Simple Eutectics Research Articles

Thermodynamic criterion of separated eutectic phenomena

About 26 kinds of simple and complex binary eutectics were frozen directionally under the condition of electromagnetic stirring. It was found that anomalous eutectics including most metals/non-metals and some metal/intermetallic eutectics, can be separated on macroscopic scale by flow caused by electromagnetic stirring. Moreover, the eutectics in which one of their component phases possess an entropy of solution over 23 J mol-1K-1 showed notable separation. In addition, process factors also affect the formation of a separated eutectic. © 1998 Chapman & Hall

Atomic structure of interface boundaries in liquid metallic eutectic emulsions

It is shown that the concentrations of components in simple metallic eutectics are connected with the composition and the atomic structure of the adsorbed layers, being created under melting on the interface boundaries, inherited from the solid state.

A New Method for Calculating Activities Involving Binary Simple Eutectic Phase Diagrams

A New Method for Calculating Activities Involving Binary Simple Eutectic Phase Diagrams

Thermische analyse binärer systeme von mesogenen cholesterylestern und azoxybenzolen

The binary systems of cholesteryl nonanoate with 4,4′-bis(hexyloxy)azoxybenzene (1) and with 4,4′-bis(heptyloxy)azoxybenzene (2) show induced smecticA phases with transition point maximum. Whereas in (1) the smecticA phase is transformed into the cholesteric phase on heating within the whole range of its existence, in (2) the maximum of the smectic phase is stabilized compared with the cholesteric phase and clears into the isotropic melt directly. The molecular ratio of the maximum is 1∶1 in both cases. Moreover in system (2) a smecticC phase was observed.Cholesterylhexadecanoate forms series of smectic and cholesteric mixed crystals of type I resp. III Roozeboom with cholesteryl nonanoate (3) and with cholesteryl tetradecanoate (4). As the unstable solid modifications of the components become relatively stabilized in some mixtures, additional metastable eutectics are formed, which hardly allow to be transformed into the thermodynamic stable solid crystals. Thus errors happened at previous investigations. In the systems (1) to (3) the solid crystals show simple eutectics, in system (4) mixed crystals type V Roozeboom are formed.

Thermische Analyse binärer Systeme Organischer Verbindungen, die induzierte smektische Phasen bilden

Eight binary systems of a homologous series of cholesteryl esters (from cholesteryl propionate to cholesteryl decanoate) with trans-4-propylcyclohexyl-4-(trans-4-pentyl-cyclohexyl) benzoate (Licristal 1223, Merck, Darmstadt) were examined by thermomicroscopy and DSC analysis. In six cases induced smectic A phases with transition point maxima were observed. The cholesteric resp. nematic phases form continuous series of cholesteric mixed crystals, while the solid phases show simple eutectics.

Design and economic trade‐offs of extractive crystallization processes

AbstractA systematic procedure is formulated for the separation of a binary mixture by means of extractive crystallization. It shous that two flowsheet structures can handle systems with a wide variety of solid‐liquid phase behaviors, including components with simple eutectics, multiple eutectics, and compound formation. Design equations are presented for both flowsheet structures. In addition, design variables and constraints are identified. The economic trade‐offs in extractive crystallization processes are examined through the analysis of an example: the complete separation of paraxylene from meta‐xylene using n‐pentane as the extractive solvent. Comparison of our general methodology with the system‐specific designs reported in the literature shows that the latter are process alternatives of the former.

Some physicochemical studies on binary organic eutectics

Solid-liquid equilibrium data on binary systems of phenanthrene with p-chloronitrobenzene, p-dibromobenzene and diphenyl show the formation of simple eutectics in each case. The linear growth velocity ( v) of pure components and eutectics at different undercoolings (Δ T) obey the Hillig-Turnbull equation v = u(Δ T n where u and n are constants. The observed solidification behaviour of the eutectics is explained by the mechanism proposed by W.C. Winegard, S. Mojka, B.M. Thall and B. Chalmers, Can. J. Chem., 29 (1951) 320. The experimental values for the heat of fusion of eutectics, compared with the theoretical values calculated from the law of mixtures, suggest a cluster formation in the eutectic melt. Using heats of fusion data, excess thermodynamic function, surface energy and critical radius were calculated in order to throw light on the mechanism of solidification and the nature of the interaction between the components forming the eutectic. The microstructural examinations of pure components and eutectics suggest thinly branched eutectic structures resulting from coupled growth of the component phases.

