In Situ–Generated Zinc Bromide–Catalyzed α‐Bromination of Alkanones in Water

α‐Bromination of alkanones with bromine catalyzed by in situ–generated zinc bromide from zinc dust and bromine in water is investigated. Bromination with dioxane‐dibromide as a source of bromine does not require zinc dust and provides selectively α‐mono and α,α‐dibromo products in excellent yields when water is used as solvent.     

An efficient solvent-tuning approach for the rapid synthesis of thiazolidinone derivatives and the selective synthesis of 2-amino-4H-1,3-thiazin-4-one and dimethyl 3,3′-thiodiacrylates

Green synthetic approach has been developed for the rapid generation of thiazolidinone derivatives as crystallized products under catalyst-free conditions in water by polarity adjustment with ethyl lactate as a co-solvent in excellent yields. Additionally, interesting findings on the selective synthesis of 2-amino-4H-1,3-thiazin-4-one and dimethyl 3,3′-thiodiacrylates have been reported.     

Electrochemical deposition of uranium dioxide coatings on alloy 600: effect of annealing on Ni and Cu interlayer mixing

3.5–4.75 mg cm⁻² thick UO₂ coatings were electrodeposited using alkaline uranyl nitrate-ammonium oxalate bath on alloy 600 onto which nickel and copper interlayers were previously electrochemically formed. Micro laser Raman spectroscopy of annealed coating confirmed the formation of UO₂ by showing a peak at 447 cm⁻¹. Scanning electron microscopy showed uniform morphology with an average grain size of 1 µm. Glow discharge optical emission spectroscopy revealed no significant diffusion of nickel and copper into UO₂ due to annealing. Rutherford backscattering spectroscopy showed increased thickness of annealed coating. Scratch adhesion test indicated improved cohesive and adhesive strength of coating after annealing.

     

Hexaazatrinaphthylenes with Different Twists

A synthetic strategy that allows the induction of twist angles of different sizes in 5,6,11,12,17,18‐hexaazatrinaphthylene (HATNA) chromophores is reported. The different twist angles are accompanied by measurable changes in the emission and electrochemical characteristics of HATNA.     

High-speed imaging of n-heptane ignition in a high-pressure shock tube

Homogeneous and inhomogeneous ignition modes of n-heptane were studied using high-speed imaging in a high-pressure shock tube (HPST). n-Heptane, a fuel with strong negative temperature coefficient (NTC) behavior, was mixed with 4%-21% oxygen in argon or nitrogen and ignited over a wide temperature range (700–1250 K) and at elevated pressures (> 10 atm). Ultraviolet (UV) images of OH* emission were captured through a sapphire shock-tube end wall using a high-speed camera and a UV intensifier. The current study demonstrates the capability to study auto-ignition modes using high-speed imaging in a high-pressure shock tube. Both homogeneous and inhomogeneous auto-ignition events were observed with the latter generally confined to intermediate temperatures and reactive n-heptane mixtures. We also observed that conventional sidewall diagnostic signals are, in many cases, sufficient to identify inhomogeneous ignitions that are not accurately modeled under the assumption of spatially uniform chemistry.     

Dielectric Relaxations and Structures of Nanoclay in Solution Cast Poly(Ethylene Oxide)– Montmorillonite Clay Nanocomposites

The relative complex dielectric function, electric modulus and alternating current electrical conductivity spectra and complex impedance plane plots of aqueous solution cast poly(ethylene oxide)–montmorillonite clay (PEO–MMT) nanocomposite films were investigated over the frequency range 20 Hz to 1 MHz at ambient temperature. The intercalated and exfoliated structures of nanoclay dispersed in PEO matrix were recognized by the significant change in real part of dielectric function with clay concentration in the range 0%–20 wt%. The relaxation times corresponding to PEO chain segmental motion and ionic conduction relaxation processes were used to explore the interactions compatibility between PEO molecules and the dispersed MMT clay nanoplatelets and their effect on PEO chain dynamics. Real part of conductivity spectra of these nanocomposites over five decades of frequency has nonlinear behavior, which is influenced by the MMT clay concentration. The complex impedance plane plots confirm the bulk properties of these nanocomposites over the experimental frequency range.     

Mechanistic investigation of the sonochemical synthesis of zinc ferrite

In this investigation, an attempt has been made to establish the physical mechanism of sonochemical synthesis of zinc ferrite with concurrent analysis of experimental results and simulations of cavitation bubble dynamics. Experiments have been conducted with mechanical stirring as well as under ultrasound irradiation with variation of pH and the static pressure of the reaction medium. Results of this study reveal that physical effects produced by transient cavitation bubbles play a crucial role in the chemical synthesis. Generation of high amplitude shock waves by transient cavitation bubbles manifest their effect through in situ micro-calcination of metal oxide particles (which are generated through thermal hydrolysis of metal acetates) due to energetic collisions between them. Micro-calcination of oxide particles can also occur in the thin liquid shell surrounding bubble interface, which gets heated up during transient collapse of bubbles. The sonochemical effect of production of OH radicals and H₂O₂, in itself, is not able to yield ferrite. Moreover, as the in situ micro-calcination involves very small number of particles or even individual particles (as in intra-particle collisions), the agglomeration between resulting ferrite particles is negligible (as compared to external calcination in convention route), leading to ferrite particles of smaller size (6 nm).