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Abstract  

The enthalpies of mixing of liquid binary Fe-Ge (17655 K) and Fe-Si (17505 K) alloys were determined using a high-temperature isoperibolic calorimeter. The thermodynamic properties of Fe-Ge melts were also studied by electromotive force method in the temperature range of 1250-1580 K. The comparison of our measurement results with literature data has been performed. The extreme negative values of integral enthalpy of mixing and alternating-sign deviations from Raoult's low for germanium can be explained by the influence of binary clusters formation.

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Abstract  

The amplitudes of the relaxation curves, as obtained by the Temperature-jump method have been used to measure simultaneously equilibrium constant and enthalpy for the reaction of complex formation of Ni2+ ion by 2,6-dihydroxobenzoic acid in the presence of a buffer. The experiments have been performed by changing the concentration of metal ion at constant ligand concentration andpH as in a complexometric titration. The points of such ‘dynamic titrations’ have been analysed by means of the concept of ‘normal reactions’ which enabled us to transform a set of coupled individual steps into a set of kinetically independent reactions. The potentialities of the dynamic titrations are discussed.

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Abstract  

The complexation of Np(V) with phosphate at elevated temperatures was studied by a synergistic extraction method. A mixed buffer solution of TRIS and MES was used to maintain an appropriate pH value during the distribution experiments. The distribution ratio of Np(V) between the organic and aqueous phases was found to decrease as the concentrations of phosphate were increased. Stability constants of the 1:1 and 1:2 Np(V)-HPO4 2− complexes, dominant in the aqueous phase under the experimental conditions, were calculated from the effect of [HPO4 2−] on the distribution ratio. The thermodynamic parameters including enthalpy and entropy of complexation between Np(V) and HPO4 2− at 25 °C–55 °C were calculated by the temperature coefficient method.

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Abstract  

The inclusion complex formation of riboflavin (RF) with hydroxypropyl-β-cyclodextrin (HP-β-CD) in water was investigated by 1H NMR, UV-vis spectroscopy, and solubility methods. A 1:1 stoichiometry and thermodynamic parameters of complex formation (K, Δc G 0, Δc H 0, and Δc S 0) were determined. Complexation was characterized by negative enthalpy and entropy changes due to prevalence of van der Waals interactions and hydrogen bonding between polar groups of the solutes. A partial insertion of RF into macrocyclic cavity was revealed on the basis of 1H NMR data and molecular mechanics calculation. Location of benzene ring of RF molecule inside the hydrophobic cavity of HP-β-CD results in an increase of aqueous solubility of the former.

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Abstract  

The ammonium manganese phosphate monohydrate (NH4MnPO4 · H2O) was found to decompose in three steps in the sequence of: deammination, dehydration and polycondensation. At the end of each step, the consecutive one started before the previous step was finished. The thermal final product was found to be Mn2P2O7 according to the characterization by X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy. Vibrational frequencies of breaking bonds in three stages were estimated from the isokinetic parameters and found to agree with the observed FTIR spectra. The kinetics of thermal decomposition of this compound under non-isothermal conditions was studied by Kissinger method. The calculated activation energies Ea are 110.77, 180.77 and 201.95 kJ mol−1 for the deammination, dehydration and polycondensation steps, respectively. Thermodynamic parameters for this compound were calculated through the kinetic parameters for the first time.

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Abstract

The DSC and TG data showed the dehydration process occurring over the range of 160–300 °C. The XRD patterns of the synthesized KNiPO4·H2O and the calcined product at 350 °C with exposing in the air over 8 h are indexed as the KNiPO4·H2O structure, whereas at 600 °C is indexed as KNiPO4 structure. Hence, these data confirmed that the water molecule was eliminated from the structure at 300 °C, after that the spontaneously reversible hydration–rehydration process was observed. The activation energy and pre-exponential factor were calculated by Kissinger, Ozawa, and KAS equations. According to the DSC curves, the enthalpy change (ΔH) of dehydration process can be calculated and was found to be 100.12 kJ mol−1. Besides, we suggested another new method to determine the isokinetic temperature value using spectroscopic data. The surface area of synthesized hydrate and its calcined product at 350 °C with exposing in the air at over 8 h were found to be 21.48 and 134.3 m2 g−1, respectively. The reversible hydration–rehydration process was observed, and the surface area of final product at 350 °C (aging time over 8 h) is higher than that of the synthesized compound. This behavior is important to develop alternative desiccant materials or other process based on the rehydration mechanism with increasing the surface area.

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From nanotechnology-based thermal insulation materials nano-ceramic thermal insulation coatings are generally considered to be the most critical because of contradictory technical data that could be founded in special literature. Complete agreement had not been already found about the mechanism how does their insulating effect take. In the Laboratory of Building Materials and Building Physics at Széchenyi István University (Győr, Hungary) several thermodynamic tests were made in order to find out thermodynamic process inside this material. Several building structures with different order of layers were tested with heat flow meter. Results showed that convective heat transfer coefficient cannot be taken account in usual way using this material as thermal insulation.

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