Phase Equilibria and Structural Species in MgF2‐MgO, MgF2‐CaO, and MgF2‐Al2O3 Systems

Partial equilibrium phase diagrams for the systems MgF2‐MgO, MgF2‐CaO, and MgF2‐Al2O3 were determined by differential thermal analysis. Simple eutectics were observed at 8.5 mol% MgO and 1228°± 3°C in the MgF2‐MgO system, at 7.5 mol% CaO and 1208°± 3°C in the MgF2‐CaO system, and at 2.5 mol% Al2O3 and 1250°± 3°C in the MgF2‐Al2O3 system. On the basis of agreements between the activities calculated by the Clausius‐Clapeyron equation and Temkin's model using the present data, the eutectic melt consists of Mg2+, F‐, and O2‐ ions in the MgF2‐MgO system; Mg2+, Ca2+, F‐, and O2‐ ions in the MgF2‐CaO system; and Mg2+, Al3+, F‐, and AlO2¯ ions in the MgF2‐Al2O3 system. Well‐defined long needles of MgO in the MgF2‐MgO system, less defined needles of CaO in the MgF2‐CaO system, and Al2O3 grains in the MgF2‐Al2O3 system were observed by optical microscopy.

Mesomorphic Characteristics of Some New Homologous Series with the Isothiocyanato Terminal Group

Abstract The synthesis is described and the mesomorphic properties have been tested for two homologous series of compounds with the isothiocyanato (-NCS) terminal group: 4-(trans-4′-n-alkylcyclohexyl)isothiocyanatobenzenes (CHBT—formula 1) and 5-trans-n-alkyl-2-(4′-isothiocyanatophenyl)-1,3-dioxans (DBT—formula 2). CHBT are nematics, and reveal low viscosity and low melting points, DBT are A1 smectics. In this work, binary phase diagrams are presented for mixtures of CHBT or DBT with compounds with the —CN terminal group. CHBT and DBT yield with the latter simple eutectics. Moreover, DBT when mixed with A d smectics at an appropriate smectic layer spacing ratio, yield nematic mixtures. The suitability of CHBT as components of display mixtures is postulated.

Utilization of differential scanning calorimetry in the compatibility screening of ibuprofen with the stearate lubricants and construction of phase diagrams

Differential Scanning Calorimetry (DSC) was employed to identify and define the interaction between ibuprofen and stearic acid, stearyl alcohol, calcium stearate and magnesium stearate. All stearates were found to form simple eutectics with ibuprofen, and phase diagrams for each system were constructed.

Theoretical prediction of eutectic temperature and composition

An empirical method for the theoretical prediction of eutectic temperatures and compositions, for binary systems forming simple eutectics, from the reported values of freezing points and fusion enthalpies of the components is described. The eutectic temperatures and compositions thus predicted for systems involving organic compounds are found to be within ±2.5 K and ±0.03 of the experimental values, respectively. However, for binary metal systems this method is of limited success.

Kinetic equation theory of multi-component crystal growth. III. General regularities of binary system crystallization

By two-partition approximation of the distribution function, the growth kinetics is obtained of binary crystals, whose kinetic phase diagrams have the type of a cigar, a cigar with a maximum, a cigar with a minimum, and of simple eutectics. The way is studied in which the shape of the kinetic phase diagrams, the growth rate, the effective distribution coefficients, and other characteristics of the process depend on the microscopic parameters of the model. [Russian Text Ignored].

Interaction of metal layers with polycrystalline Si

Solid-phase reactions of metal films deposited on 0.5-μm-thick polycrystalline layers of Si grown by chemical vapor deposition at 640 °C were investigated by MeV 4He backscattering spectrometry, glancing angle x-ray diffraction, and SEM observations. For the metals Al, Ag, and Au, which form simple eutectics, heat treatment at temperatures below the eutectic results in erosion of the poly-Si layer and growth of Si crystallites in the metal film. Crystallite formation is observed at T≳550 °C for Ag, T ≳400 °C for Al, and T ≳200 °C for Au films. For the metals Pd, Ni, and Cr, heat treatment results in silicide formation. The same initial silicides (Pd2Si, Ni2Si, and CrSi2), are formed at similar temperatures on single-crystal substrates.

ろう付用フラックスの電導度測定結果からみたフラックス作用について

The phase diagram and specific electrical conductivity of fused salt systems ZnCl2-SnCl2, ZnCl2-NH4 Cl and ZnCl2-SnCl2⋅2H2O, which are used generally as flux in soldering, were measured to clear a relation between the structures of these mixed salts and the spread area of Pb-Sn eutectic solder on copper base plate.The results obtained were as follows:1) The diagram of ZnCl2-SnCl⋅2 system is a simple eutectic with no solid solution, and ZnCl2-NH4Cl system forms a intermediate compound formation with two simple eutectics. It seems the diagram of ZnCl2-SnCl2⋅2H2O system is a intermediate compound formation type.2) The dissociation of ZnCl2-SnCl2 system was presumed as follows from the basis of J.D. Mackenzie theory on single zinc-chloride;3ZnCl2→ZnCl64-+2Zn, 2+, SnCl2→Sn22++2Cl-3) Isotherms of specific conductivity of ZnCl2-SnCl2 system deviate negatively from additivity when plotted against composition, and three partial negative deviations were found near the compositions of two eutectics and a intermediate compound in ZnCl2-NH4Cl system at just above liquidus temperature for each.4) The transition temperature obtained from temperature.dependence of activation energy for electrical conductivity of ZnCl2-SnCl2 or ZnCl2-NH4Cl systems coincided with the temperature required for good spreading of the solder on copper plate, using these systems as flux. This result showed that an effective action temperature range of flux is from the liquidus to the transition temperature of itself and, therefore, a recommendable soldering temperature is limitted by these temperatures of flux to be used generally.5) Th flux action of ZnCl2-SnCl2⋅S2H2O system could be explained as follows;SnC-l2⋅2H2O→SnCl2+2H2OZnCl2+H2O→Zn(OH)Cl+HClCuO+2HCl→CuCl2+H2OAlthough two equations of the latter were presented by H.H.Manko, the H2O produced by the dissociation of SnCl2⋅2H2O during heating reacts with ZnCl2 and forms HC1. The HO and SnCl2 act as flux in soldering of the range 180-350°C, and no SnCl2⋅2H2O acts as flux in the form of itself.

Phase Equilibria in the System BaO-SrO-SiO2

Phase equilibria in the system BaO-SrO-SiO2 in air were established using conventional solid-state techniques. The phase relations in the boundary system SrO-SiO2 were completed by determining the liquidus temperatures for the SrO-rich portion of the diagram. The known compounds, SrSiO3, Sr2SiO4, and Sr3SiO3, melted congruently at 1580°±15°, 2325°±15°, and 2170°±15°C, respectively. Simple binary eutectics exist between (1) Sr2SiO4 and Sr3SiO5 at 2150°±15°C and ∼27 mol% SiO2 and (2) Sr3SiO5, and SrO at 2080°±15°C and ∼23 mol% SiO2. All Alkemade lines were established for the ternary system; two of these joins were examined in detail because of extensive solid-solution regions. On the Ba2SiO4-Sr2SiO4 join, a maximum solubility of ∼70 mol% Sr2SiO4 in Ba2SiO4 appears to exist at 2100°±15°C, the eutectic reaction temperature. A two-phase region apparently connects the eutectic reaction isotherm with a high-temperature polymorphic transition (α′±α) of Sr2SiO4. Below this transition temperature, a complete solid-solution series exists between Ba2SiO4 and α′-Sr2SiO4. The BaSiO3-SrSiO3, join contains limited solid-solution regions at the extremities which arise from the solid solubility of 40 mol% SrSiO3 in the high-temperature (β) polymorph of BaSiOs3 and 20 mol% BaSiO3 in SrSiO3 at 1210°±15°C. The only ternary compound isolated, BaSrSi3O8, has a lower limit of stability at 1220°±3°C and melts incongruently at 1275°±3°C.

