Search Results
Abstract
Equilibrium adiabatic heat-capacity measurements have been made on zone refined samples of CeB6 and PrB6. Companion measurements made on LaB6, NdB6, and GdB6 have been reported elsewhere. These show cooperative lambda-type anomalies associated with antiferro-magnetic ordering. Except for lanthanum hexaboride, Schottky internal crystal field levels result in significant contributions to the thermodynamic functions. The gross thermodynamic properties at 298.15 K heat capacity (Cp/R), entropy increment (ΔT 0,m S 0/R), and Gibbs energy function are correlated with the nature of the lanthanide. For LaB6, CeB6, PrB6, NdB6, and GdB6 the three properties are, respectively: {11.654, 12.014, 11.997, 11.916, 11.695} Cp/R; {10.001, 11.803, 12.430, 12.558, 13.982} S0/R, and finally {4.379, 5.912, 6.232, 6.451, 7.905}Φ0 m/R.
Abstract
A calorimetric investigation was performed on the partition ofn-pentanol in the external oil phase and in the interfacial layer of the water-in-oil microemulsion system sodium dodecyl-benzenesulfonate(DDBS)/n-pentanol/n-heptane/water. The results show that fine changes can be observed in the structure of the water-in-oil emulsion and microemulsion droplets, such as then-pentanol/DDBS mole ratio increase in the interfacial layer; further, the alcohol/surfactant mole ratio α in the interfacial layer of the droplets, and also the standard thermodynamic functions of the alcohol transition from the external phase to the interfacial phase (ΔG e→s o , ΔH c→s o and ΔS e→s o ), can be derived from calorimetric data.
Abstract
Heat capacity C p(T) of the crystalline dl-cysteine was measured on heating the system from 6 to 309 K by adiabatic calorimetry; thermodynamic functions were calculated based on these data smoothed in the temperature range 6–273.15 K. The values of heat capacity, entropy, and enthalpy at 273.15 K were equal to 142.4, 153.3, and 213.80 J K−1 mol−1, respectively. At about 300 K, a heat capacity peak was observed, which was interpreted as an evidence of a first-order phase transition. The enthalpy and the entropy of the transition are equal, respectively, to 2300 ± 50 and 7.6 ± 0.1 J K−1 mol−1.
Abstract
The solubility and solubility product of europium trifluoride were measured by radiometric, potentiometric and conductometric methods. There are significant differences in the values of both solubility and solubility product obtained by the three different techniques. Due to reasons discussed in the text, radiometric values seem to be more acceptable than the others. The thermodynamic functions such as ΔH0, ΔG0 and ΔS0 for the dissolution process were also measured. The positive values of ΔH0 and ΔG0 and the negative value of ΔS0 are indicative of the slight solubility of EuF3. The dependence of solubility on pH and also on the fluoride concentration has also been studied. It was confirmed that europium forms a monofoluoride complex in aqueous solution. The stability constant of this complex was estimated.
Abstract
Heat capacity measurements between 293 K and 363 K have been carried out in order to elucidate the different states appearing in 2-amino-2-methyl-1,3 propanediol (AMP) plastic crystal. The results allowed one of them to be identified as a glassy crystal. The changes of enthalpy, entropy and Gibbs free energy thermodynamic functions with temperature have been calculated from the experimental heat capacity values.
Abstract
Synthesis and characterization of N,N,N',N'-tetrabutylsuccinamide (TBSA)was carried out and used for the extraction of U(VI) and Th(IV) from nitricacid solutions. Toluene was found to be the most suitable diluent for TBSAcompared with the other diluents tested. Extraction distribution ratios (D)of U(VI) and Th(IV) have been studied as a function of aqueous HNO 3 concentrations,NO3 – ion concentration, TBSA concentration and temperature.The results obtained indicated that U(VI) and Th(IV) are mainly extractedas UO2 (NO3 ) 2 . 2TBSA and Th(NO3 ) 4 . TBSA, respectively, and the IR spectra of the extractedspecies have been investigated. The values of thermodynamic functions havebeen calculated. Back-extraction of U(VI) and Th(IV) from organic phases wasalso studied.
