The temperature dependence of the Gibbs free energy difference (ΔG) between the undercooled liquid and the corresponding equilibrium solid has been analysed for metallic glass forming systems
in the frame of the expression obtained by expanding free energies of the undercooled liquid and solid phases in the form
of Taylor's series expansion. The enthalpy difference (ΔH) and the entropy difference (ΔH) between the undercooled liquid and solid phases have also been analysed. The study is made for five different metallic glass
forming materials, Au77Ge13.6Si9.4, Au53.2Pb27.5Sb19.3, Au81.4Si18.6, Mg85.5Cu14.5 and Mg81.6Ga18.4 and a very good agreement is found between calculated and experimental values of ΔG. The ideal glass transition temperature (Tk) and the residual entropy (ΔSR) of these materials have also been studied due to their important role in assigning the glass formation ability of materials.
Table 5 contain the thermodynamicparameters of association between OH − probe ions and dissipative structures in the EDS.
Thermodynamicparameters for the association between EDS and OH − ions, at 298 K
Authors:Renu Chadha, Poonam Arora, Sushma Gupta and Dharamvir Singh Jain
equation is given in Eq. 7 :
Putting Eq. 7 in Eq. 4 ,
The best fit values of the thermodynamicparameters K and ΔH were determined by our computer program utilizing an iterative non-linear least square regression method to
Authors:R. Donat, G. Cılgı, S. Aytas and H. Cetisli
This paper discusses the sorption properties for U(VI) by alginate coated CaSO4·2H2O sepiolite and calcined diatomite earth (Kieselguhr) (ACSD). The removal of U(VI) from aqueous solution by sorption onto
ACSF in a single component system with various contact times, pH, temperatures, and initial concentrations of U(VI) was investigated.
The sorption patterns of uranium on the composite adsorbent followed the Langmuir, Freundlich and Dubinin-Radushkhevic (D-R)
isotherms. The Freundlich, Langmuir, and D-R models have been applied and the data correlated well with Freundlich model and
that the sorption was physical in nature (sorption energy, Ea = 17.05 kJ/mol). The thermodynamic parameters such as variation of enthalpy ΔH, variation of entropy ΔS and variation of Gibbs free energy ΔG were calculated from the slope and intercept of lnK0 vs. 1/T plots. Thermodynamic parameters (ΔHads = 31.83 kJ/mol, ΔSads = 167 J/mol·K, ΔGoads (293.15 K) = −17.94 kJ/mol) showed the endothermic heat of sorption and the feasibility of the process. The thermodynamics
of U(VI) ion/ACSD system indicates the spontaneous and endothermic nature of the process. It was noted that an increase in
temperature resulted in a higher uranium loading per unit weight of the adsorbent.
The melting temperature of nine piperidinoethyl esters of alkoxyphenylcarbamic acid (hexaoxy-octyloxy) including all site
isomers was investigated. The analyses were performed using DSC apparatus, sample mass ranged from 0.2 to 2.5 mg, heating
rate was 5 K min-1 and in static air atmosphere. On the basis of melting peak, thermodynamic figures like: enthalpy, entropy, height and area
of the peak and temperature of the partial peak were fixed. For evaluation of the results Principal Component Analysis was
applied. Thanks to this method the influence of length (mass) and position of alkoxy substituents on the thermodynamic parameters
of melting of compounds under investigation were determined.
In this research, a new composite, poly (hydroxyethylmethacrylate-hydroxyapatite) [P(HEMA-Hap)], was synthesized and its adsorptive
features for natural radionuclides (TI+, Ra2+, Bi3+and Ac3+ in a leaching solution) were investigated at differing initial pH, concentration and temperature ranges. The natural radionuclides
were counted by gamma spectrometer using a type NAI (Tl) detector. The adsorption data obtained were well represented by Langmuir
and Freundlich type isotherms. The magnitude of determined monolayer adsorption capacities (XL) for the adsorbed radionuclides were TI+ = Ac3+ > Ra2+ = Bi3+. These results demonstrated that P(HEMA-Hap) had high affinity to the natural radionuclide. The thermodynamic parameters
indicated that the adsorption mechanisms were spontaneous (ΔG < 0) in terms of adsorption free enthalpy, and changes in the enthalpy and entropy values showed that the overall adsorption
process was endothermic (ΔH > 0), thus increasing entropy (ΔS > 0).
The uranium(VI) biosorption by grapefruit peel was studied from aqueous solutions. Batch experiments was conducted to evaluate
the effect of contact time, initial uranium(VI) concentration, initial pH, adsorbent dose, salt concentration and temperature.
The equilibrium process was well described by the Langmuir, Redlich–Peterson and Koble–Corrigan isotherm models, with maximum
sorption capacity of 140.79 mg g−1 at 298 K. The pseudo second order model and Elovish model adequately describe the kinetic data in comparison to the pseudo
first order model and the process involving rate-controlling step is much complex involving both boundary layer and intra-particle
diffusion processes. The effective diffusion parameter Di and Df values were estimated at different initial concentration and the average values were determined to be 1.167 × 10−7 and 4.078 × 10−8 cm2 s−1. Thermodynamic parameters showed that the biosorption of uranium(VI) onto grapefruit peel biomass was feasible, spontaneous
and endothermic under studied conditions. The physical and chemical properties of the adsorbent were determined by SEM, TG-DSC,
XRD and elemental analysis and the nature of biomass–uranium (VI) interactions was evaluated by FTIR analysis, which showed
the participation of COOH, OH and NH2 groups in the biosorption process. Adsorbents could be regenerated using 0.05 mol L−1 HCl solution at least three cycles, with up to 80% recovery. Thus, the biomass used in this work proved to be effective materials
for the treatment of uranium (VI) bearing aqueous solutions.
Potentiometric studies on Schiff bases derived from5,7-dihydroxy-6-formyl-2-methylbenzopyran- 4-one were carried out at different
ionic strengths (0.02, 0.04, 0.06, 0.10 and 0.14 M NaCl), at different temperatures (25, 35, 45 and55C) and in ethanol-water
media of varying compositions (60, 70, 80 and 90% v/v). The ionization constants of the Schiff bases were investigated in
the presence of different organic solvents (70% v/v), e.g. methanol, ethanol, n-propanol, isopropanol, acetone, DMSO and DMF-water
media. The thermodynamic parameters (ΔG, ΔH and ΔS) were also calculated.
The adsorption studies of Eu(III) was investigated on 2-thenoyltrifluoroacetone (HTTA) loaded PUR foam. The adsorption conditions were optimized with respect to pH, shaking time, loading capacity and adsorbent weight. The adsorption data followed the classical Freundlich and Langmuir type isotherms successfully. The Freundlich constant (1/n) is estimated to be 0.35±0.02, reflects a surface heterogeneity of the PUR foam. Langmuir isotherm gives a saturated capacity of 0.082±0.002 mmol.g-1 suggests a monolayer coverage of the surface. The Dubinin-Radushkevich (D-R) isotherm is applied and the sorption mean free energy (E) is calculated and found to be 13.36±0.12 kJ.mol-1 suggesting that chemisorption involving chemical bonding is responsible for the adsorption process. The thermodynamic parameters such as enthalpy (H), entropy (S) and Gibbs free energy (G) were calculated and interpreted. The positive value of H indicates that the adsorption of metal ions on HTTA-loaded PUR foam is an endothermic process. A possible explanation of this endothermicity has been given. The selectivity and sensitivity of the adsorbent was also studied. The sorption of Eu(III) is greatly affected in the presence of oxalate and fluoride. The sorptive affinity of different cations towards HTTA loaded PUR foam was also discussed.