Effect of Carbon Nanotube Dispersion on Mechanical Properties of Aluminum-Silicon Alloy Matrix Composites

This study has been carried out to reinforce the commonly believed fact that the dispersion of carbon nanotubes in a composite has a profound effect on the properties of the composite. In this study, ball milling was carried out using two different parameters to obtain distinctly different degrees of dispersion of carbon nanotubes (4 wt.%) in Al-9 wt.% Si powders. Composite disks, 80 mm in diameter, having good and bad dispersions of carbon nanotubes were obtained by hot pressing. Optical micrographs and Raman spectroscopy images showed the presence of larger carbon nanotube clusters in the bad dispersion sample. Transmission electron microscopy images confirmed the presence of large clusters in the bad dispersion sample, while the good dispersion sample showed individual carbon nanotubes in the Al matrix. Nanoindentation results indicated a 41% increase in the hardness and a 27% increase in the elastic-to-plastic work ratio, while compression tests indicated a 185% increase in compression yield strength and a 109% increase in fracture strength with improvement in carbon nanotube’s dispersion.     

(S)-2-(ethyl propionate)-(O-ethyl xanthate)- and (S)-2-(Ethyl isobutyrate)-(O-ethyl xanthate)-mediated RAFT polymerization of vinyl acetate

(S)-2-(Ethyl propionate)-(O-ethyl xanthate) (X1) and (S)-2-(Ethyl isobutyrate)-(O-ethyl xanthate) (X2) were used as the reversible addition-fragmentation chain transfer (RAFT) agents for the radical polymerization of vinyl acetate (VAc). The former showed the better chain transfer ability in the polymerization at 60°C. Kinetic study with both RAFT agents showed pseudo-first order kinetics up to around 85% monomer conversion. Molecular weight of the resulting polymer increased linearly with increase in the monomer conversion up to around 85%. The observed molecular weights calculated from ¹H-NMR spectrum [M_n(NMR)] are close to the corresponding theoretical molecular weights [M_n(theor)]. The corresponding polydispersity index (PDI) of the resulting polymers remained almost constant at around 1.2 up to ∼ 65% monomer conversion and then increased gradually with the further increase in the monomer conversion. Chain-end analysis of the resulting polymers by ¹H-NMR showed clearly that polymerization started with the radical forming out of the xanthate mediator. The negligible homo-chain extension and the hetero-chain extension involving synthesis of poly(VAc)-b-poly(NVP) diblock copolymer were occurred. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

High Temperature Corrosion Behavior of Cold Spray Ni-20Cr Coating on Boiler Steel in Molten Salt Environment at 900 °C

Cold spray is an emerging technology that produces high density metallic coatings with low oxide contents and high thermal conductivity, which makes them ideal for high temperature corrosion resistance. In the current investigation, Ni-20Cr alloy powder was deposited on SA 516 boiler steel (0.19C-1.07Mn-0.020S-0.25P-0.010Si-balance Fe) by cold spray process. Oxidation kinetics was established for the uncoated and cold spray Ni-20Cr coated boiler steel in an aggressive environment of Na₂SO₄-60%V₂O₅ at 900 °C for 50 cycles by the weight change technique. X-ray diffraction, FE-SEM/EDAX, and x-ray mapping techniques were used to analyze the oxidation products. Uncoated steel suffered corrosion in the form of intense spalling and peeling of its oxide scale, which may be due to the formation of unprotective Fe₂O₃ oxides. The Ni-20Cr coating was successful in reducing the weight gain of the steel by 87.2% which may be due to the formation of oxides of nickel and chromium.     

Group mobility by cooperative communication for high speed railway

Wireless Networks - The high speed railway (HSR) provides more convenience to people, so the main attention is given to provide the reliable communication inside the train. It is the challenging...     

Proposing ab initio assisted lattice distortion theory for phase equilibrium: Pure and mixed refrigerant gas hydrates

With promising applications in cold storage and seawater desalination, various refrigerant gas hydrates are experimentally studied for their phase equilibrium behavior; however, the theoretical modeling to predict their formation conditions is under development. Although a high degree of lattice distortion is expected in these gas hydrates due to highly polar and nonspherical molecules of refrigerants, this issue is not addressed in the van der Waals–Platteeuw theory. With this research gap, we formulate a lattice distortion theory for both pure and mixed refrigerant hydrates. For the first time, ab initio methodology comprising the spin-component scaled MP2 method with Dunning's basis set is implemented for estimating cavity potential of refrigerant hydrates. The extent of lattice distortion is documented in terms of reference chemical potential and enthalpy differences, which are obtained by regressing the Holder's equation with the experimental data of refrigerant hydrate formation. A critical observation is made that the reference properties linearly vary with the “Boltzmann weighted energy-well depth” of the guest. Analyzing the accuracy of the model using average absolute relative deviation between experimental and predicted pressure of hydrate formation, the proposed lattice distortion model outperforms the existing thermodynamic models for variety of pure and mixed refrigerant hydrates.     

