a thermal expansion coefficient that matches well with that of silicon are the principal attributes of AIN that have attracted much attention over the past decade. It is also now well established that oxygen as an impurity lowers the thermal conductivity of AIN. Processing techniques have been developed which not only facilitate pressureless densification of AIN but also enhance its thermal conductivity. The present work explores the thermodynamics and the kinetics of oxygen removal and the resultant enhancement of thermal conductivity. Polycrystalline AIN ceramics were fabricated with Y₂O₃, Dy₂O₃, Yb₂O₃, CaO, BaO, or MgO as additives. Samples were sinter/annealed at 1850°C for up to 1000 min. The AIN grain size of sintered samples ranged between 2 and 9 μm. The samples typically contained two or three phases with the predominant phase being AIN. Secondary phases in Y₂O₃-doped AIN consisted of yttrium aluminates which were along three grain junctions and along grain facets. The presence of Y₃Al₅O₁₂, YAIO₃, and Y₄Al₂O₉, as well as Y₂O₃, depending upon the Y₂O₃/Al₂O₃ ratio, was revealed by X-ray diffraction. Thermal conductivity increased with the amount of additive and annealing time. Thermal conductivity also depended on the type of additive. Samples with thermal conductivity up to 200 W/(m · K) were fabricated. The variation in thermal conductivity with the type and the amount of the additive is explained on the basis of the thermodynamics of oxygen removal. In particular, the higher thermal conductivity of CaO-doped, in comparison with MgO-doped, samples is rationalized on the basis that the free energy of formation, ΔG°, of CaAl₂O₄ is less than that of MgAl₂O₄. It is proposed that the higher the |ΔG°|, with ΔG° < 0, the higher is the resultant thermal conductivity. An increase in the thermal conductivity with annealing time is attributed to the kinetics of oxygen removal from AIN grains.     

Solution of mass transfer in step growth polymerization in films with bulk in equilibrium

We have analyzed step growth polymerization in a flat film with finite mass transfer resistance. We have shown rigorously that the molecular weight distribution (MWD) at equilibrium is given by the Flory distribution, and under reaction the form of the MWD does not change if the feed is either pure monomer or in equilibrium initially. Extensive computations have shown that it is possible to split the film into growing interfacial and shrinking bulk regions. It is possible to obtain similarity transformations of concentrations of condensation product, and polymer as time invariant profiles. Based on this finding, we have determined a solution for step growth polymerization with finite mass transfer in films. The results lie within 5% of the “exact” numerical computations, for all possible variations of parameters.     

Influence of Mg Addition on the Catalytic Activity of Alumina Supported Ag for C3H6-SCR of NO

The influence of different magnesium (Mg) weight percentages (1, 2.5, 5, 7.5 and 10) over silver (3 wt%) impregnated alumina (SA) catalyst was investigated for the reduction of NO by C₃H₆. Mg doped SA catalysts were prepared by conventional impregnation method and characterized by XRD, BET-SA, ICP-MS, XPS, SEM, UV-DRS, H₂-TPR and O₂-TPD. The existence of MgO and MgAl₂O₄ phases on Mg doped SA catalysts were observed from XRD and XPS analyses. Existence of high percentage MgAl₂O₄ phase on 5% Mg doped SA catalyst (Mg (5) SA) enhances the dispersion and stabilization of silver phases (Ag₂O). Mg (5) SA catalyst shows a 51% of high selectivity (NO to N₂) in presence of SO₂ (80 ppm) at low temperatures (350 °C) and maintained high selectivity’s with a wide temperature window (350–500 °C). An optimal high surface availability of Ag⁰ and Ag⁺ species were observed from XPS analysis over Mg (5) SA catalyst. H₂-TPR analysis shows high temperature reduction peak over Mg (5) SA compared to SA catalyst. XPS analysis confirms the high percent availability of MgAl₂O₄ species over Mg (5) SA catalyst. DRIFTS study reveals the molecular evidences for the evolution of enolic species during NO reduction over the highly active Mg (5) SA catalyst at low temperatures. It also confirms further transformation of enolic species into –NCO species with NO + O₂ and finally into N₂ and CO₂.     

Influence of carbon‐based nanofillers on the electrical and dielectric properties of ethylene vinyl acetate nanocomposites

A comparative study of ethylene vinyl acetate nanocomposites based on expanded graphite, multiwalled carbon nanotubes, and carbon nanofibers has been carried out to investigate the effect of different carbon nanofillers on the electrical properties of the corresponding composites. The composites were prepared by ultrasonic dispersion of fillers in ethylene vinyl acetate solution, followed by casting and compression molding. The dependence of AC conductivity and dielectric constant on the frequency and filler concentration was investigated. Carbon nanofibers provided maximum conductivity as well as lowest percolation threshold (8.2 vol%) compared to expanded graphite and multiwalled carbon nanotubes filled composites. The improvement in both electrical conductivity and dielectric constant was attributed to the high filler aspect ratio and the formation of conducting networks. The relationship of dielectric constant with filler volume fraction for all the composite systems is estimated using a power law. The pressure sensing capability of the composites at respective percolation thresholds was also compared. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers