Solidus Curves Research Articles

T(z) diagram and optical energy gap values of Cd1−zMnzGa2Se4 alloys

The T(z) diagram of the system Cd1−zMnzGa2Se4 was obtained from x-ray diffraction and differential thermal analysis measurements. It was found that at lower temperatures, a single phase solid solution occurs across the whole compositional range and values of lattice parameters were determined as a function of z. At higher temperatures, an order-disorder transition occurs, in the range 0 < z < 0.6 to a partially ordered tetragonal structure and for 0.6 < z < 1. 0 to a disordered defect zinc-blende structure. In the T(z) diagram, both the ordering boundary and the solidus curve appear to show discontinuities at z = 0.6, corresponding to the change in the disordered phase. It is suggested that the symmetries of the terminal compounds are different one from the other. Optical absorption measurements were made at 300 K to show the variation of the direct optical energy gap Eo with z, and again the values appear to divide into two parts below the above z = 0.6.

Amphibolite dehydration-melting: sorting out the solidus

Abstract Amphibolite melts under vapour-absent conditions by dehydration-melting, during which H 2 O released from hornblende is transferred directly into H 2 O-undersaturated silicate liquid. Five independent 1991 studies on amphibolite dehydration-melting differ from each other and from earlier conceptual treatments. Five solidi between 7 and 10 kb vary from 975°C to 740°C. Two solidi above 10 kb are near-vertical, near 975°C and 850°C. Some differences are due to different amphibolite compositions and mineralogy. We use the results of earlier experiments involving garnet, supported by our own new results, to construct a closed-system phase diagram for a simple, fully-hydrated amphibolite (hornblende + plagioclase) showing the solidus and the melting interval for (hornblende + garnet + other minerals + liquid). The amphibolite vapour-absent solidus is defined by the beginnings of two multivariant reactions: (1) a near-vertical curve (large positive dP/dT) where the formation of augite dominates; and (2) a near-horizontal curve at higher pressures where the formation of garnet dominates. The solidus curve bends back (estimated near 900°C, 9 kb) with slope changing to low positive dP/dT. The new phase diagram expands the field for liquid generation with garnet-amphibolite residues to much lower temperatures and pressures than the other recent experimental results, increasing the range from which small amounts of hydrous granitoid melts may be segregated by compaction. The reversed, near-horizontal slope of the solidus near 10 kb has interesting petrological consequences.

Miscibility of binary phospholipid mixtures under hydrated and unhydrated conditions. I. Phosphatidic acids with different acyl chain length

The miscibility of binary mixtures of phosphatidic acids (PA) with different acyl chain length ( n = 14, 16 and 18) was examined in the absence of and presence of added water, based on phase diagrams constructed by DSC measurements. The solidus and liquidus curves obtained with unhydrated systems exhibited a minimum isoconcentration point, indicating the non-ideal mixing in both solid and liquid phases. The non-ideality of mixing increased with the chain length difference between the two components. The phase diagrams for hydrated PA mixtures showed a horizontal solidus line, which demonstrates the complete demixing of the two lipid species in solid-gel phase over the whole composition range. In the liquid-crystalline phase of hydrated PA bilayers, the lateral phase separation was suggested by the appearance of a horizontal portion in the liquidus line. The phase diagrams obtained with unhydrated systems were analyzed according to the thermodynamic equations based on the Bragg-Williams approximation. The difference in the mixing behavior was interpreted qualitatively in terms of the pair-interaction in hydrated and unhydrated mixtures.

Solidus reactions in synthetic lherzolite-H 2O-CO 2 from 20–30 kbar, with applications to melting and metasomatism