Improvement of engineering properties of expansive soil using liming leather waste ash

Bulletin of Engineering Geology and the Environment - The expansive soils have always presented various challenges for geotechnical and civil engineers due to their low bearing capacity and high...     

Effect of Temper Condition on Stress Relaxation Behavior of an Aluminum Copper Lithium Alloy

Deformation behavior of an Al-Cu-Li alloy in different temper conditions (solutionized and T8) is investigated using stress relaxation tests. Fundamental parameters such as the apparent and physical activation volume, strain rate sensitivity, effective stress, and exhaustion rate of mobile dislocation density are determined from single and multiple relaxation tests. It was found that dislocation–dislocation interaction controls the kinetics of plastic deformation in the solutionized sample, whereas dislocation–precipitate interaction is the overriding factor in the presence of T₁ precipitates. The apparent activation volume was found to be significantly lower in the presence of T₁ precipitates compared with solutionized samples. Strain rate sensitivity and effective stress were found to be higher in the presence of T₁ precipitates. In addition, multiple relaxation tests showed that irrespective of microstructural features (solutes, semi-coherent precipitates), the mobile dislocation density reduces during the relaxation period. Further evidence regarding reduction in mobile dislocation density is obtained from uniaxial tensile tests carried out after stress relaxation tests, where both solutionized and T8 samples show an increase in strength. Additional discussion on relaxation strain is included to provide a complete overview regarding the time-dependent deformation behavior of the Al-Cu-Li alloy in different temper conditions.     

Coordination of dual setting overcurrent relays in microgrid with optimally determined relay characteristics for dual operating modes

Fault current magnitude in a microgrid depends upon its mode of operation, namely, grid-connected mode or islanded mode. Depending on the type of fault in a given mode, separate protection schemes are generally employed. With the change in microgrid operating mode, the protection scheme needs to be modified which is uneconomical and time inefficient. In this paper, a novel optimal protection coordination scheme is proposed, one which enables a common optimal relay setting which is valid in both operating modes of the microgrid. In this context, a common optimal protection scheme is introduced for dual setting directional overcurrent relays (DOCRs) using a combination of various standard relay characteristics. Along with the two variables, i.e., time multiplier setting (TMS) and plug setting (PS) for conventional directional overcurrent relay, dual setting DOCRs are augmented with a third variable of relay characteristics identifier (RCI), which is responsible for selecting optimal relay characteristics from the standard relay characteristics according to the IEC-60255 standard. The relay coordination problem is formulated as a mixed-integer nonlinear programming (MINLP) problem, and the settings of relays are optimally determined using the genetic algorithm (GA) and the grey wolf optimization (GWO) algorithm. To validate the superiority of the proposed protection scheme, the distribution parts of the IEEE-14 and IEEE-30 bus benchmark systems are considered.     

Outage probability and ergodic channel capacity of underlay device-to-device communications over $$kappa -mu$$κ-μ shadowed fading channels

Wireless Networks - Device-to-device (D2D) communication is observed as an emerging technique to offload the traffic from base station for improving the network performance. Outage probability (OP)...     

(S)-2-(Ethyl propionate)-(O-ethyl xanthate) and (S)-2-(Ethyl isobutyrate)-(O-ethyl xanthate)-mediated RAFT polymerization of N-vinylpyrrolidone

(S)-2-(Ethyl propionate)-(O-ethyl xanthate) (X1) and the newly synthesized (S)-2-(ethyl isobutyrate)-(O-ethyl xanthate) (X2) were used as the reversible addition-fragmentation chain transfer (RAFT) agents for the radical polymerization of N-vinylpyrrolidone (NVP). The former showed the better chain transfer ability in the polymerization at 60 °C. Kinetics study with X1 shows the psuedo-first order kinetics upto 45% monomer conversion. Molecular weight (M _n) of the resulted polymer increases linearly with increase in the monomer conversion upto around 45%. Polydispersity of the corresponding poly(NVP)s increase gradually from 1.2 to 1.9 with increase in the monomer conversion. Chain-end analysis of the resulted polymer by ¹H NMR shows clearly that polymerization started with radical forming out of xanthate mediator. Living nature of the polymerization was confirmed from the successful homo chain extension experiment and also the hetero-chain extension experiment involving synthesis of poly(NVP)-b-polystyrene amphiphilic diblock copolymer.