Among nanotechnology-based thermal insulation materials thermodynamic performance of nano-ceramic coatings generates intensive discussions. Complete agreement has not been found yet about the mechanism of their insulating effect. In the Laboratory of Building Materials and Building Physics at Széchenyi István University (Győr, Hungary) heat transfer resistance experiments have been performed in order to describe thermodynamic processes inside nano-ceramic coatings. Previous studies finding after new measurements conducted in 2016-2017 also supported the former assumption that in case of nano-ceramic coatings convective heat transfer coefficient might be taken into account in a different way. Results also showed that thermal insulating effect of nano-ceramic coatings could be caused by a relatively high surface heat transfer resistance.
In this article, the enthalpy of dissolution for oxymatrine in 0.15 M citric acid solution is measured using a RD496-2000 Calvet Microcalorimeter at 36.5 °C under atmospheric pressure. The differential enthalpy (ΔdifHm) and molar enthalpy (ΔsolHm) were determined for oxymatrine dissolution in 0.15 M citric acid solution. On the basis of these experimental data and calculated results, the kinetic equation, half-life, ΔsolHm, ΔsolGm, and ΔsolSm of the dissolution process were also obtained.
Authors:D. Das, P. Pathak, S. Kumar, and V. Manchanda
Sorption behavior of 241Am (~10−9 M) on naturally occurring mineral pyrite (particle size: ≤70 μm) has been studied under varying conditions of pH (2–11),
and ionic strength (0.01–1.0 M (NaClO4)). The effects of humic acid (2 mg/L), other complexing anions (1 × 10−4 M CO32−, SO42−, C2O42− and PO43−), di- and trivalent metal ions (1 × 10−3 M Mg2+, Ca2+ and Nd3+) on sorption behavior of Am3+ at a fixed ionic strength (I = 0.10 M (NaClO4)) have been studied. The sorption of 241Am on pyrite increased with pH from 2.8 (84%) to 8.1 (97%). The sorption of 241Am decreased with ionic strength at low pH values (2 ≤ pH ≤ 4), but was insensitive in the pH range of 4–10, suggesting the
formation of outer-sphere complexes on pyrite surface at lower pH, and inner-sphere complexes at higher pH values. The sorption
of 241Am increased in the presence of (i) humic acid (5 < pH < 7.5), and (ii) C2O42− (2 < pH < 3). By contrast, other complexing anions such as (carbonate, phosphate, and sulphate) showed negligible influence
on 241Am sorption. The presence of Mg2+, Ca2+ ions showed marginal effect on the sorption profile of 241Am; while the presence of Nd3+ ion suppressed its sorption significantly under the conditions of present study. The sorption of 241Am on pyrite decreased with increased temperature indicating an exothermic process.
Authors:N. Smirnova, L. Tsvetkova, B. Lebedev, B. Zavin, and V. Kotov
In an adiabatic vacuum calorimeter the temperature dependence of the heat capacity Cp0 of 1,3,5,7-tetramethyl-1,3,5,7-tetrahydrocyclotetrasiloxane and polymethylhydrosiloxane on its basis was measured between
6 and 350 K mainly with accuracy of about 0.2%. Two-phase transitions corresponding, probably, to the fusion of cis-and trans-conformations of the monomer as well as the glass transition of the polymer were detected. The results obtained were used
to calculate the thermodynamic functions Cp0, H0(T)-H0(0), S0(T), G0(T)-H0(0) of the monomer and polymer in the range from T→0 to T=340 K, and to estimate the zero entropy S0(0) of amorphous polymer. Standard entropies of formation ΔSf0 of the tested monomer and polymer at T=298.15 K as well as the entropy of synthesis of polymethylhydrosiloxane from 1,3,5,7-tetramethyl-1,3,5,7-tetrahydrocyclotetrasiloxane
over the range from T→0 to 340 K were estimated. The value of fractal dimension D in the heat capacity function of the multifractal variant of
the Debye’s theory of heat capacity was found to be 1.5 for polymer in the 18–35 K range, that testifies to its layer-chain
Experimental results on the ΔHsoln of noble gases, polar non-electrolyte molecules, porphyrins, their metallocomplexes and organic electrolytes in individual and mixed solvents are discussed. Xe was shown to indicate changes in solvent mixtures and also to exert a noticeable influence on the character of intermolecular interactions in solutions. The thermodynamic characteristics of the solvation of a series of non-polar and polar molecules are given and their dependence on the solvent nature, composition, isotopy and temperature is shown. For the first time the thermodynamic characteristics of porphyrins and metalloporphyrins in different non-aqueous solvents have been found by direct calorimetry. The possibility of axial coordination of porphyrin metallocomplexes is treated and a method is proposed for estimation of the influence of the functional substituents and the metal atom on the electronic effects in them. Compared to simple inorganic electrolyte solutions, the dependence of ΔHsoln on various factors reveals a specific character.
