Measurement of enthalpies of vaporization of volatile heterocyclic compounds by DSC

An experimental procedure is proposed for direct measurement of the heat involved in the vaporization of volatile heterocyclic compounds. This technique consists on the vaporization of the liquid substance by a sudden decrease of the pressure then, the direct register of heat flow as function of time by differential scanning calorimetry. This procedure allows quantifying the enthalpy of vaporization of compounds such as tetrahydropyran, 2-methoxy-tetrahydropyran, N-morpholine and N-methyl-morpholine. Enthalpies of vaporization were measured in isothermal mode at T=298.15 K and then compared with results from the literature, which currently are obtained by vapour pressure measurements. © 2005 Akadémiai Kiadó, Budapest

Measurement of enthalpies of vaporization of volatile heterocyclic compounds by DSC

An experimental procedure is proposed for direct measurement of the heat involved in the vaporization of volatile heterocyclic compounds. This technique consists on the vaporization of the liquid substance by a sudden decrease of the pressure then, the direct register of heat flow as function of time by differential scanning calorimetry. This procedure allows quantifying the enthalpy of vaporization of compounds such as tetrahydropyran, 2-methoxy-tetrahydropyran, N-morpholine and N-methyl-morpholine. Enthalpies of vaporization were measured in isothermal mode at T=298.15 K and then compared with results from the literature, which currently are obtained by vapour pressure measurements. � 2005 Akad�miai Kiad�, Budapest

Characterization of Enterobacteriaceae Isolates Obtained from a Tertiary Care Hospital in Mexico, Which Produces Extended-Spectrum ?-Lactamase

The thermal behavior of hydrogels synthesized by solution polymerization between acrylamide, acrylic acid and diglycidyl acrylate (DGA) as a crosslinking agent was investigated. The structure of the hydrogel can be tightly controlled with the reaction temperature. This method produces a new type of hydrogels, which exhibit well defined structures at various scales of length simultaneously. These multi-structured hydrogels are hydrophilic, elastic, water insoluble, and soft polymers with an anisotropic optical response. The structure was observed by scanning electron microscopy (SEM), polarized light microscopy (PLM) and macroscopic visualization (CCD camera). In addition, structural transitions in the hydrogels were monitored by temperature modulated differential scanning calorimetry (TMDSC). Severe heating tests in an adiabatic oven were performed to analyze decomposition of the material. Fourier transform infrared (FTIR) spectroscopy was used to qualitatively analyze the hydrogels samples exposed to a sudden thermal treatment. " 2006 Springer-Verlag.",,,,,,"10.1007/s10973-005-7449-2",,,"http://hdl.handle.net/20.500.12104/40002","http://www.scopus.com/inward/record.url?eid=2-s2.0-33750033015&partnerID=40&md5=365b7afcc2cb2b00df95c29422d13675",,,,,,"2",,"Journal of Thermal Analysis and Calorimetry",,"51

Проблемы подготовки научных кадров высшей квалификации в условиях инновационных преобразований на военном факультете

Сложный и динамичный характер современной служебно-боевой деятельности, использование в ней новейших информационных технологий, образцов вооружения и военной техники; потребность общества в инициативных, грамотных специалистах

Разработка системы автоматического управления режимом работы тепловой сети

Доклад посвящен результатам разработки системы управления режимом подачи теплоносителя с целью снижения себестоимости доставки тепловой энергии потребителям

Polymeric hydrogels obtained using a redox initiator: Application in Cu(II) ions removal from aqueous solutions

Poly(acrylic acid-co-acrylamide) hydrogels were prepared via free-radical solution polymerization, crosslinked with ethylene-glycol-dimethacrylate, potassium persulfate/ammonium bisulfite as the initiator, and applied in the removal of Cu(II) ions from aqueous solutions. Molar ratios of acrylamide/acrylic acid moieties and the amount of crosslinking agent were varied to determine the swelling capacities of hydrogels and maximum metal uptake. Polymerization kinetics was investigated by 1H-NMR. Hydrogel physicochemical properties were characterized by nitrogen sorption measurements, elemental analysis, FTIR, and X-ray photoelectron spectroscopy (XPS). Swelling results indicated that hydrogels were swollen up to 27,500%. Hydrogels showed equilibrium Cu(II) adsorption capacities of 211.7 mg g-1 and fast kinetics (?20 min). Langmuir isotherm fitted adsorption equilibrium data. FTIR and XPS results helped in elucidating the presence of monodentate copper complex on the surface of hydrogels. A simple synthesis route of hydrogels using the redox initiator suggests the potential application in the removal of toxic metals from aqueous streams. � 2013 Wiley Periodicals, Inc

Removal of Cu(II) ions from aqueous streams using poly(acrylic acid-co-acrylamide) hydrogels

The adsorption of Cu(II) ions from aqueous solutions onto poly(acrylic acid-co-acrylamide) hydrogels was investigated. The hydrogels were prepared via free-radical solution polymerization using Irgacure 754 as a photoinitiator and ethylene glycol dimethacrylate as a cross-linking agent. Loading of acrylamide/acrylic acid moieties on the surfaces of hydrogels and the amount of cross-linking agent were varied to determine the maximum metal uptake. Polymerization kinetics was investigated by 1H NMR. The physicochemical properties of hydrogels were investigated by nitrogen sorption measurements, elemental analysis, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The 1H NMR results demonstrated that the polymerization reaction was carried out almost to completion and confirmed the absence of residual monomers. Swelling results indicated that, by appropriate selection of cross-linking agent amount and monomer ratio, hydrogels can be swollen up to 70,000%. Further characterization of the hydrogels showed rapid adsorption kinetics and equilibrium Cu(II) adsorption capacities of 121mgg-1. Cu(II) adsorption kinetic data followed pseudo-first-order kinetics. Adsorption equilibrium data were better fitted by a Langmuir isotherm. FTIR and XPS results indicated the presence of a tetradentate copper complex on the surfaces of hydrogels. The copper uptake achieved suggests the potential use of hydrogels to extract toxic metals from industrial aqueous streams. © 2010 Elsevier Inc

Influence of Chloride Salinity on Cadmium uptake by Nicotiana tabacum in a Rhizofiltration System

A hydroponic trial was conducted to study the effect of chloride salinity in simulated effluent on Cd accumulation by tobacco. Leaf surface area (LSA) and root surface area (RSA) measurements were incorporated as possible determinants of Cd uptake rate by plants. Results showed that individual plant differences in Cd content were normalized when including RSA to express Cd uptake rates by plants but not including LSA. A biotic ligand model (BLM) fitted to predict Cd uptake, estimated active and almost linear uptake of the free Cd2+ ion by tobacco plants, while virtually no changes in the chloride complex (CdCl+) uptake were predicted, presumably due to a rapid saturation of the hypothetical root sorption sites at the concentrations used in this trial. Nicotiana tabacum var. K326 is evidenced to be a species potentially suitable for biological wastewater treatment using rhizofiltration at concentrations commonly found in salt-affected wastewater, with high Cd accumulation (185 to 280 mg/kgdm) regardless of water salinity and tolerance up to 80 mmol/L NaCl