Mixtures of synthetic forsterite, enstatite, diopside and natural dolomite were used to determine solidus reactions for synthetic lherzolite-H 2O (passing through 1125, 1060 and 1005°C, at 10, 20 and 30 kbar, respectively), and dolomite-lherzolite with mixed vapor, two curves not previously located experimentally. The vapor-buffered curve for dolomite-lherzolite has a distinctive pressure minimum, passing down from the CO 2 system near 28 kbar and 1230°C to a minimum near 22 kbar and 1975°C, with decreasing CO 2/H 2O in the vapor, and then up in pressure through a point at 30 kbar and 990°C. These new results, together with published results in other parts of the system, permit complete construction of the three divariant solidus and decarbonation surfaces meeting along the vapor-buffered dolomite-lherzolite solidus curve. The vapor phase composition at the pressure minimum on this curve is about 85 mol% CO 2. The corresponding curve for natural peridotites is complicated by the addition of amphibole. The three surfaces define boundaries between regions where various kinds of metasomatic fluids can exist. Their positions are moved to somewhat lower temperatures for natural peridotites, and the significant vapor-buffered solidus ledge occurs within a narrow pressure interval at about 75 km depth. Rapid changes in melt and vapor phase compositions coexisting with peridotite occur within this interval. Shallower than about 75 km, silicate and not carbonatite magmas coexist with peridotite; vapors may range from CO 2 to H 2O. Deeper than about 75 km, near-solidus melts are carbonatitic, with vapor if present being H 2O-rich; CO 2-rich vapors cannot exist. Rising volatile-rich melts (of moderate temperatures) in equilibrium with peridotite must begin to crystallize and give off vapors near this depth, with compositions changing from H 2O- to CO 2-rich as depth decreases. Melts and vapors separate rapidly from crystals at this and greater depths.

Thermodynamic Evaluation of the Nickel‐rich Part of the NiZn‐System

AbstractOptimization of thermodynamic and phase diagram data about the solid and liquid NiZn solutions is performed. The temperature and concentration dependence of the Gibbs free excess energy is described by means of second degree polynomials. The calculated liquidus and solidus curves have been compared to the experimental ones.

25] Parameter estimation in binary mixtures of phospholipids

Publisher Summary This chapter discusses parameter estimation in the binary mixtures of phospholipids. The miscibility of the two phospholipids in the bilayer plane must depend on the lateral lipid–lipid interactions, which, in turn, can be expected to depend on the structural similarity between the component lipids. The structural parameters of phospholipid molecules in the bilayer may change significantly as a function of temperature, particularly around the gel to liquid–crystalline phase transition temperature. The mixing behavior of binary lipid systems may, therefore, be strongly temperature dependent. It is pertinent to mention that the experimental phase diagrams of phospholipid systems are most commonly obtained using high-resolution differential scanning calorimetry (DSC). The aqueous dispersions of binary lipid mixtures of various molar ratios are first incubated extensively at a given low temperature; the lipid samples are then subjected to DSC heating scans at slow scan rate of 10°–15°/hr. The phase transition curves in these DSC scans are used for constructing the solidus and liquidus curves of the phase diagram. The phase diagram is constructed by plotting the onset and completion temperatures, after proper correction for the finite width of the transition peaks of the pure components, as a function of the relative concentration of the higher melting component. The chapter describes a specific application of a program (NONLIN) developed by Michael L. Johnson. The program NONLIN also provides detailed information about relationships among the fitted parameters in the form of covariances, which can also guide the investigator by indicating pairs of parameters that are strongly correlated and may, therefore, be a source of suspicion concerning the validity of the fitting process.

Anomalous mixing of zwitterionic and anionic phospholipids with double-chain cationic amphiphiles in lipid bilayers

High-sensitivity scanning calorimetry has been used to examine the thermotropic behavior of mixtures combining dipalmitoylphosphatidylcholine (DPPC), phosphatidylethanolamine (DPPE) and O-methylphosphatidic acid (DPPA-OMe) with the double-chain cationic amphiphiles N, N-dihexadecyl- N, N-dimethylammonium chloride (DHDAC), 1,2-dipalmitoyloxy-3-(trimethylammonio)propane (DPTAP) and the corresponding monomethylated tertiary amino compounds (DHMMA-H + and DPDAP-H +). At physiological ionic strength, mixtures of these cationic amphiphiles with the anionic phospholipid DPPA-OMe can show gel-to-liquid-crystalline phase transitions at considerably higher temperatures than do either of the pure components. Surprisingly, binary mixtures of DPPC and these cationic amphiphiles also show strongly nonideal mixing, with phase diagrams exhibiting pronounced maxima in their solidus and liquidus curves. Similar behavior is not observed for mixtures of DPPC with DPPA-OMe, which closely resembles DPTAP and DPDAP-H + in backbone configuration and polar headgroup size. The present results suggest that perturbation of the orientation of the phosphophatidylcholine headgroup by cationic amphiphiles, as demonstrated previously by Seelig and co-workers (Biochemistry 28 [1989], 7720–7728), can significantly affect the thermotropic behavior of phospholipids such as DPPC. Such effects may exert a generally important (though not always easily recognizable) influence on the organization and thermotropic behavior of systems where zwitterionic phospholipids are combined with charged bilayer-associated molecules.