Authors:J. Błażejowski, K. Krzymiński, P. Storoniak, and J. Rak
The decomposition of the quaternary salts mentioned in the title was examined at the quantum mechanical Hartree-Fock level
of theory employing pseudopotentials combined with a SBKJ** basis set. This enabled identification of intermediate and transition
state species on the reaction pathway and prediction of the thermodynamic and kinetic barriers to the dissociation of the
compounds in the gaseous phase. Application of classical methods permitted the lattice energies of salts, whose crystal structures
had been established earlier, to be predicted. Combination of these latter characteristics with the heats of formation of
gaseous halide ions (available from the literature) and the relevant cations (obtained at the density functional (B 3LYP)/6-31G**level
of theory) provided heats of formation of the salts. On the basis of these values, the thermodynamic and kinetic barriers
to the dissociation of the compounds were predicted. The characteristics thus obtained compare quite well with those available
in the literature or determined in this work on the basis of TG or DSC measurements. These investigations have shed more light
on the mechanism of the thermal dissociation of quaternary salts, and more generally on thermal processes involving solids.
The mixed-ligand complex formation in the system Cu2+−Edta4−−(CH2)6(NH2)2 (L), where L is hexamethylenediamine has been calorimetrically, pH-potentiometrically and spectrophotometrically studied
in aqueous solution at 298.15 K and the ionic strength of I = 0.5 (KNO3). The thermodynamic parameters of formation of the CuEdtaL2−, CuEdtaHL− (CuEdta)2L4− and (CuEdta)2En4− complexes have been determined. The most probable coordination mode for the complexone and the ancillary ligand in the mixed-ligand
complexes was discussed.
A thermogravimetric method was applied to study the hydrogen uptake in the near-β-titanium alloy Ti 10 2 3 and the metastable
β-titanium alloy Ti 21S. The tests were performed in H2-He gas mixtures with various partial pressures of H2 at temperatures between 600 and 800C.
Basic findings such as the decreasing solubility of H2 with increasing temperature could be verified, and first information on the effects of surface conditions was gained. Thus,
it could be shown that, despite the low atomic mass of hydrogen, thermogravimetry is an appropriate tool for investigation
of the H2/metal interactions of titanium alloys.
Crystal structures together with enthalpies and temperatures of fusion of two substituted amino acids, N-acetylsarcosinamide (NASarA) and N-acetyl-L-isoleucinamide (NAIA), were determined by single crystal X-ray analysis and differential scanning calorimetry, respectively. The results were compared with those of some analogous amino acid derivatives previously studied. The detailed knowledge of crystallographic parameters is undoubtedly useful for discussing the thermodynamic results and rationalizing the fusion behaviour, owing to the rather poor knowledge of the molecular interactions occurring in the melt.
Authors:H. Al’tshuler, E. Ostapova, L. Sapozhnikova, and O. Al’tshuler
The thermodynamic characteristics of proton exchange in SO3H groups of a sulfonated network polymer based on cis-tetraphenylmetacyclophanoctol for Na+, Cu2+ cations from aqueous solutions were considered for the first time. Microcalorimetric measurements of the heat effects of
Na+-H+ and Cu2+-H+ exchanges were performed, equilibrium compositions of polymer and solution were determined. The changes of Gibbs energy,
enthalpy and entropy of ion exchange were calculated.