Thermodynamische und strukturelle Untersuchungen an den Verbindungen der Systeme KCl/MCl₂ (M  Ca, Cd, Co, Ni)

Abstract

Mit einer galvanischen Zelle für feste Elektrolyte wurde die Bildung ternärer Chloride nach der Gleichung nKCl+MCl2=KnMCln+2mit M=Ca, Cd, Co, Ni untersucht. Aus der Abhängigkeit der EMK von der Temperatur wurden neben neben der Gibbs‐Energie für die Feststoffrektionen (ΔGR) auch ΔSR und ΔHRbestimmt. Für die Stabilität der Dopplechloride sind jedoch dei freien Synproportionierungsenthalpien aus den Nachbarverbindungen maßgeblich. Im Falle von RbSrCl3 und RbPbCl3 (nur bei höherer Temperatur stabil) erfolgt die Synproportionierung unter Enthalpieverlust, durch Entropie‐Gewinn kompensiert. Das gleiche gilt für K2CoCl4. Für die Verzerrungsvarianten von KCaCl3 wurde verfeinert (Einkristalldaten).

Thermodynamic evaluation and optimization of the (NaCl+KCl+MgCl2+CaCl2+MnCl2+FeCl2+CoCl2+NiCl2) system

“…No solid solubility was reported and the measured limiting slopes of the KCl and CoCl 2 liquidus curves [47,48] was an artifact [49]. A transition is reported to occur at 125°C [48] or 123°C [49].…”

“…Only the high temperature form of KCoCl 3 is considered in the present calculations owing to the unavailability of relevant thermodynamic data for the low temperature form. The enthalpies of formation from solid KCl and CoCl 2 of K 2 CoCl 4 and KCoCl 3 at T ¼ 298:15 K have been measured by solution calorimetry [49]. The values obtained (which are the same as the values calculated from the present optimization) are ()6.4 and )7.0) kJ Á mol À1 , respectively.…”

“…Using an emf technique, Seifert et al [49] measured the Gibbs free energy changes for the following reactions: • KCl + KCoCl 3 ¼ K 2 CoCl 4 (between 280°C and 345°C), • KCl + CoCl 2 ¼ KCoCl 3 (between 280°C and 345°C). The results are reproduced within the experimental error limits by the present optimization.…”

Di-hydrogen contact induced lattice instabilities and structural dynamics in complex hydride perovskites

“…The minim value of the H ⋅ ⋅ ⋅ H is given for all structural models involved in the transition. The transition sequence of KCa(BH 4 ) 3 is compared to that of the related halide KCaCl 3 [24] on the right. of approximately 5 across the phase transition of KCa(BH 4 ) 3 , from 40 nm in the LT-phase (considered temperature range: 100 to 345 K) to 200 nm in the HT-phase (considered range: 345-500 K).…”

“…In structurally related metal oxides, or halides such as KCaCl 3 [24], CsCaCl 3 [25] or CsSrCl 3 [26], the LT-polymorph subsequently transforms to tetragonal and then cubic symmetry ( figure 1, right). The pre-transition behaviour of KCa(BH 4 ) 3 is therefore interesting, as it represents the intuitive temperature evolution of the perovskite lattice.…”