Development and characterization of Al–Li alloys

Increased strength to weight ratio of aluminium–lithium alloys has attracted material scientists to develop these for aerospace applications. But commercial scale production of these alloys has always been slow in view of difficulties encountered during addition of lithium and in ensuring homogeneous billet composition. A new technique of Li addition has been adapted, which gives maximum recovery of Li in the billet. Using this technique, aluminium–lithium alloys of two different grades for aerospace application were cast. Billets were hot forged and rolled to the thickness range of 3–4 mm and heat-treated for different temper conditions. Mechanical properties were evaluated in T6 (solution treated and artificial aged), T8 (solution treated, cold worked and artificial aged) and T4 (solution treated and natural aged) temper conditions. Both alloys exhibit a strong natural aging response. Reversion for short periods at 180 °C results in decrease of strength. With artificial reaging strength reaches above the T4 temper condition level. Characterization was carried out using optical microscope (OM) and scanning electron microscope (SEM). Experimental investigation shows that addition of lithium at high melt temperature gives lower recovery of Li, and use of impure aluminium adversely affects the mechanical properties of the alloy in all temper conditions.     

Nanocrystalline diamond microspikes increase the efficiency of ultrasonic cell lysis in a microfluidic lab-on-a-chip

This research demonstrates that use of Nanocrystalline Diamond (NCD) microspikes in a microfluidic chamber increases the efficiency of mechanical cell lysis, as compared to a standard microfluidic surface such as glass. Microspikes made of nanocrystalline diamond were fabricated using standard MEMS techniques, and were incorporated in microfluidic chamber developed as part of a lab on a chip system. Mechanical cell lysis was performed on B16-F10 (ATCC CRL-6475) murine melanoma cells using ultrasonic vibration and the efficiency of cell lysis was determined. The microspikes puncture the cell membranes on collision greatly increasing the efficiency of cell lysis (about 400% as per fluorescence measurements) as compared to a non-textured glass surface. The effect of using cell disruption glass beads during ultrasonic lyses was also explored. This methodology of cell disruption could potentially make mechanical cell lysis a viable and preferred lysis option for lab-on-a-chip applications.     

Composition-independent Curie point (Tc) in ferroelectric (1 − x)PbTiO3–xBi(Li1/2Nb1/2)O3 solid solution

A new ferroelectric solid solution (1 − x)PbTiO₃–xBi(Li_1/2Nb_1/2)O₃ has been explored to develop high-temperature piezoelectric material. An interesting observation has been found regarding its Curie point (T_C) and tetragonal lattice strain (c/a − 1). With increasing composition (x), the Curie point (T_C) decreases up to x = 0.10 and thereafter remains constant. In concurrence with the T_C, the tetragonal lattice strain (c/a − 1) follows a similar trend. Neutron powder diffraction analysis suggests this anomalous behavior is due to the robust off-centering characteristic of the Bi⁺³ ion 6S² lone pair effect at the A-site compared to ions at B-site.     

Synthesis,characterization, and application of novel amphiphilic poly(D‐gluconamidoethyl methacrylate)‐b‐polyurethane‐b‐ poly(D‐gluconamidoethyl methacrylate) triblock copolymers

Novel amphiphilic ABA‐type poly(D ‐gluconamidoethyl methacrylate)‐b‐polyurethane‐b‐poly(D ‐gluconamidoethyl methacrylate) (PGAMA‐b‐PU‐b‐PGAMA) tri‐block copolymers were successfully synthesized via the combination of the step‐growth and copper‐catalyzed atom transfer radical polymerization (ATRP). Dihydroxy polyurethane (HO‐PU‐OH) was synthesized by the step‐growth polymerization of hexamethylene diisocyanate with poly(tetramethylene glycol). PGAMA‐b‐PU‐b‐PGAMA block copolymers were synthesized via copper‐catalyzed ATRP of GAMA in N, N‐dimethyl formamide at 20°C in the presence of 2, 2′‐bipyridyl using Br‐PU‐Br as macroinitiator and characterized by ¹H‐NMR spectroscopy and GPC. The resulting block copolymer forms spherical micelles in water as observed in TEM study, and also supported by ¹H NMR spectroscopy and light scattering. Miceller size increases with increase in hydrophilic PGAMA chain length as revealed by DLS study. The critical micellar concentration values of the resulting block copolymers increased with the increase of the chain length of the PGAMA block. Thermal properties of these block copolymers were studied by thermo‐gravimetric analysis, and differential scanning calorimetric study. Spherical Ag‐nanoparticles were successfully synthesized using these block copolymers as stabilizer. The dimension of Ag nanoparticle was tailored by altering the chain length of the hydrophilic block of the copolymer. A mechanism has been proposed for the formation of stable and regulated Ag nanoparticle using various chain length of hydrophilic PGAMA block of the tri‐block copolymer. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Increase of flow-through pores in rationally designed organosilica-PVDF nanocomposite membrane

Organosilica-polyvinylidenefluoride nanocomposite membrane has shown excellent performance in emerging technology of membrane distillation process for treatment of highly saline water stream. In present work, a systematic study using capillary flow porometry was carried out to evaluate the constricted part of the flow-through pores, which is active pores of the nanocomposite membranes. Mean flow pore size and distributions of the membrane pores were found to be influenced due to the phenomenon of micro-gelation by air exposure prior to the immersion in the coagulation bath of the preparation method, polymer concentration, polymer chain length and nature of the solvent in the casting dope solution. The best membrane in terms of the largest mean flow diameter of 0.12 μm with narrow distribution of flow-through pores were observed in the membrane with optimum organosilica content of 1.4 wt%.     

Accelerated hot corrosion studies of cold spray Ni–50Cr coating on boiler steels

In the current investigation Ni–50Cr powder was deposited on two boiler steels SA-213-T22 and SA 516 (Grade 70) by cold spray process. The hot corrosion performance of coated as well as bare boiler steels was evaluated in an aggressive environment of Na₂SO₄–60% V₂O₅ under cyclic conditions at an elevated temperature of 900 °C. The kinetics of the corrosion was approximated by the weight change measurements made after each cycle for a total period of 50 cycles. Each cycle consisted of 1 h heating in a tube furnace followed by 20 min cooling in ambient air. X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDAX) techniques were used to analyse the corrosion products. Both the uncoated boiler steels suffered intensive spallation in the form of removal of their oxide scales, which may be attributed to the formation of unprotective Fe₂O₃ dominated oxide scales. The Ni–50Cr coated steels showed lesser weight gains and the oxide scales remained intact till the end of the experiment. The phases revealed in the oxide scales of the coated specimens were mainly oxides of chromium and nickel and their spinels which are reported to be protective against the hot corrosion.