Structural and Initial Permeability Studies of Li-Zn-Co Ferrites

A series of cobalt substituted lithium zinc ferrites having the compositional formula Li_0.4–0.5xZn_0.2Co_xFe_2.4–0.5xO₄, where 0.00 ≤ x ≤ 0.1 in steps of 0.02, was prepared by the citrate precursor method. Structural studies on the prepared samples were carried out by using XRD and SEM measurements. Spinel phase structure of the samples was confirmed by XRD. From the XRD data the lattice parameter and the theoretical density were calculated. The experimental density was also determined using the Archimedes principle. Lattice parameter was observed to increase with increasing Co²⁺ ion concentration. The densification in both the cases, theoretical and experimental, shows an increase with composition. SEM studies carried out show that average grain diameter are in the range of 300 nm–650 nm and a fall is observed with increasing Co²⁺ ion content. The investigation on initial permeability as a function of composition and frequency were also undertaken. It is seen that there is decrease in the value of initial permeability with addition of Co content. The initial permeability and permeability loss show dispersion with frequency. Possible mechanisms contributing to the above processes are discussed.     

A new atom transfer radical polymerization initiator based on phenolphthalein for the synthesis of bis‐allyloxy functionalized polystyrene macromonomers

A new atom transfer radical polymerization (ATRP) initiator, namely 2‐(1,1‐bis(4‐(allyloxy)phenyl)‐3‐oxoisoindolin‐2‐yl)ethyl 2‐bromo‐2‐methylpropanoate, was synthesized starting from phenolphthalein, a commercially available and an inexpensive chemical. Well‐ defined bis‐allyloxy functionalized polystyrene macromonomers (M_n,GPC 4800–11 700 g mol^?1) with controlled molecular weight and narrow molecular weight distribution (1.05–1.09) were synthesized using ATRP by varying the monomer to initiator feed ratio. The presence of allyloxy functionality on polystyrene was confirmed by Fourier transform infrared and ¹H NMR spectroscopy. A kinetic study of polymerization revealed pseudo‐first‐order kinetics with respect to monomer consumption. Initiator efficiency was found to be in the range 0.80–0.95. Matrix‐assisted laser desorption ionization time of flight spectra showed a narrow molecular weight distribution with control over the molecular weight. The reactivity of the allyloxy groups on polystyrene was successfully demonstrated by quantitative photochemical thiol‐ene click reaction with benzyl mercaptan as the model thiol reagent. Furthermore, the thiol‐ene click reaction was exploited to introduce other reactive functional groups such as hydroxyl and carboxyl by reaction of α,α′‐bis‐allyloxy functionalized polystyrene with 2‐mercaptoethanol and 3‐mercaptopropionic acid, respectively. © 2014 Society of Chemical Industry     

Cold Simulation of momentum transfer of a metal droplet falling through slag systems possessing net-work structured fluids

Most of the high temperature smelting/refining processes involve falling of metal droplets through the slag systems. The slag systems comprising oxides viz., Al₂O₃, SiO₂, CaO, FeO, MgO, MnO etc., are essentially produced from the removal of ash and gangue from coke and/or ore during the metal extraction. At high temperatures these oxides form a network structured fluids. Momentum transfer phenomena of a falling sphere through these slag systems significantly influence the kinetics of the refining reactions occurring in the high temperature metallurgical reactors. It governs the metal quality including their productivity. The paper discusses cold simulation of the momentum transfer of a metal droplet falling through the slag systems possessing network structure.     

WEDM Parameter Optimization for Silicon@r-GO/Magneisum Composite Using Taguchi Based GRA Coupled PCA

Silicon - A combination of Taguchi methodology and Grey Relational Analysis (GRA) inturn coupled with principal component analysis (PCA) has been proposed through this paper. This methodology is...     

An all-graphene based transparent and flexible field emission device

All-graphene based cathode and anode structures were fabricated and their application as a flexible and transparent field emission device is presented. The graphene film was grown on a Cu foil by thermal chemical vapor deposition and later transferred to a polymer substrate through a hot press lamination technique. Multiwall carbon nanotubes (MWCNTs) were spin-coated onto a graphene film on a transparent, flexible substrate to form the cathode of the field emission device. A green-phosphor coated graphene-PET film was used as the anode. The device showed good transparency and flexibility as well as giving an appreciable emission current. The simple processing techniques used can easily be upgraded to a larger scale and be tailored for any transparent and flexible substrate. The device offers exciting applications of carbon nanostructures in foldable electronics.     