Effect of lodide ion substitution on the ionic conductivity and the melting point of NaBr

Ionic conductivity and the phase diagram have been studied for the NaBrNaI system. Maximum conductivity enhancements by factors of 46, 26, and 15 with respect to pure NaBr and 2, 1.8, and 1.4 with respect to pure NaI have been obtained at T = 400, 500, and 600°C, respectively, for the composition of NaBr + 70 mole% NaI. The CBΩ model that predicts the composition of the mixed crystals at which the maximum conductivity occurs was found unsatisfactory for the present system. A new method for constructing the solidus curve of the phase diagram using the conductivity data alone is suggested and found satisfactory for the present NaBrNaI system.

Diffusion in single crystals of melilite: II. Cations

Diffusion coefficients of divalent cations, Ni, Co, Fe, Mn, Ca, Sr, and Ba, in synthetic åkermanite were determined by tracer-diffusion experiments. Diffusion coefficients of cation pairs, Al + Al-Mg + Si, Al + Al-Co + Si, and Mg-Co in melilite solid-solution systems, were determined by coupled annealing of synthetic melilites of endmember compositions. Cobalt tracer diffuses slower along the c- crystallographic axis than along the a- axis by a factor of about three, possibly due to the anisotropic sheet-like arrangement of oxygen ions parallel to the (001) plane which is perpendicular to the c- axis in the crystal structure of melilite. In the coupled diffusion experiments, the cation pairs interdiffuse complementary, as expected for conservation of material and ionic charge balance in the substitution. The tracer-diffusion coefficient of Co in åkermanite agrees well with that obtained by extrapolation of the inter-diffusion coefficient of Mg-Co cation pair to the composition of åkermanite 100-Co · åkermanite 0. This suggests the mechanism of tracer-diffusion of Co in åkermanite is essentially the same as in Mg-Co inter-diffusion. The inter-diffusion coefficients of cation pairs show a strong dependence on the endmember compositions, and can be correlated with the melting temperature or solidus curves in the phase diagrams. The observed trend in the inter-diffusion coefficient vs. melting temperature relations is similar to those observed for alloys and consistent with an empirical rule for self-diffusion coefficient-melting temperature relation. In the diffusion coefficient vs. ionic radius diagram for divalent cation diffusion in åkermanite, smooth curves were observed as in the case of olivine systems. However, the shapes of the curves were significantly different from those observed in olivine systems. The observed trend of diffusion coefficients with ionic radius can be explained on the basis of crystal structure-controlled diffusion in åkermanite. The observed results suggest that Mg diffusivity strongly depends on the chemical compositions of melilite solid-solution series: the estimated diffusivity of Mg in åkermanite is considerably larger than that of O, but is smaller than O in gehlenite.

Phase diagram and enhanced electrical transport in KBr—NaBr mixed crystals

Phase diagram and ionic conductivity of KBr—NaBr mixed crystals system have been studied over the entire composition and stable temperature range. A maximum conductivity enhancement by a factor of 25 with respect to pure KBr, and with respect to pure NaBr, is obtained for the K 0.5Na 0.5Br solid solution at 500°C. The conductivity values are found to follow the melting (solidus) temperature in a correlated manner. The minimum in the solidus curve of the phase diagram is observed between 43 and 72 mole% NaBr at 615°C.

Phase diagram of Zn 2 x(CuIn) yMn 2 zTe 2 alloys

The T versus composition phase diagram of the alloy system Zn 2 x (CuIn) y Mn 2 z Te 2 was investigated in the range 0< z < 0.80 by differential thermal analysis and X-ray diffraction measurements. Samples were prepared for various lines of constant x/ y ratio and the T( z) data determined for each line. From the values of lattice parameter determined for all samples, the limits of single-phase solid solution were estimated. In addition to liquidus and solidus curves, the zinc-blende-chalcopyrite and Mn-disordered-Mn-ordered transition lines were determined, these phase fields being the ones of interest in the measurements of optical energy gap and of magnetic properties.