Systems of niobium monocarbide with transition metals

Phase equilibrium relationships in the pseudobinary systems of niobium monocarbide with iron, chromium, nickel and cobalt have been investigated by metallographic, electron micro-probe and X-ray diffraction techniques. Alloys of variable compositions were arc-melted in an argon atmosphere using non-consumable electrodes and were subsequently annealed at predetermined temperatures, cooled and subjected to various examinations for phase identification. NbC was found to form simple binary eutectics with the respective metals, with partial solid solubility at both ends of the systems. Eutectic compositions and melting points have been determined and phase diagrams indicating solidus and liquidus temperatures and the extent of solid solubility for each system are presented.

The thermodynamics and morphologies of eutectics containing compound phases

Following the successful correlation of eutectic morphologies with the entropies of solution of the constituent phases in simple binary eutectics, the correlation has been extended to include a further 14 systems. In each of these systems, one of the phases is a compound for which the calculation of the entropy of solution must be adapted from the treatment of simple eutectic phases.Based upon the concepts of Hunt and Jackson's eutectic classification, the structures of all the eutectics studied have been shown to correlate well with the calculated entropies of solution. For the more complicated crystal structures of the compound phases, it is not possible to calculate roughness parameters which have the physical significance of those calculated for close packed structures. Thus, although the distinction between non-faceting and faceting behaviour cannot be defined exactly, the structures can be predictably classified by listing in the order of maximum entropies of solution per atom. From such a table the borderline between faceting and non-faceting behaviour is expected at ΔSα ≅ 5.5 cal/g-atom °K.

Binary Phase Diagrams of Some Molecular Compounds—I

Abstract The (i) anthracene-d-camphor, (ii) naphthalene-β-naphthol, (iii) anthracene-hexachlorobenzene and (iv) d-camphor-hexachlorobenzene phase diagrams have been determined by calorimetric measurements, optical microscopy and X-ray diffraction. The effect of the crystal symmetry, molecular volume and molecular shape of the component species on the extent of the terminal solid solutions is considered. In all systems the packing factor between the components is high (>0.92), but only in the case of naphthalene and β-naphthol are the molecules of similar shape. In this system a peritectic horizontal occurs at 367.3 K and extends from 42.5 to 72.5 mole pct β-naphthol, the limits of solubility at 298 K being 57.0 mole pct β-naphthol in naphthalene and 16.5 pct naphthalene in β-naphthol. The other three pairs of compounds form simple eutectics. In the anthracene-d-camphor system a eutectic point occurs at 81.5 mole pct camphor and 400.0 K and the limits of solid solubility at this temperature are 3 mole pct ...

Phase Diagrams for the Systems MgCl2‐MgF2, CaCl2‐MgF2, and NaCl‐MgF2

Equilibrium phase diagrams for the systems MgCl2‐MgF2, CaCl2‐MgF2 and NaCl‐MgF2 were determined by differential thermal analysis, thermal analysis, and temperature‐composition equilibrium techniques. Simple eutectics were observed at 78.0±0.5 mol% MgCl2 and 628°±2°C in the MgCl2‐MgF2 system, at 87.5±0.5 mol% CaCl2 and 694°±2°C in the CaCl2‐MgF2 system, and at 95.5±0.5 mol% NaCl and 786°±3°C in the NaCl‐MgF2 system. The phase diagrams determined for these systems were compared with phase diagrams that were computed using Temkin's model. The phase diagrams of the CaCl2‐MgF2 and NaCl‐MgF2 systems were also compared with diagrams that were computed using the expression suggested by Flood et al. for reciprocal systems. The experimentally determined and computed phase diagrams agreed for the MgCl2‐MgF2 system but not for the CaCl2‐MgF2 and NaCl‐MgF2 systems.

The pseudo binary phase diagrams of PuO 2 with alumina, beryllia and magnesia and the pseudo ternary PuO 2-ThO 2-BeO

The pseudo-binary phase diagrams of plutonium oxide with alumina, beryllia and magnesia have been examined under oxidizing conditions. All three systems are simple eutectics with no intermediate compounds and limited terminal solid solubility. The compositions and temperatures of the eutectics have been determined: the latter are very similar to those reported for the corresponding urania systems. The system BeO-ThO 2 was also found to be a simple eutectic, in agreement with the results of previous workers. In the ternary system BeO-ThO 2-PuO 2, there is negligible solid solubility of beryllia in the plutonia-thoria solid solution and vice versa and a eutectic valley joins the eutectics in the binaries BeO-ThO 2 and BeO-PuO 2.