(K−Na)NO3 and (K−Cs)NO3 phase diagrams were drawn using a simultaneous thermal analysis technique in the range 373 to 623 K. The first phase diagram
shows a minimum freezing equimolar mixture at 494 K, a continuous solid solution in equilibrum with liquid phase and an eutectic
mixture (88 molar % of KNO3) at 380 K.
The second one exhibits an invariant at 400 K corresponding to the KNO3 solid-solid transition, an eutectoid mixture at 10 molar % of KNO3 and 418 K involving the CsNO3 solid-solid transition and an eutectic mixture at 60 molar % of KNO3 and 495 K.
To study the coherence of thermodynamic data of the AgNO3-LiNO3 -RbNO3 ternary system, phase diagram of the binary system AgNO3 -LiNO3 has been obtained between 303 and 550 K by direct and differential thermal analysis technique. This system is characterized
by an eutectic point (25% mol. LiNO3 , 445±1 K) and a plateau due to the solid-solid transition in AgNO3 at 434±1 K. In the solid state the solubility of each component in the other seems to be nil or negligible (no more than
a few percents). Using other thermodynamic data, the excess properties of the binary liquid (AgNO3 - LiNO3 ) were calculated at 623 K.
Phase diagram of the binary system CsNO3–LiNO3 has been drawn by using simultaneously direct and differential thermal analysis between 323 and 723 K. This system is characterized by a congruent intermediate equimolar compound with melting point at 463 K, two eutectic reactions at 447 and 433 K; the eutectic points are respectively at 0,47 and 0,63 mol fraction of LiNO3; a plateau due to the phase transition of CsNO3 at 428 K and an other one at 333 K due to the formation of CsLi(NO3)2. The miscibility in solid state seems to be nil or negligible. These results associated with some other thermodynamic data have been used to calculate the activities of the constituents along the liquidus curve and the activities of the liquid constituents at 723 K. The binary liquid (Cs–Li)NO3 exhibits a negative deviation from the ideal behaviour.
Summary Enthalpy of solution of calcium hydroxyapatite Ca10(PO4)6(OH)2 (CaHap) in hydrochloric and perchloric acid solutions is measured by an isoperibol calorimeter and a C80 microcalorimeter. The former device is adapted to reactions occurring in concentrated acid solutions, whereas the microcalorimeter is suitable for slow processes happening in diluted acid solutions. Some solution mechanisms are suggested for different pH ranges. They are confirmed by complementary solution in the same solvent of the entities produced by the reaction between CaHap and the acid. These entities are CaCl2; Ca(ClO4)2·nH2O; Ca(H2PO4)2 and H3PO4. Extrapolation of solution enthalpies to pH=7 leads to the solution enthalpy of (CaHap) in pure water, which is -406.2 kJ mol-1 from HCl and -437.3 kJ mol-1 from HClO4.
Authors:S. Wacharine, D. Hellali, H. Zamali, J. Rogez, and M. Jemal
The phase transitions of RbNO3 and the binary phase diagram of (Cs,Rb)NO3 were investigated at atmospheric pressure, using simultaneous direct and differential thermal analysis, μDTA and DSC techniques. A fourth phase transition of RbNO3 has been observed at temperature near the melting point. The phase diagram of this system is characterised by a eutectic, two eutectoid and an azeotropic-like invariants. Three limited solid solutions and two continuous solid solutions have been detected at low temperature.
Authors:D. Hellali, H. Zamali, A. Sebaoun, and M. Jemal
The phase diagram of the binary AgNO3–CsNO3 system was constructed using differential thermal analysis (DTA) technique in the range 300–700 K. The apparatus is described briefly. The results exhibit a congruently melting compound CsNO3·AgNO3 (m.p.=453 K) characterized by two allotropic varieties and , an incongruently melting compound AgNO3·CsNO3 (m.p.=450 K) with three forms
, two eutectics (16 mol% CsNO3, 442 K and 32.5 mol% CsNO3, 445 K) and a peritectic (38mol% CsNO3, 450 K). The occurrence of the transitions of intermediates was confirmed by X-ray diffraction at variable temperatures. The phase diagram exhibits also two plateaus at 429 K and 435 K corresponding to the phase transitions of CsNO3 and AgNO3, respectively.