ChemInform Abstract: Correlations and Alloy Properties: Growth, Vacancies, Surface Segregation

The aspects of bonding interaction mechanisms which have an impact on the correlation state of alloy semiconductors are demonstrated. The effect of the correlation state on liquidus and solidus curves, on surface segregation, and on vacancy densities is deduced. Vacancy energies for several alloys are presented, and tentative conclusions are drawn about their effects on diffusion, doping, and ion beam processing. Features of the theory of surface segregation in semiconductor alloys are then presented.

Phase diagram of Cd 2 x(CuIn) yMn 2 zTe 2 ( x + y + z = 1) alloys

The T vs composition phase diagram of the alloy system Cd 2 x (CuIn) y Mn 2 z Te 2 ( x + y + z = 1) was investigated in the range 0 < z < 0.80 by differential thermal analysis and X-ray diffraction measurements. Samples were prepared for various lines of constant x y ratio and the T( z) data determined for each line. From the values of lattice parameters determined for all samples, the limits of single-phase solid-solution were estimated. In addition to liquidus and solidus curves, the zinc blende-chalcopyrite and Mn-disordered-Mn-ordered transition lines were determined, these phase fields being the ones of interest in the measurements of optical energy gap and magnetic properties.

Phase Relations and the Effects of Ordering in Zn2x ( AgIn ) yMn2zTe2 Alloys

The vs. composition phase diagram of the alloy system was investigated in the range by differential thermal analysis and x‐ray diffraction measurements. Samples were prepared for various lines of constant ratio and the data determined for each line. Values of lattice parameters were determined for all samples and the limits of single‐phase solid solution estimated. In addition to liquidus and solidus curves, the zinc‐blende → chalcopyrite and Mn‐disordered → Mn‐ordered transition lines were determined, these phase fields being the ones of interest in the measurements of optical energy gap and of magnetic properties.

Quasi-quantitative estimation of solidus curve on As-rich side of Ga-As system

A quantitative investigation of the solidus curve on the As-rich side of the Ga-As system was done by estimating the amount of excess As in crystals grown from As-rich melts. Excess As atoms in a GaAs crystal are usually subjected to two forms: precipitation and dissolution. To obtain the solidus curve, it was assumed that the EL2 concentration gives the composition of the crystal when almost all the dissolved excess As form EL2. The maximum EL2 concentration was produced in crystals by a new thermal treatment that dissolves As precipitates and is assumed to change almost all the dissolved As into EL2. The maximum EL2 concentration showed a strong linear correlation with the melt composition. A solidus curve has been drawn that has a parabolic shape similar to the liquids curve. The congruent point is shifted from stoichiometry toward the As-rich side by an amount equivalent to an EL2 concentration of 10 16 cm -3.

Numerical and analytical solutions of one-dimensional freezing of dilute binary alloys with coupled heat and mass transfer

The purpose of the present study is to present simple and effective numerical and analytical solutions of one-dimensional solidification of dilute binary alloys. Although the numerical and analytical results are presented here for one-dimensional radially symmetric inward spherical solidification, the methods of solution are valid for several other one-dimensional problems. It is assumed that the heat and mass transport takes place only by diffusion and there is local thermodynamic equilibrium at the freezing front which is assumed to be planar. In the present study, solidus and liquidas curves are assumed to be linear, however, more general phase diagrams can also be accommodated. Numerical results are presented for wide ranging values of the ratios of diffusivities. The occurrence of steep concentration gradients at the freezing front does not require any special modification of the numerical scheme. Using the present analytical method, all the previously existing exact analytical solutions which pertain only to the semiinfinite region can be derived in a systematic way.

The Na+, K+/CN-, I- binary systems

The phase diagram of the KCN-KI binary system was measured and the published phase diagrams of the KCN-NaCN, NaI-KI and NaCN-NaI systems were verified and completed. The systems form solid solutions with minima on the liquidus and solidus curves. The solid solutions in the KCN-KI system probably have a high segregation temperature, close to the solidus curve. For the four binary systems the experimental points were fitted with liquidus and solidus curves either by applying smoothing spline functions or by using two different models. The results obtained are discussed.

