Effects of particle shapes to achieve angle of repose and force displacement behaviour on granular assembly

Circular or spherical particles in Discrete Element Method (DEM) possess limitations on achieving desired angle of repose for some granular assemblies. However, by using various shapes/clumps of particles, the limitation posed by the circular or spherical particles on achieving angle of repose can be minimized. In this paper, 2D DEM simulation has been used to investigate the effect of particle shapes on (a) angle of repose, where the aim is to achieve the angle of repose of 35° observed in a laboratory scale sand pile experiment, and (b) force displacement behaviour of granular assembly. The simulated results show that the particle shapes have strong influence on the angle of repose but have a less effect on force displacement behaviour on the granular assembly.     

Preparation of ultra‐high‐molecular‐weight polyacrylamide by vertical solution polymerization technique

A straightforward and novel methodology has been developed for the synthesis of ultra‐high‐molecular weight polyacrylamide (PAM) by vertical solution polymerization technique. By varying the concentrations of acrylamide monomer, three different grades of polymers (PAM‐V₁, PAM‐V₂, and PAM‐V₃) have been synthesized and compared with the series of different grades of PAM (PAM‐C₁, PAM‐C₂, and PAM‐C₃) synthesized through conventional solution polymerization technique. The synthesized grades PAM‐V₁, PAM‐V₂, PAM‐V₃, PAM‐C₁, PAM‐C₂, and PAM‐C₃ have been characterized by ¹H NMR, infrared spectroscopy, intrinsic viscosity measurement, molecular weight determination by gel permeation chromatography, and thermal analysis. Rheological analysis has been carried out on the aqueous solutions of various grades of PAMs. Swelling behavior of ultra‐high‐molecular weight PAMs has also been investigated. The flocculation performances of all grades have been investigated in kaolin suspension by settling and jar test methods. POLYM. ENG. SCI., 59:1175–1181 2019. © 2019 Society of Plastics Engineers     

Preparation and characterization of sol-gel derived yttria doped zirconia coatings on AISI 316L

A stable 4 mol% yttria-stabilized zirconia (YSZ) sol has been synthesized for coating stainless steel AISI 316L for biomedical applications. The sol was prepared by controlled hydrolysis of zirconium n-butoxide using acetylacetone and nitric acid as chelating agent and catalyst, respectively. X-ray diffractograms of calcined YSZ xerogel indicated a tetragonal structure at temperature as low as 400 °C. Stainless steel was dip-coated in transparent yellow YSZ sol followed by heat treatment between 400 and 600 °C for 2 h in air. A homogeneous and crack-free YSZ film was, thus, obtained on the stainless steel surface. Adhesion strength, measured by scratch test in progressive loading sequence on coated AISI 316L, showed 27 ± 3 N critical load. Corrosion performance of the surface coating was evaluated through open-circuit potential (OCP) measurement, impedance, polarization and chronoamperometry in Ringer's solution at 37 °C. The coating enhanced the pitting potential of the substrate. The metal ions released from AISI 316L was effectively controlled by the coating.     

An approach to suppress the blue-shift of photoluminescence peaks in coupled multilayer InAs/GaAs quantum dots by high temperature post-growth annealing

Effect of post-growth annealing on 10 layer stacked InAs/GaAs quantum dots (QDs) with InAlGaAs/GaAs combination capping layer grown by molecular beam epitaxy has been investigated. The QD heterostructure shows a low temperature (8 K) photoluminescence (PL) emission peak at 1267 nm. No frequency shift in the peak emission wavelength is seen even for annealing up to 700 °C which is desirable for laser devices requiring strict tolerances on operating wavelength. This is attributed to the simultaneous effect of the strain field, propagating from the seed layer to the active layer of the multilayer QD (MQD) and the indium atom gradient in the capping layer due to the presence of a quaternary InAlGaAs layer. Higher activation energy (of the order of ∼250 meV) even at 650 °C annealing temperature also signifies the stronger carrier confinement potential of the QDs. All these results demonstrate higher thermal stability of the emission peak of the devices using this QD structure.     

On the mechanism of material removal in electrochemical spark machining of quartz under different polarity conditions

Electrochemical spark machining (ECSM) process has been successfully applied for cutting of quartz using a controlled feed and a wedge edged tool. Contrary to the common belief that only cathode works as a tool, both cathode and anode have been used as a tool, i.e. ECSM with reverse polarity (ECSMWRP) as well as ECSM with direct polarity (ECSWDP) have been used to machine quartz plates. In ECSMWRP, deep crater on the anode (as a tool) and work-piece interface is formed because of chemical reaction. Chemical analysis of electrolyte solution after the ECSM experiments, also agrees with the feasibility of dissolution of quartz into solution due to chemical reaction. Reverse polarity cuts quartz plate at a faster rate as compared to the direct polarity. But in reverse polarity overcut, tool wear and surface roughness are higher as compared to the direct polarity machining. Magnified view of the machined surface also shows a difference in the mode of material removal in ECSMWDP and ECSMWRP. The cutting is possible even if we make auxiliary electrode of small size. In conclusion, experiments have revealed that cutting can be performed simultaneously at both the electrodes (anode and cathode) during ECSM.