Kinetic Analysis of Calorimetric Measurements of Niobium–Aluminum Nb/Al Multifilament Strands

The formation of different phases for the reaction of Nb and Al in M/s Hitachi Ltd made wires using differential scanning calorimetry (DSC) has been investigated. The interfacial diffusion reaction has been studied in the temperature range 100–990 °C. Niobium (Nb) and aluminum (Al) react to form the phase NbAl₃, subsequently NbAl₃ reacts with the remaining Nb to form the A15 phase. The interfacial reactions play an important role. At higher heating rates, NbAl₃ and bcc‐structured NbAl are formed prior to the formation of Nb₃Al, but at lower heating rates the phase observed indicates σ phase Nb₂Al. DSC has been performed at different heating rates under nonisothermal conditions aimed to measure activation energy of crystallization for different phases: employing Kissinger's equation, Matusita–Sakka theory, and the Augis‐Bennett method. Activation values calculated from these three different methods are found to be in good agreement with each other. The activation energy for the first phase (NbAl₃) is lower than the other two phases (Nb₃Al) A15 phase and Nb₂Al, suggesting that NbAl₃ formation occurs easily. The value of n relating to the nucleation and growth mechanisms has also been calculated using the modified Kissinger method at different temperatures.     

Enthalpies of hydrogen-bonded butylamine-chloroform complexes

Enthalpies of mixing of isomeric butylamine with chloroform were determined at 30°C by a Calvet-type microcalorimeter. The system showed highly exothermic behaviour due to hydrogen-bonded complex formation on mixing. The enthalpies of complex formation were calculated by means of a thermo-chemical cycle and the values vary from 1-aminobutane to 2-amino-2-propane complexes. NCL Communication No. 4255     

Excited state intramolecular charge transfer reaction in binary mixtures of water and tertiary butanol (TBA): alcohol mole fraction dependence

The excited state intramolecular charge transfer reaction of 4-(1-azetidinyl)benzonitrile (P4C) has been studied in water-tertiary butanol (TBA) mixtures at different alcohol mole fractions by using steady state and time-resolved fluorescence spectroscopy. The ratio between the areas under the locally excited (LE) and charge transferred (CT) emission bands is found to exhibit a sharp rise at alcohol mole fraction approximately 0.04, a value at which several thermodynamic properties of this mixture is known to show anomalous change due to the enhancement of H-bonding network. The radiative rate associated with the LE emission also shows a maximum at this TBA mole fraction. Although the structural transition from the water-like tetrahedral network to the alcohol-like chain is reflected in the red shift of the absorption spectrum up to TBA mole fraction approximately 0.10, the emission bands (both LE and CT) show the typical nonideal alcohol mole fraction dependence at all TBA mole fractions. Quantum yield, CT radiative rate as well as transition moments also exhibit a nonideal alcohol mole fraction dependence. The time-resolved emission decay of P4C has been found to be biexponential at all TBA mole fractions, regardless of emission collection around either the LE or the CT bands. The time constant associated with the slow component (tau(slow)) shows a minimum at TBA mole fraction approximately 0.04, whereas such a minimum for the fast time constant, tau(fast) (representing the rate of LE --> CT conversion reaction) is not observed. The nonobservation of the minimum in tau(fast) might be due to the limited time resolution employed in our experiments.     

Interaction between the conjugated polyelectrolyte poly{1,4-phenylene[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} copolymer and the lecithin mimic 1-O-(l-Arginyl)-2,3-O-dilauroyl-sn-glycerol in aqueous solution

In this paper, the interaction between the water-soluble conjugated polyelectrolyte poly{1,4-phenylene[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} copolymer and the amino acid glyceride conjugate 1-O-(L-arginyl)-2,3-O-dilauroyl-sn-glycerol dichlorohydrate (a mimic for the phospholipid lecithin) has been studied in aqueous solution by electronic spectroscopy (absorption and fluorescence) and small-angle neutron scattering (SANS). A significant increase in the polymer fluorescence and blue shift in its emission are observed on association with the surfactant. This is suggested to be due to breakup of polymer aggregates. In addition, the spectroscopic and photophysical data suggest this is followed by the vesicle to ribbon transition characteristic of this surfactant, leading to incorporation of single chains of the polymer within mixed polymer-surfactant aggregates. Support for this comes from preliminary SANS measurements, from which evidence for polymer dissolution and formation of two-dimensional structures has been obtained.     

Preparation, characterization, and photocatalytic activity of sulfate-modified titania for degradation of methyl orange under visible light

Hydrated titania was prepared by a sol-gel method, taking tetraisopropyl orthotitanate as starting material, and then promoted with different weight percentages of sulfate by an incipient wetness impregnation method. The materials were characterized by various advanced techniques such as PXRD, BET surface area, N(2) adsorption-desorption measurements, FTIR, and SEM. Analytical results demonstrated that TiO(2) is mesoporous in nature, and sulfate modification could inhibit the phase transformation and enhance the thermal stability of TiO(2). It was also found that sulfate modification could reduce the crystallite size and increase the specific surface area of the catalysts. The degradation of methyl orange under solar radiation was investigated to evaluate the photocatalytic activity of these materials. Effects of different parameters such as pH of the solution, amount of catalyst, additives, and kinetics were investigated. At 2.5 wt% sulfate loading, the average percentage of degradation of methyl orange was nearly two times than that of neat TiO(2). The photocatalytic degradation followed first-order kinetics.