Correlations and alloy properties: Growth, vacancies, surface segregation

The properties of alloy semiconductors are influenced by the state of order of the materials. Some properties, such as the liquidus and solidus curves, are relative insensitive but others are strongly affected. We first demonstrate which aspects of bonding interaction mechanisms impact the correlation state. We then deduce the effect of the correlation state on liquids and solidus curves, on surface segregation, and on vacancy densities. Surface segregation is a concentration variation of the alloy constituents away from surfaces, and is driven by Schottky vacancy-free energy differences between the constituents in the bulk and on a surface. The segregation profile for alloys equilibrated above a critical spinodal transition temperature exhibits a monatomic variation decaying over a few atomic layers from the surface to the bulk value. However, long-range concentration oscillations are predicted below the critical temperature. These oscillations may account for the long-range order observed in some MBE- and MOCVD-grown alloys (e.g., InPSb). The total free energy of this new ordered phase lies between that of a homogeneous but highly correlated alloy and that of a spinodally decomposed alloy. The phase, if it exists, would be locked into its metastable state by the presence of the surface. Boundary conditions at the interface between the epitaxial layer and the substrate would also affect the results.

The solidus of carbonated, fertile peridotite

The solidus for a fertile peridotite composition (“Hawaiian pyrolite”) in the presence of CO 2 has been determined from 14 to 35 kbar. The solidus shape in P-T space is consistent with previous studies in the model system CaO—MgO—SiO 2—CO 2. The intersection of the decarbonation reaction Olivine + Diopside + CO 2 ⇌ Orthopyroxene + Dolomite with the pyrolite solidus defines the point I 6 , which is located at 20.5 kbar, 1050°C. At pressures less than I 6 the solidus is only slightly (20–50°C) below that of the volatile-absent (C—H absent) solidus but at pressures greater than I 6 the solidus curve is approximately 275°C below the volatile-absent solidus. The large depression of the solidus to lower temperatures with little change in pressure occurs at approximately 19 kbar, 1250°C. At 26 kbar the Hawaiian pyrolite-CO 2 solidus is approximately 100°C higher than the solidus for Hawaiian pyrolite-H 2O—CO 2 confirming that the primary sodic dolomitic carbonatite melt at the latter solidus does contain some dissolved water.

The influence of the fluid phase composition on the solidus temperatures in the haplogranite system NaAlSi3O8-KAlSi3O8-SiO2-H2O-CO2

The solidus temperatures in the haplogranite-system NaAlSi3O8-KAlSi3O8-SiO2-H2O-CO2 have been determined up to 15 kbar for a constant molar ratio of sodium to potassium of 1∶1 and for fluid compositions ranging from pure water to pure carbon dioxide. The data for the water-saturated solidus are virtually identical with those of previous studies. At constant pressure, the solidus curve as a function of the fluid phase composition exhibits a point of inflection in the range of the water-rich compositions. This phenomenon is attributed to chemical interactions between the CO2 and the H2O in the silicate melt. The point of inflection disappears if the CO2 in the gas phase is replaced by molecular nitrogen. The CO2-saturated solidi have been measured at 2 and 5 kbars. The data at 5 kbar indicate a melting point depression in the order of 40° C compared to the dry solidus of Huang and Wyllie (1975). The experimental data can be used to estimate the melting temperatures of common quartz and feldspar bearing crustal rocks under the conditions of granulite facies metamorphism. Since for most fluid phase compositions, the solidus curves are very steep in the P, T-diagram, the beginning of melting is nearly exclusively determined by the fluid composition and almost independent of pressure between about 2 and more than 10 kbar. Therefore, the onset of partial melting in quartz and feldspar containing rocks under granulite facies conditions can be used to estimate the composition of a coexisting H2O-CO2 fluid phase if geothermometric data are available. The temperature range between the beginning of granulite facies metamorphism and the initiation of melting expands with increasing carbon dioxide content in the H2O-CO2 fluid phase. At a CO2 molar fraction of 0.9, this range extends from about 600° C to 900° C and is almost independent of pressure.