Ternary Peritectic Point Research Articles

Phase relations in the system Na2CO3–CaCO3–MgCO3 at 3 GPa with implications for carbonatite genesis and evolution

The phase relations in the system Na2CO3−CaCO3−MgCO3 have been studied at 3 GPa and 700–1285 °C using a Kawai-type multianvil press. At 700 °C, the system has five intermediate compounds: dolomite, Mg-bearing Na2Ca4(CO3)5 burbankite, Na2Ca3(CO3)4, Na4Ca(CO3)3, and eitelite. As temperature increases to 800 °C, the system is complicated by an appearance of Ca-dolomite and Mg-bearing shortite, while Na2Ca4(CO3)5 disappears. At 850 °C, Na4Ca(CO3)3 decomposes to produce Na carbonate and nyerereite. The latter melts incongruently at 875 ± 25 °C to form Na2Ca3(CO3)4. Incongruent melting of eitelite to magnesite and liquid, occurs at 925 ± 25 °C. Mg-bearing shortite melts incongruently at 950 ± 50 °C, producing Na2Ca3(CO3)4 and liquid. Na2Ca3(CO3)4 disappears at 1000 °C via incongruent melting to calcite and liquid. The liquidus projection of the studied ternary system has seven primary solidification phase regions for magnesite, dolomite-calcite solid solutions, Na2Ca3(CO3)4, Mg-bearing shortite, nyerereite, eitelite, and Na carbonate. The primary solidification regions are separated by five peritectic and three cotectic monovariant lines. The system has six ternary peritectic points and one minimum on the liquidus at 850 °C and 52Na2CO3∙48(Ca0.62Mg0.38)CO3. The minimum point resembles a eutectic controlled by a four-phase reaction, by which, on cooling, a liquid transforms into three solid phases: shortite, Na carbonate, and eitelite. Since the system has a single eutectic at 3 GPa, there is no thermal barrier preventing continuous liquid fractionation from Na-poor toward Na-rich dolomitic compositions more alkaline than eitelite and nyerereite. Considering the present results and previous data, a range of Na-Ca-Mg double carbonates changes in the following sequence upon pressure and temperature increase: Na2Ca2(CO3)3 (Amm2) shortite, Na2Ca(CO3)2 (P21ca) nyerereite, Na2Mg(CO3)2 (R3¯) eitelite (0.1 GPa) → Na2(Ca0.97–0.98Mg0.02–0.03)4(CO3)5 (P63mc), Na2(Ca≥0.91Mg≤0.09)3(CO3)4 (P1n1), Na2(Ca ≥ 0.81 Mg0≤0.19)(CO3)2 (R3¯) nyerereite, Na2(Ca0.77–0.93Mg0.07–0.23)2(CO3)3 (Amm2) shortite, Na4(Ca0.90–0.98Mg0.02–0.10)(CO3)3 (Ia3d), Na2(Mg≥0.9Ca0≤0.1)(CO3)2 (P21ca) eitelite (3 GPa) → Na2(Ca≥0.87Mg0≤0.13)4(CO3)5 (P63mc), Na2(Ca≥0.89Mg≤0.11)3(CO3)4 (P1n1), Na4(Ca ≥ 0.7 Mg0≤0.3)(CO3)3 (Ia3d), Na2(Mg≥0.92Ca0≤0.08)(CO3)2 (P21ca) eitelite (6 GPa). Using the present results at 3 GPa and previous data at 6 GPa in the Na2CO3−CaCO3−MgCO3 system, we constrained isopleths of the Na2CO3 content in melt coexisting with Ca-Mg carbonates. We found that the cratonic geotherms cross the isopleths so that the carbonatite melt percolating upward via the continental mantle lithosphere should become progressively enriched in Na, evolving from alkali-poor dolomitic composition at depths exceeding 200 km toward sodic dolomitic with the ~52 mol% Na2CO3 at 80–120 km depths.

Phase equilibria in the NaF-LiF-LaF3 system

The NaF-LiF-LaF3 system was studied by differential thermal and X-ray powder diffraction analyses. In the system, there are two ternary invariant points, a eutectic (580 ± 2°C, 44.0 mol % NaF, 42.0 mol % LiF, 14.0 mol % LaF3), and a peritectic (595 ± 2°C, 45.0 mol % NaF, 39.0 mol % LiF, 16.0 mol % LaF3). The ternary peritectic point results from the intersection of the crystallization fields of LiF, LaF3, and NaLaF4.

Computational thermodynamic model for the Mg−Al−Y system

The ternary Mg−Al−Y system was thermodynamically modeled based on the optimization of the binary subsystems Mg−Al, Mg−Y, and Al−Y using the CALPHAD approach. Mg−Al data was taken from the COST507 database, whereas the other two binary systems were reoptimized in this work. The liquid phase was described by a Redlich-Kister polynomial model, and the intermediate solid solutions were described by a sublattice model. Ternary interaction parameters were introduced to enable the best representation of the experimental data while considering the occurrence of the ternary compound Al4MgY. The constructed database is used to calculate and predict thermodynamic properties, binary phase diagrams of Al−Y and Mg−Y, and liquidus projections of the ternary Mg−Al−Y. The calculated phase diagrams and the thermodynamic properties are in good agreement with the corresponding experimental data from the literature. Sixteen ternary four-phase-equilibria invariant points were predicted in the Mg−Al−Y system: seven ternary eutectic points, eight ternary quasi peritectic points, and one ternary peritectic point. Further, fifteen three-phase-equilibria in variant points were determined: eight saddle points and seven binary eutectic points.

