Short fiber-reinforced thermoplastic elastomers from blends of natural rubber and polyethylene

Thermoplastic elastomer blends of natural rubber (NR) with high density polyethylene (HDPE) and with low density polyethylene (LDPE) were reinforced with short silk fiber. Processing characteristics such as torque and temperature developed during mixing and the effect of processing parameters such as nip gap and number of passes in the mill necessary to secure maximum orientation of the fibers in the blends were studied. A small nip gap and a single pass in the mill were found to give best results. Of the different mixing sequences studied, the sequence where short fibers followed by rubber were added to the molten thermoplastic was found to give a uniform dispersion of fibers. Fiber breakage and the change in aspect ratio of the fibers after mixing were also examined. It was observed that, as a direct consequence of the mixing sequence, each fiber was coated with a layer of thermoplastic. Although the properties improved on the addition of the dry bonding system of silica–resorcinol–hexamethylenetetramine, the comparatively long curing time required for full development of adhesion between the fibers and the matrix proved to be a major disadvantage associated with the incorporation of the bonding system. The tensile and tear properties were substantially enhanced, but the ultimate elongation decreased sharply with increasing loading of short fibers in the blends. The effect of fiber orientation and the development of anisotropy in the properties was also noted. Scanning electron microscopy (SEM) studies of the benzene-extracted surfaces of the NR/HDPE (high density polyethylene) blends substantiated the theory of fibers behaving like “mechanical anchors” between the rubber and thermoplastic phase. The effect of fiber loading on the tear and tensile properties of the blends of NR/LDPE with varying blend ratios was studied. Most pronounced improvement in the properties on the addition of short fibers was observed in the high rubber blends. As the plastic content in the blends increased, the short fibers were found to have a lesser influence on the properties. SEM photomicrographs of the tensile and tear fracture surfaces indicated the fiber orientations and the effect of orientation, fiber loading, and blend ratios on the nature of fracture.     

Simulations of Bubble Column Reactors Using a Volume of Fluid Approach: Effect of Air Distributor

Two‐ and three‐dimensional numerical simulations have been performed on a laboratory scale bubble column reactor using a volume‐of‐fluid approach. The effect of hole‐size and superficial gas velocity on the bubble size distribution and their trajectories has been investigated on a 20 cm diameter and 1 m high cylindrical reactor. All simulations were performed in a transient manner using a FLUENT solver. Surface tension between two phases has been modelled as a body force with a constant value. Turbulence was modelled using the k‐? turbulence approach. A comparison between simulation predictions and the reported experimental studies has shown a good agreement.     

Splat-quenching of lead in vacuum

A gun assembly for splat-quenching of materials in vacuum or controlled ambients has been set up. A metastable h c p structure (a=3.48 Å, c=5.59 Å, c/a=1.60) has been observed in splat quenched pure lead. The h c p phase is stable up to 270° C and transforms to the equilibrium f c c structure on heating in the electron microscope. The transformation has also been confirmed by DTA. The observed h c p structure appears to be stabilized by traces of oxygen as well as a high rate ( 10⁸ K sec^–1) of cooling. No such structure has been observed in vapour-quenched films under similar conditions.     

A waveguide-based two-step approach for measuring complex permittivity tensor of uniaxial composite materials

A rectangular waveguide-based two-step approach for measuring the complex permittivity tensor of uniaxial highly lossy nonmagnetic composite materials in the S-band is presented. In the proposed scheme, two independent sets of reflection and transmission coefficient data for each material-under-test (MUT) are measured by aligning the electric field vector of the dominant TE/sub 10/ mode in the rectangular waveguide parallel and perpendicular to the fiber orientation of the uniaxial sample, respectively. The complex permittivity tensor of the MUT is determined from these measured scattering data in two successive steps. The first step uses the newly proposed analytical approach, which can resolve the ambiguity problem, commonly encountered with samples of electrical length larger than a wavelength. In the second step, nonlinear least square optimization algorithms are employed, where the material parameters using the first step are now used as the initial guess. The proposed two-step approach is valid for multilayered structures, and the local minima problem commonly encountered with optimization routines are also avoided. A number of carbon-fiber composite materials along and, transverse to the fiber orientation are measured using the proposed method. Finally, a brief uncertainty analysis, to study the effect of air-gaps on waveguide measurements, is carried out.     

Sintering behavior, microstructure and properties of TiC-FeCr hard alloy

TiC based cermets were produced with FeCr, as a binder, by conventional P/M （powder metallurgy） to near 〉97% of the theoretical density. Sintering temperature significantly affects the mechanical properties of the composite. The sintering temperature of 〉1360℃ caused severe chemical reaction between TiC particles and the binder phase. In the TiC-FeCr cermets, the mechanical properties did not vary linearly with the carbide content. Optimum mechanical properties were found in the composite containing 57wt% TiC reinforcement, when sintered at 1360℃ for 1 h. Use of carbon as an additive enhanced the mechanical properties of the composites. Cermets containing carbon as an additive with 49wt% TiC exhibited attractive mechanical properties. The microstructure of the developed composite contained less or no debonding, representing good wettabifity of the binder with TiC particles. Homogeneous distribution of the TiC particles ensured the presence of isotropic mechanical properties and homogeneous distribution of stresses in the composite. Preliminary experiments for evaluation of the oxidation resistance of FeCr bonded TiC cermets indicate that they are more resistant than WC-Co hardmetals.     

