Phase diagrams for the systems AgCl-CoCl2 and AgBr-CoBr2 were determined by differential scanning calorimetry. The systems are of the eutectic type. Eutectic points are at 271±2
K, 19.5 mol% CoCl2 and 653±2 K, 17.0 mol% CoBr2, respectively. The solid solubility does not exceed 2 and 4 mol% in the systems AgCl-CoCl2 and AgBr-CoBr2, respectively. Thermodynamic activities of components in molten mixtures and molar free enthalpies of mixing were determined
for both systems on the basis of liquidus curves. Deviations from ideality were not found to be considerable.
Authors:Alina Wojakowska, Stanisława Plińska, and E. Krzyżak
A solid-state phase transition in cobalt dibromide at 647 K has been revealed by three different alternative current techniques.
A small thermal effect of (181±18) J mol−1 corresponding to the enthalpy of the transition has been determined by differential scanning calorimetry. The effect was
observed on cooling and on heating as well.
Authors:Alina Wojakowska, E. Krzyżak, and Stanisława Plińska
and high temperature solid-state transitions in CoCl2
and CoBr2 are widely discussed. On the basis of DSC
and conductometric measurements it was found that melting process of CoCl2
is preceded by a solid-state transition appearing about 20 K below the melting
point of CoCl2. Due to deconvolution of the thermograms,
the enthalpy of fusion and that of solid-state transition were found to be
36.4 and 9.6 kJ mol–1, respectively. Melting
points of CoCl2 and CoBr2 were
established to be 999.0 and 949.7 K, respectively. Hitherto unknown enthalpy
of fusion of CoBr2 was determined to be 27.2 kJ mol–1.
A solid-state transition in CoBr2 at 650 K has been
Authors:Edward Krzyżak, Alina Wojakowska, Andrzej Wojakowski, and Marek Wołcyrz
Phase diagram for the system CuBr–LiBr was determined by differential scanning calorimetry and X-ray powder diffraction. The
system exhibits a significant solid solubility of the components, especially LiBr in the respective polymorphic modifications
of CuBr. Another feature of the system CuBr–LiBr is the occurrence of five invariant three-phase equilibria, which have been
assigned to one eutectic (684 K), one peritectoid (668 K), and three eutectoids (679, 645, and 521 K). From the experimental
results, formation of a compound LiCuBr2, at 521 K is discerned.
Authors:Agata Górniak, Alina Wojakowska, Stanisława Plińska, and E. Krzyżak
Electrical conductivity of solid systems AgX-MX2 (where M=Cd, Co, Zn and X=Cl, Br) were measured in a large range of temperature and compositions. Activation energies and conductivity values vs. composition are presented and discussed in relation to phase equilibria in the respective systems. Maximum of the conductivity
value and stabilization of the activation energy have been found for silver halides doped heavily with divalent cation e.g.
in the systems forming solid solutions on the silver halide side. Disorder in AgBr on the approach to melting, expected to
be higher than in AgCl, has been shown by means of original DSC curves presented for both halides.
Authors:Agata Górniak, Alina Wojakowska, Bożena Karolewicz, and Janusz Pluta
Enhancement of the dissolution rate of poorly soluble compounds through the formation of drug–drug eutectics was investigated using fenofibrate and acetylsalicylic acid. Solid–liquid equilibria in the system under study were investigated by differential scanning calorimetry (DSC). The phase diagram for the whole range of compositions was constructed. In addition, existence of a metastable polymorph of fenofibrate has been confirmed. The investigation has revealed that acetylsalicylic acid and fenofibrate form a simple eutectic mixture containing 0.958 mol fraction of fenofibrate at the eutectic point. Dissolution rate improvement of fenofibrate correlated with the phase diagram. The amount of fenofibrate released from the solid dispersions that contained fenofibrate as the eutectic mixture with acetylsalicylic acid was at least threefold higher compared to untreated fenofibrate.