Authors:M. D. Baró, N. Clavaguera, S. Bordas, M. T. Clavaguera-Mora, and J. Casas-Vázquez
The kinetics of bulk crystallization of Se61.5Ge15 4Sb23.1 glasses was investigated from their thermal behaviour. In the thermal characterization of a glass the recrystallization temperature is highly dependent on both the rate of heating and the thermal history of the glass. Vitreous samples were prepared by quenching. From ratedependent curves it was found that the recrystallization process obeys first-order kinetics with an apparent activation enthalpy of 48±5 kcal/mole. Further analysis allows determination of both the activation enthalpy,H=90±4 kcal/mole, and the kinetic exponent of the Avrami equation,n=1.9±0.3.
The heterogeneous isotopic exchange reactions in strontium polymolybdates of Sr2+ and MoO42- ions in the strontium nitrate and sodium molybdate solutions have been studied using 90Sr and 99Mo as tracers. Electrometric methods have been used to study the compositions of strontium molybdates obtained by adding strontium chloride to a progressively acidified solution of sodium molybdate. It has been found that the exchange fraction increases with increasing chain length of strontium polymolybdate. The exchange equilibrium constant (Kex) has been calculated between 298 and 348 K as well as DG°, DH° and DS°. The results indicate that Sr2+ cations have a much higher affinity for exchangers than MoO42- anions. By fitting the data to the Dubinin-Radushkevich (D-R) isotherm it has been shown that the exchange capacity (Xm) for both ions is affected by the ion adsorption process at low temperatures and by the ion exchange process at high temperatures. At high concentrations, the recrystallization process contributes to on the cation exchange but is ineffective on the anion exchange mechanism.
Authors:R. Brodzinski, H. Miley, J. Reeves, and F. Avignone
Three years ago, state-of-the-art low-background germanium spectrometry was discussed, and speculations were advanced as to the origin of the remaining background. Some of those speculations have been shown to the incorrect. Contemporary lead shielding contains 100 Bq/kg of210Pb. Our 450-year-old lead was shown to contain <100 mBq/kg A high purity electroformed copper Marinelli shield was placed around the detector with no efffect on the background, which implied that the source is other than the 450-year-old shield. A new limit on the210Pb in this old lead shield is <9 mBq/kg. Electroformed copper components were found to contain226Ra and228Th contaminations at levels of 3500 and 110 Bq/kg, respectively. High purity H2SO4, recrystallized CuSO4, and a BaSO4 scavenge in the electroforming bath have reduced these contaminations to <25 and 9 Bq/kg, respectively. In copper, cosmic ray induced nuclear reactions are now the dominant source of raioactivity. For example,58Co can be readily measured after only a 24-hour exposure at sea level. A new germanium spectrometer containing 2150 grams of 87.44% enriched76Ge has been fabricated to mitigate the effect of cosmogenic68Ge in the background. Current background spectra are presented, and potential sources identified.
Authors:L. C. Morais, J. Dweck, F. R. Valenzuela-Diaz, and P. M. Büchler
The treatment of the effluents of dairy product industries containing lactose is done by a biological process, which reduces considerably the original amount of that sugar. Although the final residual content of lactose is small after treatment, it may cause the eutrophication and/or the superfertilization of the water, which provokes vegetation growth on the water surface, hindering the navigability and increasing the consumption of the dissolved oxygen necessary to the life of the fishes of the river or sea where the treated effluent is poured. In dairy industry, after proper initial processing steps of waste treatment, lactose, as it is water soluble, may still be present in the outgoing effluents. A complementary step by using organophilic clay adsorption, as a further treatment of these effluents, may enhance antipollution procedures, decreasing its final content in the effluents. The present paper deals with the characterization, by thermal analysis of different lactose products, which may be present in the different processing steps as it dissolves in water and then it is recrystallized from it, as well as after being adsorbed by organophilic clay from those effluents, which are very diluted lactose aqueous solutions.
