Effect of hollow sphere size and size distribution on the quasi-static and high strain rate compressive properties of Al-A380–Al2O3 syntactic foams

Metal matrix syntactic foams are promising materials for energy absorption; however, few studies have examined the effects of hollow sphere dimensions and foam microstructure on the quasi-static and high strain rate properties of the resulting foam. Aluminum alloy A380 syntactic foams containing Al₂O₃ hollow spheres sorted by size and size range were synthesized by a sub-atmospheric pressure infiltration technique. The resulting samples were tested in compression at strain rates ranging from 10^?3 s^?1 using a conventional load frame to 1720 s^?1 using a Split Hopkinson Pressure-bar test apparatus. It is shown that the quasi-static compressive stress–strain curves exhibit distinct deformation events corresponding to initial failure of the foam at the critical resolved shear stress and subsequent failures and densification events until the foam is deformed to full density. The peak strength, plateau strength, and toughness of the foam increases with increasing hollow sphere wall thickness to diameter (t/D) ratio. Since t/D was found to increase with decreasing hollow sphere diameter, the foams produced with smaller spheres showed improved performance. The compressive properties did not show measurable strain rate dependence.     

Interplay Between Superconductivity and Antiferromagnetism in HoNi2B2C

A microscopic theory of interplay between superconductivity and antiferromagnetism in rare-earth nickel boride, HoNi₂B₂C is developed from first principles. Self-consistent equations for the superconducting order parameter Δ and magnetic order parameter Γ are derived using a Green’s function technique and an equation of motion method. The theory is applied to explain the experimental results in the antiferromagnetic superconductor HoNi₂B₂C. The present model explains the true coexistence of superconductivity and antiferromagnetism in this system. The behavior of the superconducting order parameter (Δ), the magnetic order parameter (Γ), the specific heat, the density of states, the free energy and critical field (H _c) is also studied for the system HoNi₂B₂C. Distinct features of the coexistence region are discussed. There is the convincing evidence that the theory is fully compatible with the key experiments.     

A practical silver nanoparticle-based adsorbent for the removal of Hg2+ from water

In this work, we describe the use of silver nanoparticles of 9 ± 2 and 20 ± 5 nm core diameter, protected by mercaptosuccinic acid (MSA) and supported on activated alumina for the removal of mercuric ions present in contaminated waters, at room temperature (28 ± 1 °C). These two nanoparticle samples were prepared by using two Ag:MSA ratios 1:6 and 1:3, respectively, during synthesis and were loaded on alumina at 0.5 and 0.3% by weight. The mechanism of interaction of silver nanoparticles with Hg(2+) ions was studied using various analytical techniques such as ultraviolet-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), dynamic light scattering (DLS), inductively coupled plasma-optical emission spectrometry (ICP-OES), energy dispersive analysis of X-rays (EDAX), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Interactions of the metal ion with the metal core, the surface head group and the monolayer functionality were investigated. A high removal ability of 0.8 g of mercury per gram of Ag@MSA was achieved in the case of 1:6 Ag@MSA. These two materials show better uptake capacity of Hg(2+) in the pH range of 5-6. The ease of synthesis of the nanomaterial by wet chemistry, capability to load on suitable substrates to create stable materials and affordable cost will make it possible to use this approach in field applications, especially for the treatment of Hg(2+) contaminated waters.     

Single- and few-layer graphene growth on stainless steel substrates by direct thermal chemical vapor deposition

Increasing interest in graphene research in basic sciences and applications emphasizes the need for an economical means of synthesizing it. We report a method for the synthesis of graphene on commercially available stainless steel foils using direct thermal chemical vapor deposition. Our method of synthesis and the use of relatively cheap precursors such as ethanol (CH(3)CH(2)OH) as a source of carbon and SS 304 as the substrate proved to be economically viable. The presence of single- and few-layer graphene was confirmed using confocal Raman microscopy/spectroscopy. X-ray photoelectron spectroscopic measurements were further used to establish the influence of various elemental species present in stainless steel on graphene growth. The role of cooling rate on surface migration of certain chemical species (oxides of Fe, Cr and Mn) that promote or hinder the growth of graphene is probed. Such analysis of the chemical species present on the surface can be promising for graphene based catalytic research.     

Impedance-spectroscopy analysis of oriented and mercerized bamboo fiber-reinforced epoxy composite

Bamboo fiber-reinforced epoxy composites were fabricated with untreated and alkali treated bamboo fibers. Dielectric, electric modulus, ac, and dc conductivity studies were carried out to rationalize the dielectric behavior of bamboo/epoxy composites. Composites of two fiber orientation parallel and perpendicular to the electric field were prepared. The dielectric behavior and electric modulus spectra of the composites were characterized using standard impedance analyzer. Dielectric properties were analyzed as a function of frequency (95 Hz–2 MHz) for temperatures in the range from 30 to 180 °C. Real part of dielectric constant (ε′), conductivity, and dielectric dissipation factor (tan δ) of 0° oriented bamboo/epoxy composites were higher than that of 90° oriented composites. Conductivity activation energy, tan δ, ε′, and volume resistivity decreased with increase in frequency at all the temperatures under study. Mercerization reduces the water absorption in bamboo fibers and thus improves corresponding dielectric properties of composites. Relaxation times 39.80 μs and 258.5 μs for 0° and 90° oriented bamboo/epoxy composites were calculated respectively from the relaxation peaks observed in electric modulus spectra at 180 °C.     