Survey of heat transfer mechanisms in a slurry bubble column

Heat transfer mechanisms in the bulk and distributor regions of a slurry bubble column are investigated based on the measurements of local heat transfer in a 0.28 m diameter Plexiglas column. The gas, liquid and solid phases used are oil‐free compressed air, tap water and 35 μm glass beads. The slurry concentration and superficial gas velocity are varied from 0 to 40 vol% and 0.05 to 0.30 m/s respectively. Measurements have been made with a fast response heat flux probe which provided local instantaneous heat transfer coefficients. The time‐averaged heat transfer coefficients in the bulk region were on average about 50% higher than the distributor region of the column. The wall region heat transfer coefficients are well predicted by the correlation of Deckwer et al. (1980). Heat transfer mechanism in column centre can be adequately described by the consecutive film and surface renewal model.     

Influence of calcium substitution on structural and electrical properties of substituted barium titanate

Ba_0.80−xCa_xPb_0.20Ti_0.90Zr_0.10O₃ ceramics (x = 0, 0.10 and 0.20) were synthesized by solid state reaction. Samples microstructure and dielectric, ferroelectric and piezoelectric properties were studied. Dielectric constant (?), coercive field (E_c), remanent polarization (P_r) and ratio of remanent to spontaneous polarization (P_r/P_s) were studied at different temperatures. Sample with x = 0.10 was found to have maximum and comparatively more stable P_r/P_s ratio over a wide temperature range. Dielectric loss was found to improve with increase in x whereas piezoelectric charge coefficient d₃₃ was found to decrease with increase in x.     

Fluidization and hydraulic behaviour of natural zeolite particles used for removal of contaminants from wastewater

Fluidization, bed expansion, pressure drop, and hydraulic characteristics of beds of natural zeolite particles have been studied for their potential application in the treatment of aqueous waste. The measurements in the bed of zeolite particles are compared with regular shaped glass beads. The bed of zeolite particles required to be fully fluidized before getting reproducible pressure measurements in the bed. This is attributed to their wider size distribution and resulting segregation. The mean size of the particles ranged from 550 to 900 µm. Minimum fluidization velocity was determined from pressure measurements below the distributor and compared with values from pressure measurements inside the bed. Experiments conducted with slurry out the bed showed that it could be easily drained in expanded mode from the column through a small diameter opening near the bottom.     

Hydrogenation of the Exocyclic Olefinic Bond at C-16/C-17 Position of ent-Kaurane Diterpene Glycosides of Stevia rebaudiana Using Various Catalysts

Catalytic hydrogenation of the exocyclic double bond present between C16 and C17 carbons of the four ent-kaurane diterpene glycosides namely rebaudioside A, rebaudioside B, rebaudioside C, and rebaudioside D isolated from Stevia rebaudiana has been carried out using Pt/C, Pd(OH)₂, Rh/C, Raney Ni, PtO₂, and 5% Pd/BaCO₃ to their corresponding dihydro derivatives with 17α and 17β methyl group isomers. Reactions were performed using the above-mentioned catalysts with the solvents methanol, water, and ethanol/water (8:2) under various conditions. Synthesis of reduced steviol glycosides was performed using straightforward chemistry and their structures were characterized on the basis of 1D and 2D NMR spectral data, including a comparison with reported spectral data.     

Controlled radical polymerization of n-hexadecyl methacrylate mediated by tris(2,2′-bipyridine)iron(III) complexes

Poly(n-hexadecyl methacrylate) (PHMA) with narrow molecular weight distribution has been synthesized by atom transfer radical polymerization (ATRP) and reverse ATRP of n-hexadecyl methacrylate (HMA) at 80 °C in N, N-dimethylformamide (DMF) using the CBr₄/tris(2,2′-bipyridine)iron(III) complex initiation system in the presence of 2,2′-azobisisobutyronitrile (AIBN). From the kinetic studies and molecular weight data, it reveals the controlled nature of polymerization. The effect of various reaction parameters on number-average molecular weight (M _n ) and molecular weight distribution (M _w /M _n ) have been investigated. For the reverse ATRP, the catalyst tris(2,2′-bipyridine)iron(III)complex, [Fe(bpy)₃]³⁺, played an important role in polymerization rate and M _w /M _n . The resulting PHMA that obtained by reverse ATRP shows the best control of molecular weights and its distribution as compared to normal ATRP system. PHMA has been characterized by different techniques such as GPC, XRD and NMR spectroscopy.