Abstract
Synergic extraction of Eu(III) and Tb(III) with 2-thenoyltrifluoroacetone (HTTA) and tribenzylamine (TBA) as neutral donor ligand has been studied in chloroform from perchlorate media at lower pH range. The stoichiometric composition of the adduct was established as M(TTA)3 · 3TBA for both the elements, having a coordination number 9. The formation constants K3,0 and K3,3 and stability constant 
3,3 of the organic phase reaction have been calculated. The effect of temperature on the extraction has also been studied. The adducts are stabilized by the large exothermic enthalpy change. The calculated thermodynamic functions such as 
H, S and G were used to elucidate the mechanism of synergism in which the coordination numbers of the lanthanide ions increased.
Abstract
The batch kinetics of Fe(III) adsorption on HTTA-loaded polyurethane (PU) foam have been investigated. The rate of controlling the adsorption is found to be intraparticle diffusion. The reaction rate of adsorption and desorption was also evaluated and found to increase and decrease with temperature, respectively. This indicates an endothermic adsorption behavior of Fe(III) on HTTA loaded PU foam. The activation energy of adsorption (80±10 kJ·mol–1) and of desorption (–45±±2 kJ· mol–1) indicates the chemical adsorption rather than physical adsorption. The isosteric heat of adsorption (
H
ads) was found to be –82.7±5.05 kJ·mol–1. This shows the formation of new chemical bonds among Fe(III)-HTTA-PU foam. The thermodynamic parameters of
G,
H and
S, and equilibrium constantK
c have been calculated. These functions further support that the process of adsorption of Fe(III) on HTTA-loaded PU foam is endothermic and chemisorption, stabilized through thermodynamic functions.
Abstract
The non-isothermal kinetics of dehydration of AlPO4·2H2O was studied in dynamic air atmosphere by TG–DTG–DTA at different heating rates. The result implies an important theoretical support for preparing AlPO4. The AlPO4·2H2O decomposes in two step reactions occurring in the range of 80–150 °C. The activation energy of the second dehydration reaction of AlPO4·2H2O as calculated by Kissinger method was found to be 69.68 kJ mol−1, while the Avrami exponent value was 1.49. The results confirmed the elimination of water of crystallization, which related with the crystal growth mechanism. The thermodynamic functions (ΔH*, ΔG* and ΔS*) of the dehydration reaction are calculated by the activated complex theory. These values in the dehydration step showed that it is directly related to the introduction of heat and is non-spontaneous process.
Abstract
Phases may be smaller than visible to the human eye. In order to characterize a microphase, a phase smaller than 1 μm, one must consider surface area and free energy in addition to the standard thermodynamic functions. As one approaches nanometer sizes, one also needs to know the changing thermodynamic functions within the phases. The Gibbs–Thomson equation can be used to characterize microphases, but not nanophases. For the latter, the glass transition is needed to assess the properties in the interior. In order to classify condensed phases as liquid, solid, mesophase, or crystal, one needs to consider the molecular motion in addition to the molecular structure. Most important are large-amplitude displacements in form of translation, rotation, and conformational motion. An operational definition based on experiments and an updated classification of the phases is given. The surprising result is the observation that crystals, earlier assumed prime examples of solids, can have order–disorder transitions to more mobile mesophases, as well as a glass transition without change in crystal structure, i.e., under certain condition, they cannot be identified as a solid. To these observations, one has to add the fact that large-amplitude motion may start gradually to a more mobile phase without abrupt changes in structure. These observations limit the usefulness of the 80-year-old classification of transitions as being of first or second order. Quantitative thermal analysis is shown to be an important tool to identify the possible total of 57 different condensed states in terms of their macroscopic properties as well as molecular structure and motion.
