Modeling the coupling of reaction kinetics and hydrodynamics in a collapsing cavity

We introduce a model of cavitation based on the multiphase Lattice Boltzmann method (LBM) that allows for coupling between the hydrodynamics of a collapsing cavity and supported solute chemical species. We demonstrate that this model can also be coupled to deterministic or stochastic chemical reactions. In a two-species model of chemical reactions (with a major and a minor species), the major difference observed between the deterministic and stochastic reactions takes the form of random fluctuations in concentration of the minor species. We demonstrate that advection associated with the hydrodynamics of a collapsing cavity leads to highly inhomogeneous concentration of solutes. In turn these inhomogeneities in concentration may lead to significant increase in concentration-dependent reaction rates and can result in a local enhancement in the production of minor species.     

Effect of temperature of annealing on optical, structural and electrochromic properties of sol-gel dip coated molybdenum oxide films

The sol-gel dip-coating method is used for the preparation of MoO₃ thin films. The 6 layered MoO₃ films were prepared and annealed at various temperatures in the range of 200-350 °C. The band gap value for MoO₃ films were calculated from optical absorption measurements and it is in the range of 3.55-3.73 eV. XRD spectrum reveals (0 2 0) is the major diffraction plane for the films prepared above 250 °C, which reveals the formation of MoO₃ in α-orthorhombic phase. The films prepared at 200 °C and 250 °C exhibits amorphous nature. The FTIR spectrum confirms the presence of Mo-O-Mo and MoO bonds. Nanorods were observed in the SEM images in the case of MoO₃ films prepared above 250 °C. The films prepared at 250 °C exhibit maximum anodic diffusion coefficient of 9.61 × 10⁻¹¹ cm²/s. The same film exhibits the change in optical transmission of 58.4% at 630 nm with the optical density of 0.80.     

The crystal structure of bis-(L-threonine) copper(II).H2O

The crystal structure of bis-(L-threonine) copper (II).H₂O, Cu (C₄H₈NO₃)₂.H₂O has been determined by heavy atom and Fourier methods and refined by least-squares using visually estimated three-dimensional x-ray data of 893 reflections. The blue crystals are monoclinic, space groupP2₁ withα=11·02,b=4·90,c=11·16Å andβ=93·5°,Z=2. The finalR is 0·10. Coordination of copper is distorted square pyramidal with ligands intrans configuration. The conformation of one of the aminoacid ligand is identical with L_s-Threonine while the other has a conformation with torsional angleχ ^{1, 2}=?74(1)°.     

Electrophilic trifluoromethylation of simple inorganic salts: a one step route to trifluoromethylnitromethane, CF3NO2

Trifluoromethylnitromethane is readily synthesized in high yield from the electrophilic trifluoromethylation of NaNO₂.     

Syntheses of novel exo and endo isomers of ansa-substituted fluorophosphazenes and their facile transformations into spiro isomers in the presence of fluoride ions

Reactions of the dilithiated diols RCH2P(S)(CH2OLi)2 [R = Fc (1), Ph (2) (Fc = ferrocenyl)] with N3P3F6 in equimolar ratios at -80 degrees C result exclusively in the formation of two structural isomers of ansa-substituted compounds, endo-RCH2P(S)(CH2O)2[P(F)N]2(F2PN) [R = Fc (3a), Ph (4a)] and exo-RCH2P(S)(CH2O)2[P(F)N]2(F2PN) [R = Fc (3b), Ph (4b)], which are separated by column chromatography. Increasing the reaction temperature to -40 degrees C results in more of the exo isomers 3b and 4b at the expense of the endo isomers. The formation of the ansa-substituted compounds is found to depend on the dilithiation of the diols, as a reaction of the silylated phosphine sulfide FcCH2P(S)(CH2OSiMe3)2 (5) with N3P3F6 in the presence of CsF does not yield either 3a or 3b but instead gives the spiro isomer [FcCH2P(S)(CH2O)2 PN](F2PN)2 (6) as the disubstitution product of N3P3F6. The ansa isomers 3a and 3b are transformed into the spiro compound 6 in the presence of catalytic amounts of CsF at room temperature in THF, while 4a and 4b are transformed into the spiro compound [PhCH2P(S)(CH2O)2PN](F2PN)2 (7) under similar conditions. The novel conversions of ansa-substituted phosphazenes into spirocyclic phosphazenes were monitored by time-dependent 31P NMR spectroscopy. The effect of temperature on a transformation was studied by carrying out reactions at various temperatures in the range from -60 to +33 degrees C for 3b. In addition, compounds 3a, 3b, 4a, and 6 were structurally characterized. In the case of the ansa compounds, the nitrogen atom flanked by the bridging phosphorus sites was found to deviate significantly from the plane defined by the five remaining atoms of the phosphazene ring.     

Cobalt(II) complexes of creatinine

Summary Cobalt(II) complexes of creatinine [Co(creat)₂X₂] (X = Cl, Br, I or NCS) and [Co(creat)₂X₂(H₂O)₂] (X = HCO₂, HOCH₂CO₂ or CNCH₂CO₂) have been prepared. Their i.r. spectra show an increase in (NH) of the cyclic secondary amine group, compared to free ligand (3300 cm^–1), indicating that cyclic nitrogen is involved in coordination. The thiocyanate group coordinates through nitrogen and carboxylates coordinate as univalent unidentate ligands. The electronic spectra and magnetic moments suggest a d⁷ configuration for cobalt: a tetrahedral geometry (4.4 B.M.) for halide and thiocyanate complexes, and an octahedral geometry (5.0 B.M.) for the carboxylate complexes. On heating, the ligand moiety is lost and the respective cobalt halide or cobalt carboxylate is formed, which is converted finally into Co₃O₄. There is a correlation between the high intensity electronic transitions and the polarographic half-wave potentials.     

Where on Earth has our water come from?

The presence of water in the Earth has long been an enigma. However, computer modelling techniques have shown that the adsorption of water onto the fractal surfaces of interplanetary dust particles, which are present in the planetary accretion disk, is sufficiently strong to provide a viable origin of terrestrial water.     

Developing empirical relationships to predict grain size and hardness of the weld nugget of friction stir welded AA7075-T6 aluminium alloy joints

Experimental Techniques - High-strength, precipitation-hardening AA7075-T6 alloy is used extensively in aircraft primary structures. Friction stir welding process is an emerging solid state joining...