Optical and electrical properties and phonon drag effect in low temperature TEP measurements of AgSbSe2 thin films

Polycrystalline thin films of silver antimony selenide have been deposited using a reactive evaporation technique onto an ultrasonically cleaned glass substrate at a vacuum of 10-5 torr. The preparative parameters, like substrate temperature and incident fluxes, have been properly controlled in order to get stoichiometric, good quality and reproducible thin film samples. The samples are characterized by XRD, SEM, AFM and a UV-vis-NIR spectrophotometer. The prepared sample is found to be polycrystalline in nature. From the XRD pattern, the average particle size and lattice constant are calculated. The dislocation density, strain and number of crystallites per unit area are evaluated using the average particle size. The dependence of the electrical conductivity on the temperature has also been studied and the prepared AgSbSe2 samples are semiconducting in nature. The AgSbSe2 thin films exhibited an indirect allowed optical transition with a band gap of 0.64 eV. The compound exhibits promising thermoelectric properties, a large Seebeck coefficient of 30 mV/K at 48 K due to strong phonon electron interaction. It shows a strong temperature dependence on thermoelectric properties, including the inversion of a dominant carrier type from p to n over a low temperature range 9-300 K, which is explained on the basis of a phonon drag effect.     

Effect of partial dehydration on quality of canned potatoes

During commercial sterilization, mild to severe breakage of individual potatoes sometimes occurs and the outer layers of potatoes disintegrate into a floury texture referred to as sloughing. Four cultivars of potatoes namely Kufri Badshah, Kufri Bahar, Kufri Chandramukhi and HPS-1/13 were either treated with CaCl₂ or dehydrated before canning to reduce the sloughing. The extent of sloughing in terms of breakage observed visually depended on the cultivar of potatoes. Although CaCl₂ treatment reduces sloughing, it causes turbidity of the brine. Partial dehydration of potatoes before canning was helpful in reducing sloughing and it allowed a higher filling of potato solids in the can thereby increasing drained weight. HPS-1/13 cultivar was found most suitable for dehydrocanning.     

Anaerobic Degradability: Effect of Particulate COD

Batch bioassay tests were conducted to evaluate the effect of particulate chemical oxygen demand (COD) (CODP) on anaerobic digestion of wastewater at different ratio of food to microorganism (F/M). Synthetically prepared soluble and complex wastewaters were used. Experiments were conducted in seven sets of serum bottles maintained at F/M ranging from 0.18 to 2.0. Each set contained six bottles having a total COD (CODT) of 500 mg and CODP from 0 to 100%. Methane generation conforms to the first order rate kinetics. At all F/M, k?(day?1) decreased linearly with increase in fraction of CODP?(CODPF = CODP/CODT). Biomethane potential (BMP), and substrate and sludge activities also exhibited declining trend with increasing CODPF. The optimum value of F/M ranged from 0.57 to 0.68. The two variables, CODPF and F/M, were compounded to yield the ratio of CODP to microorganisms [M, measured as volatile suspended solids (VSS)]. On increasing the CODP/VSS from 0 to 0.9, the rate constant for methane generation is reduced by 81%. BMP30, percent sludge activity, and substrate utilization rate are lowered by 52–55%. These correlations could serve as useful guidelines to quantitatively assess the impact of particulate COD on biodegradability parameters.     

The solidification of metal-matrix particulate composites

The simplicity, economy and flexibility of solidification processes make them attractive methods for the production of particle-reinforced metal-matrix composites. At present, however, there is limited understanding of the phenomena occurring during solidification of these advanced materials. Nucleation and refinement of crystalline phases, physical and chemical interactions between dispersed particles and solidifying interfaces, and buoyancy-driven movement of the particles are areas where a knowledge base is beginning to be formed. Ultimately, the understanding of solidification processes in metal-matrix composites must become complete enough that microstructures can be tailored for specific applications.     

A model for primary and heterogeneous secondary reactions of wood pyrolysis

A chain growth model for heterogeneous secondary reactions is developed for the pyrolysis of large wood particles and the parameters determined by nonlinear optimization. The model takes both the volatile retention time and cracking and repolymerization reactions of the vapours with the decomposing solid as well as sutocatalysis into consideration. The extent of the secondary reactions is strongly influenced by the time and the ratio of the autocatalytic (propagation) reaction rate to noncatalytic (initiation) reaction rate. The wood which has a higher value of the autocatalytic/noncatalytic ratio also has a higher exothermic heat of reaction and yields a higher amount of final char residue. This fact confirms the heterogeneous secondary reactions lead to carbon enrichment of the final residue and are accompanied with an exothermic heat of reaction. The lower activation energies of the initiation and propagation reactions as compared to primary reactions (competitive reaction model consisting of weight loss and char forming reactions) confirm autocatalysis in large particles. The sealed reactor studies of small quantities of fine wood samples show that heterogeneous secondary reactions and not lower heating rates in large particles are the main source of char formed during the thermal decomposition of large wood particles. The model predictions are in agreement with the weight loss and temperature versus time curves over a wide range of particle size and furnace temperatures.