Complex Electric Modulus Spectroscopy of (MnFe<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/CuTl-1223 Nanoparticles-Superconductor Composites

Manganese ferrite (MnFe₂O₄) nanoparticles and Cu_0.5Tl₀.₅Ba₂Ca₂Cu₃O_10?δ(CuTl-1223) superconducting phase were synthesized by sol-gel and solid-state reaction methods, respectively. Different contents of MnFe₂O₄ nanoparticles were added in CuTl-1223 superconducting matrix to get (MnFe₂O₄)_x/CuTl-1223; x =? 0～2.0 wt% nanoparticles-superconductor composites. Complex electric modulus spectroscopy measurements of (MnFe₂O₄)_x/CuTl-1223 composites were carried out at different test frequencies from 20 Hz to 10 MHz and at different operating temperatures from 78 to 253 K to analyze and interpret the dynamical aspects of electrical transport phenomena (i.e., such as carrier hopping rate, conductivity, and blocking factor). The complex electric modulus spectra showed the effects of both grains and grain-boundaries on electrical properties. The capacitance of grain-boundaries was found higher than that of grains. The capacitive behavior of grains was increased and that of grain-boundaries was decreased with increasing operating temperature for all these samples. Blocking factor of these composites was increased with increasing contents of MnFe₂O₄ nanoparticles. Shifting of peaks in imaginary part of modulus spectra towards lower frequency with increasing contents of these nanoparticles showed non-Debye type relaxation phenomenon in the material.     

Synthesis and characterization of ZnO nanostructures with varying morphology

Uniform fine particles of zinc oxide were prepared in three different morphologies and sizes by the controlled precipitation process from aqueous solutions of zinc nitrate in the presence of ethylene glycol. Ammonium hydroxide solution was used as the precipitant. Composition of the reactant solution, pH and temperature significantly affected the particle uniformity with respect to shape and size. Uniformity in the particles morphological feature was achieved under a narrow set of experimental conditions. pH of the reactant solutions and isoelectric point of zinc oxide were considered the master variables, controlling the particle size. One of the batch of the as-prepared zinc oxide particles was calcined at \(750{^{\circ }}\hbox {C}\), which increased its crystallinity, changed its various lattice parameters, Zn–O bond length and preferred orientation of the crystal hkl planes. Calcination had little effect on the original morphology of the zinc oxide particles.     

Effect of Charge Reservoir Layer on the Structural and Transport Properties of CuTlBa<Subscript>2−Y</Subscript>Sr<Subscript><Emphasis Type="Italic">Y</Emphasis></Subscript>-1223 (<Emphasis Type="Italic">Y</Emphasis> = 0 − 0.25) Superconductor

The bulk superconducting composites Cu_0.5Tl_0.5 Ba_2?YSr _Y Ca₂Cu₃O₁0?δ (Y = 0, 0.15, and 0.25) have been synthesized at an ambient pressure. The techniques used to characterize the samples were X-ray scans, Fourier transform infrared spectroscopy (FTIR), and dc resistivity (ρ) measurements. In CuTl-1223 system, we replaced Sr atom at Ba site and studied the superconducting properties of squeezed charge reservoir layer (CRL). From the XRD analysis, it is confirmed that the samples have orthorhombic structure and the dimensional parameters of the unit cell suppressed with the dopant atom which is most probably due to small in size of Sr atom as compared with Ba. The normal-state resistivity and critical temperatures, i.e., T _c (R = 0) and \(T_{\mathrm {c}}^{\text {onset}}\) are observed to be suppressed. The lower values of critical temperature T _c (R = 0) and activation energy U _o (eV) might be possible due to a weak flux pinning. Accordingly, a reduction of weak links and enhanced insulating nature of inter-grain coupling were observed with the doping of Sr atom in CRL. Moreover, the doping in CRL of Sr atom is also confirmed with the FTIR technique. The intrinsic parameters, i.e., coherence length ξ _c(0), crossover temperatures (T _3D?2D), inter-layer coupling (J), etc. were calculated by fluctuation-induced conductivity (FIC) analysis.     

Macromechanics study of stable fatigue crack growth in Al–Cu–Li–Mg–Ag alloy

This study was made on a fresh variety of Al–Li base alloy to investigate the role of ageing precipitates and microstructure dimensions in the fatigue crack growth resistance. The fatigue crack growth rate was measured in three different states of the material (i.e. base metal in T8 condition, friction stir weld and laser beam weld in full‐aged condition). Metallurgical analysis showed that the base metal in T8 temper is precipitation hardened by an equivalent amount of δ′ (AL₃Li), T₁ (AI₂CuLi) and θ′ (AI₂Cu) precipitates. The friction stir weld retained the morphology of strengthening precipitate; however, coarsening of Cu containing precipitates has occurred. On the other hand, laser beam weld showed a different type of CuAl phase morphology, which is characteristic of cast metal. The results of fatigue tests confirmed that fatigue crack growth resistance largely depends on microstructural features, specifically the strengthening phases. The fatigue crack resistance was in the order of base metal > laser beam weldment > friction stir weldment. The CuAl phase played a vital role in the crack closure of the laser beam weldment, thus enhancing the fatigue life as compared with the friction stir weldment, which was evident from the plot between log of da/dN (crack growth in each cycle) and log of ΔK (stress intensity range).