Authors:R. Ceolin, V. Agafonov, A. Gonthier-Vassal, H. Szwarc, J. Cense, and Ph. Ladure
Flutamide usually crystallizes in the orthorhombic non-centrosymmetric space group Pna21 (from I) and melts atTfus=384 K with ΔfusH=30 kJ·mol−1. It may be obtained in the glassy state (Tg=272 K) by quenching the melt. Although evidence of polymorphism could not be obtained by means of crystallography, DSC studies
of the recrystallization process indicate that a metastable form (form II) occurs first and is transformed into the stable
form at room temperature. ΔH for the transition I→II (2.52 kJ·mol−1) is close to the difference in energy (about 2 kJ·mol−1) calculated for the two possible conformers of flutamide.
Authors:A. Yaghmur, A. Aserin, I. Tiunova, and N. Garti
The five-component system is quite unique since it allows formation of reverse micelles with hydrophilic ethoxylated alcohol in the presence of ethanol and it facilitates dilution by water/propylene glycol (1,2-propanediol, PG) aqueous phase, all the way from a water-in-oil (W/O) microemulsion via a bicontinuous phase to an oil-in-water (O/W) microemulsion.The surfactant/alcohol/PG can strongly bound water in the inner phase so that it freezes below –10°C and acts in part as bound water and in part as non-freezable water. Upon dilution to >30 mass% aqueous phase (water/PG at constant mass ratio of 1/1) the system becomes bicontinuous and the aqueous layers are composed again from bound water. Even after complete inversion to O/W microemulsions the water in the continuous phase is strongly interacting with the PG/surfactant and remains bound or non-freezable. Water/PG/ethanol have a strong effect on the head groups (freezing below -10°C) and also on the hydrophobic tails (recrystallizing and melting) at lower temperature when dilution exceeds 45 mass% water/PG (1/1).No free water was detected neither in the W/O microemulsion's inner droplet domains nor when the microemulsion was either bicontinuous or when it was inversed to O/W. Continuous phase of resulting O/W microemulsion apparently is based on water/PG at a mass ratio of 1/1.
Authors:P. Claudy, J. M. Letoffe, J. J. Counioux, and R. Cohen-Adad
The non-equilibrium region of the phase diagramxLiCl-(1−x)H2O (0<x< 0.18) has been studied by means of a Mettler TA 2000 B heat flow differential scanning calorimeter. The metastable lines of the diagram have been established and the different phases obtained explained. A region has been found where the glass formed cannot recrystallize, the eutectic line being below the temperature of the transition glass.
Authors:J. Giusti, G. G. T. Guarini, L. Menabue, and G. C. Pellacani
The thermal behaviour of single-crystals of the title compound has been investigated by means of thermal methods supported by optical microscopy. A complex change takes place on heating. After the loss of the two water molecules, leading to an amorphous phase, recrystallization takes place. This results in a solid (probably an anhydrous form) which reacts further, through partial liquefaction, to yield a red crystalline product whose structure has been characterized via X-ray powder spectra and electronic and IR spectroscopy.
Inorganíc polymers such as silicates, borates and phosphates can be transformed into amorphous solids by heating to an appropriate
temperature. Thermal amorphization can be obtained by: 1. thermal dissociation of a crystalline compound, 2. distortion of
the crystal structure of a solid during prolonged heat treatment, without change of its chemical composition. The specificity
of the materials received, the crystallochemical conditions necessary for the amorphization which takes place, and the high-temperature
processes of internal structure reconstitution and recrystallization in the amorphous products are considered.
Authors:Noufissa Zanati, Michael Mathews, Indika Perera, John Moran, Jean Boutros, Alan Riga, and Mekki Bayachou
The long-term goal of this investigation is to study the effects of increased cholesterol levels on the molecular activity
of membrane-bound enzymes such as nitric oxide synthase, that are critical in the functioning of the cardiovascular system.
In this particular investigation, we used differential scanning calorimetry (DSC) and dielectric thermal analysis (DETA) to
study the effect of added cholesterol on melting/recrystallization and dielectric behavior, respectively, of phosphatidylcholine
(PC) bilayered thin films. We also used electrochemical methods to investigate the effect of added cholesterol on the redox
behavior of the oxygenase domain of nitric oxide synthase as a probe embedded in the PC films. The results show that added
cholesterol in the PC films seems to depress the molecular dynamics as indicated by lowered current responses in the presence
of cholesterol as well as a slight increase of the transition temperature in the overall two-phase regime behavior observed
in PC–cholesterol films. These results are rationalized in the context of the general DSC and DETA behaviors of the PC–chol