The enthalpies of mixing of ternary liquid Ag-Ca-Ge alloys

Partial and integral enthalpies of mixing of the ternary Ag–Ca–Ge melts were determined for the first time by the high-temperature isoperibolic calorimetry at 1300–1550 K. The experiments were performed for six sections with a constant ratio of two components up to the molar fraction of the third component equal to 0.3. The enthalpies of mixing in this ternary system are exothermic values which increase in absolute value from the Ag corner of the concentration triangle towards the constituent binary Ca–Ge system. The minimum value of the integral enthalpy of mixing was obtained for Ca0.6Ge0.4 composition of the Ca–Ge binary system (about –58.00 kJ mol–1). The enthalpies of mixing of the ternary Ag–Ca–Ge melts are calculated for the whole concentration triangle by the Redlich-Kister-Muggianu method, taking into account the term of specific ternary interaction defined from our experimental data. The topology of the isoenthalpies of mixing is determined.

Enthalpies of mixing in binary Cu–Eu and ternary Al–Cu–Eu liquid alloys

The enthalpies of mixing in liquid alloys of the binary Cu-Eu and ternary Al-Cu-Eu systems were determined over a wide range of compositions by means of isoperibolic calorimetry in the temperature range 1 300 - 1450 K. The enthalpies of mixing in the Cu-Eu system demonstrate small exothermic effects (ΔHmin = -4.1 ± 0.5 kJ · mol-1at xCu = 0.70). The measurements for the liquid ternary Al- Cu-Eu alloys were performed along five sections (xCu/ xEu = 0.70/0.30; 0.50/0.50 and 0.27/0.73 for xAl changed from 0 up to 0.30 and xAl/xEu = 0.20/0.80 and 0.47/0.53 for xCu changed from 0 up to 0.30). The enthalpies of mixing in the ternary system were found to be exothermic and increasing in absolute values from the Al corner towards the Al0.40Cu0.60-Al0.60Eu0.40section and from the constituent binary Cu-Eu system towards the same section. The minimum value of the integral enthalpy of mixing is expected in the vicinity of the Al0.6Eu0.4composition of the binary constituent Al-Eu system (about -23.00 kJ · mol-1).

Moisture sorption isotherm and thermodynamic properties of jamun (Syzygium cumini L.) powder made from jamun pulp and seed

The present work aimed to: i) find the suitable proportion, based on sensory evaluation, of microwave-convective hot air dried jamun (Syzygium cumini L.) pulp and seed kernel powder to be mixed for the preparation of jamun powder (JP); ii) generate and model the moisture sorption isotherm (MSI) of JP; and iii) estimate net isosteric heat of sorption (qst), spreading pressure (φ), net integral enthalpy (Qin), and net integral entropy (Sin). To formulate JP, the proportion (w/w, db) comprising 2% kernel and 98% pulp powder was the most desirable. The Peleg model was the best fit to MSI of JP. The qst decreased following linear relationship from 11.02 kJ. mol-1 at 5% equilibrium moisture content (EMC) to 0.27 kJ. mol-1 at 30% EMC. The φ increased with increase in water activity and decreased with increase in temperature from 25 ºC to 35 ºC, and the values of φ at 45 ºC were even higher than at 25 ºC. Net integral enthalpy (Qin) initially decreased till 6% moisture content in JP and displayed an increasing trend with further increase in moisture content. On the contrary, Sin, kept on decreasing continually with increasing moisture content. The moisture zone of 7-11% was considered safe for storage for storage of JP within the temperature range of 45-25 ºC.

Thermodynamic properties and moisture sorption isotherms of two pharmaceutical compounds

This investigation examines and compares the water sorption isotherms and the thermodynamic properties of two pharmaceutical preparations (Hypril and Azix) intended to be manufactured with the same process plant and equipment. The moisture equilibrium isotherms were determined at 50, 60 and 70 °C using a gravimetric technique. Five isotherm models were explored for their fitting to the experimental data. Azix showed sigmoid type II isotherms while Hypril showed type III isotherms according to the BET classification. All investigated models fitted well the water sorption isotherms of Hypril. By contrast, only GAB and Adam and Shove equations gave appropriate fit to the experimental data of Azix. For both formulations, the isosteric heat and the differential entropy decreased sharply with the increase of equilibrium moisture content to minimum values and thereafter remain constant. In the case of Azix, the integral enthalpy decreased with equilibrium moisture content while the integral entropy increased until reaching a constant value. Contrariwise, Hypril showed decreasing of the integral enthalpy and entropy with the equilibrium moisture content. Keywords: sorption isotherm, enthalpy, entropy, spreading pressure, pharmaceutical formulations

Hydride Formation in the TbNi0.4Co0.6-H2 System

The hydrogenation of TbNi0.4Co0.6 was studied by means of neutron diffraction and calorimetric method with use of the differential heat-conducting Tian-Calvet type calorimeter. It was determined that TbNi0.4Co0.6H3.8 crystallized in orthorhombic CrB-type structure (S.G. Cmcm). The hydride formation is accompanied with strong lattice expansion. In the structure TbNi0.4Co0.6D3.4 deuterium atoms occupy tetrahedral 8f-intersices, trigonal bipyramidal 4c-interstices and octahedral 4b-interstices. Dependence of the differential molar enthalpy of absorption (ΔHabs) vs. the hydrogen concentration in the metallic matrix was obtained at 50°C. It was ascertained that in the range of 0<X<2.0 (X=H/ TbNi0.4Co0.6) ΔHabs =-102.0±2.3 kJ mol-1H2. The value of the integral enthalpy of hydrogen absorption by TbNi0.4Co0.6 equals -99.5kJ mol-1H2 for the composition TbNi0.4Co0.6H3.8.

THERMODYNAMIC PROPERTIES OF WATER DESORPTION OF SOYBEAN BRAN

The differential and integral thermodynamic properties (enthalpy, entropy, Gibbs free energy, temperature isokinetic and spreading pressure) of soybean bran were determined. Experimental data obtained from the literature were adjusted appropriately by GAB equation (R2>0.95), whose parameters were used to estimate the thermodynamic properties of desorption of soybean bran. The differential enthalpy and entropy increased with decreasing equilibrium moisture content and the isokinetic temperature confirmed the linear chemical compensation between the enthalpy and entropy and the process was enthalpy driven. The spreading pressure increased with increasing water activity. The integral enthalpy decreased with increasing equilibrium moisture content, whereas the integral entropy increased, but negative values, reaching up to -0.02 kJ/mol.K.

Analysis of Moisture Desorption Isotherms of Eggplant (Solanum melongena)

Sorption isotherms of eggplant were determined employing, as experimental technique, a static gravimetric method, using saturated salt solutions to achieve the equilibrium. The experiments were carried out at different temperatures (20, 35, 50 and 65 °C). The sorption isotherms can be classified, according to Brunauer’s classification, as type II or III depending on temperature. Equilibrium moisture content data were correlated by two models usually applied to foodstuffs (Brunauer-Emmet-Teller (BET) and Halsey). BET model was employed to determine monolayer moisture content (0.121 kg/kg d.b.). Halsey model was selected by the goodness of fitting. Experimental data were analyzed by a thermodynamic approach to obtain some properties as net isosteric heat, equilibrium heat and differential and net integral entropy. The differential enthalpy and entropy decreased with increasing moisture content and satisfied the compensation theory. The net integral enthalpy and entropy showed maximum values (~31 kJ/mol and ~88 J/mol.K) at 0.093 (kg/kg d.b.) of moisture content.