Study of the Ag–In–Te ternary system: I. Description of the triangle Ag 2Te–In 2Te 3–Te

The phase diagram of the Ag 2Te–In 2Te 3–Te system was studied by DTA, DSC and XRD methods. Three ternary phases are observed in the quasi-binary Ag 2Te–In 2Te 3 section: AgIn 5Te 8, which presents a congruent melting point at 725°C and a solid–solid transition at 699°C, with tetragonal structure for the two varieties; Ag 3In 97Te 147, which presents a cubic structure, melts incongruently at 672°C; AgInTe 2, which crystallizes in a chalcopyrite-type structure at room temperature, undergoes a solid–solid transition at 410/475°C and a binary peritectic decomposition at 650°C. The eutectic valleys are drawn, and the nature and the location of the ternary invariants are given. Eight ternary invariants were found: two ternary eutectics points, five transitory ternary peritectic points and one metatectic point. No liquid–liquid miscibility gap and no glassy region are observed.

Phase diagram of the ternary system CeCl 3–KCl–LiCl

The phase diagram of the ternary system CeCl 3–KCl–LiCl has been investigated by means of differential thermal analysis (DTA). It was found that the ternary system can be subdivided into two pseudoternary systems and no ternary compound was found in the whole ternary system. It was determined that there are six surfaces corresponding to the primary crystallization of KCl, LiCl, CeCl 3, K 3Ce 5Cl 18, K 2CeCl 5 and K 3CeCl 6. There are two ternary eutectic points, E 1 (15.6 wt% KCl, 19.3 wt% LiCl, 65.1 wt% CeCl 3; 395°C) and E 2 (13.6 wt% CeCl 3, 50.8 wt% KCl, 35.6 wt% LiCl; 340°C), and one ternary peritectic point, P (68.1 wt% CeCl 3, 13.5 wt% KCl, 18.4 wt% LiCl; 398°C), in the system CeCl 3–KCl–LiCl.

Phase diagram of SmCl 3PbCl 2MgCl 2

The phase diagram of the rare-earth system SmCl 3PbCl 2MgCl 2 has been investigated by DTA. The results of the ternary system are as follows: four liquidus surfaces corresponding to the primary crystallization of SmCl 3, PbCl 2, MgCl 2 and PbSm 3Cl 11, respectively, five secondary crystallization lines, the ternary eutectic point E = 695 K (25.0 mol% SmCl 3, 57.0 mol% PbCl 2), and the ternary peritectic point P = 713 K (31.5 mol% SmCl 3, 48.0 mol% PbCl 2). The reactions between four equilibrium phases are: L P+SmCl 3⇌PbSm 3Cl 11+MgCl 2 L E⇌PbSm 3Cl 11+PbCl 2+MgCl 2

Phase diagram of the ternary system SmCl 3NaClCaCl 2

The phase diagram of molten salts of the rare earth system SmCl 3NaClCaCl 2 has been investigated by DTA. For four liquidus corresponding to the primary crystallization of SmCl 3, NaCl, CaCl 2 and 2NaCl · SmCl 3, five univariant lines related to the secondary crystallization, ternary eutectic point E = 376°C (33.1 mol% SmCl 3, 46.9 mol% NaCl) and ternary peritectic point P = 389°C (29.3 mol% SmCl 3, 52.6 mol% NaCl) were found.

Phase Diagram of the System LaCl3-CaCl2-NaCl

The phase diagram of ternary system LaCl3-CaCl2-NaCl has been constructed from the phase diagrams of the three binary systems and of thirteen quasi-binary systems determined by DTA. For the binaries LaCl3-CaCl2 and CaCl2-NaCl eutectic points were observed at 651 °C , 35.1 mol% LaCl3 and at 508 °C , 49.9 mol% NaCl, respectively. For LaCl3-NaCl, a peritectic point besides the eutectic point at 545 °C , 36.1 mol% LaCl3 was found at 690 °C , 57.5 mol%, which is attributable to the formation of the peritectic compound 3 LaCl3 · NaCl. The phase diagram of the ternary system has a ternary eutetic point and a ternary peritectic point due to 3 LaCl3-NaCl, the form er at 462 °C and 12.1 - 3 9 .7 - 4 8 .2 mol% (LaCl3-CaCl2-NaCl) and the latter at 612 °C and 26.9 - 55.1 - 18.0 mol%.

Phase Diagram of a Portion of the System Na3AlF6‐AlF3‐Al2O3.

The system Na3AlF6‐AlF3‐Al2O3 was investigated by a combination of quenching, optical microscopy, and X‐ray powder diffraction techniques in order to define liquidus temperatures, univariant lines, and invariant points. Phase fields for the primary crystallization of cryolite, chiolite, aluminum fluoride, α‐alumina, and η‐alumina were located. A ternary peritectic point contained 28.3% AlF3‐4.4% Al2O3‐67.3% Na3AlF6 at 723°C. A eutectic point of composition 37.3% AlF3‐3.2% Al2O3‐59.5% Na3AlF6 occurs at 684°C.

The Orthosilicate‐Iron Oxide Portion of the System CaO‐“FeO”‐SiO2

The phase equilibrium diagram has been determined for the liquidus surface of the portion of the system CaO‐“FeO”‐SiO2 between fayalite, dicalcium silicate, wüstite, and lime. Five ternary peritectic points have been located, but no true eutectics have been found. The primary fields of wuUstite and dicalcium silicate cover most of the area studied (ignoring free iron, which is actually the primary phase in all compositions investigated). The boundaries of smaller fields of olivine solid solution, a parallel‐twinned modification of dicalcium silicate, tri‐calcium silicate, lime, and calciowüstite solid solutions also are delineated. X‐ray data show that lime may contain up to 10%“FeO” in solid solution, whereas wüstite may contain as much as 28% CaO in solid solution. Equilibria involving tricalcium silicate explain earlier observations on open‐hearth slags and furnace‐bottom refractories.