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Abstract  

Starting from tabulated thermodynamic data of stable compounds in the Mo−O−Cl system, phase diagrams for the Mo−O−Cl system were developed on the basis of GIBBS' phase law by means of thermodynamic calculations. The behaviour of molybdenum trioxide in a temperature gradient tube was investigated experimentally under chlorinating conditions, using99Mo as indicator. The thermochromatografically separated compounds were characterized by their deposition temperature in the temperature gradient tube and by an activation analytical determination of their Mo/Cl ratio. The experimental results were compared with the calculated phase diagram.

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The important role of thermoanalytical methods in the field of pharmaceutical and galenic research is outlined. The thermodynamic stability of polymorphic forms of a substance is discussed.

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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  

Adsorption of cerium on lead dioxide from aqueous solutions has been studied as a function of shaking time, amount of adsorbent, pH, concentration of the adsorbate and temperature. The adsorption process is endothermic and the distribution coefficient (KD) increases with increasing temperature. The data fit very well the Langmuir, Freundlich, and Dubinin-Raduskevich Isotherms and their corresponding constants were calculated. Ho and So were calculated from the slope and intercept of plots of lnKD vs. 1/T. Go values decreases with increasing temperature, showing that the adsorption of Ce(III) is more favorable at high temperature. The endothermacity of the adsorption process is discussed.

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Abstract  

Thermodynamic treatment of the experimental data on the extraction of quadrivalent Pu, U, Th and Zr with tri-n-butyl phosphate (TBP) from nitric acid solutions is presented. It is shown that the extraction of all the quadrivalent metals studied is going according to the same mechanism: M(OH)4−i+(4−i)NO 3 +2TBP⇌M(OH)i(NO3)4−i·2 TBP. For Zr, i=0, 1, and 2; for the remaining M(IV), i=0 and 1. The thermodynamic constants of extraction of M(IV) with the kerosene solutions of TBP according to the above mentioned equation are as follows: Zr: K 0 0 =0.6; K 1 0 =14; K 2 0 =5. Pu: K 0 0 =380; K 1 0 =4.8·104. U: K 0 0 =300; K 1 0 =1.8·104. Th: K 0 0 ∼150. It has been established that Zr and Pu(IV) are extracted into 2-thenoyltrifluoracetone (HA) from perchloric acid solutions under the formation of MA4 and M(ClO4)A3 species. For the extraction from nitric acid solutions, the species formed are ZrA4 and Zr(NO3)A3 in the case of Zr, PuA4 and Pu(OH)A3 in the case of Pu. The differences in the qualitative and quantitative characteristics of the extraction of M(IV) with TBP and HA from nitric and perchloric acids are explained by the effect of the character of the acid and of ionic potential upon the structure of the hydration shell of M aq 4+ .

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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 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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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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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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