Quaternary Phase Equilibrium Research Articles

The modelling of the time-dependency of interfacial properties due to chemical equilibrium reactions in demixed liquid systems

The interfacial properties between demixed liquid phases are of crucial importance in chemical engineering. This holds especially true considering extraction based processes inhabiting a chemical reaction due to the time-dependency of all thermodynamic properties that comes with it. The purpose of this work is to predict the dynamic interfacial properties in the demixed liquid system water + 1-hexanol + hexylacetate + acetic acid, which is overlaid by the auto-catalyzed chemical equilibrium esterification reaction 1-hexanol + acetic acid ↔ hexylacetate + water. In order to predict the interfacial properties for these reactive mixtures as function of time, the incompressible version of the density gradient theory (inc-DGT) was combined to the first time with differential rate equations describing the kinetics of this reaction by activities instead of concentrations. The quaternary phase equilibrium, the reaction kinetics, the reaction equilibrium as well as the inhomogeneous region of the interface were thereby described with an activity coefficient model, namely the NRTL-model. Particular attention is directed to the time-dependency of the interfacial tension while the system strives towards the thermodynamic equilibrium. It could be demonstrated that the prediction of the interfacial tension of the supposed model is very close to experimental data obtained also in this study using spinning-drop tensiometry. Furthermore, the time-dependency of the mole fraction profiles inside the inhomogeneous region of the interface due to a chemical reaction could be made visible for the first time.

Solid-liquid equilibrium for the ternary systems (Na2CO3 + NaCl + H2O) and (Na2CO3 + Na2SO4 + H2O) at 313.15 K and atmospheric pressure

The stable (solid + liquid) phase equilibrium and physico-chemical properties of the ternary systems (Na2CO3 + NaCl + H2O) and (Na2CO3 + Na2SO4 + H2O) at T = 313.15 K have determined by the method of isothermal solution saturation. The solid phases formed in the systems studied were determined by the Schreinemaker wet residue method. According to the experimental data, the phase diagrams and the diagrams of physico-chemical properties versus composition were plotted. It was found that there is one invariant point, two univariant curves and three fields of crystallization in the ternary systems (Na2CO3 + NaCl + H2O) at T = 313.15 K. The three crystallization regions correspond to NaCl (I), Na2CO3·H2O (II), the mixed of (NaCl + Na2CO3·H2O) (III). Field EFUC (IV) corresponds to unsaturated solution. Based on the phase diagrams obtained, we analyzed each invariant point. When Na2CO3 and NaCl were analyzed as (15.80, 17.04) wt%, respectively, the ternary system (Na2CO3 + NaCl + H2O) reached saturation at T = 313.15 K. The phase diagram of the ternary system at 313.15 K includes two invariant points, three invariant curves, and three fields of crystallization of single salts corresponding to Na2CO3, Na2CO3·2Na2SO4, Na2SO4. The two invariant points are cosaturated with two salts, that is (Na2CO3·H2O + Na2CO3·2Na2SO4) and (Na2SO4 + Na2CO3·2Na2SO4), respectively. In the phase diagram of the two ternary systems at 313.15 K, the crystallization region of Na2SO4 was significantly larger than the crystallization region of Na2CO3·H2O and NaCl. The quaternary phase equilibrium in Na+//C1−, CO32−, SO42−-H2O system at 313.15 K was also researched by means the through and intermediate translation techniques together. Thus, knowledge of (solid + liquid) equilibrium, especially the crystalline fields at T = 313.15 K, would be extremely valuable to design and optimize solvent extraction process of Na2SO4 and other crystallization processes involving the two ternary systems in the industrial production.

Quaternary isothermal vapor-liquid equilibrium of the model biofuel 2-butanone + n-heptane + tetrahydrofuran + cyclohexane using Raman spectroscopic characterization

Vapor-liquid equilibrium data of fuel mixtures are of major importance for both fuel production as well as combustion. However, the measurement of vapor-liquid equilibrium data usually requires significant experimental effort. The experimental effort is particularly high if multicomponent mixtures are of interest, as experimental effort rises strongly with a rising number of components. In this work, we efficiently characterize the vapor-liquid equilibrium of a quaternary model biofuel and its binary subsystems. For this purpose, we employ the recently developed milliliter-scale Raman Spectroscopic Phase Equilibrium Characterization (RAMSPEQU)-setup. Vapor pressures are collected at T = 283–333 K, and isothermal pTx-data for mixtures at T = 303.2 K resulting in a pressure range of p = 2.8–81.9 kPa. The PCP-SAFT equation of state is used for thermodynamic modeling. Our binary data agrees well with experimental data from literature. The quaternary phase behavior is predicted with very good accuracy using PCP-SAFT with parameters adjusted to pure substance and binary mixture data only. The milliliter-scale setup allows us to characterize the phase equilibria with just 22 ml (binary) and less than 105 ml (quaternary) of the respective mixtures. The agreement of predicted and experimental quaternary phase equilibrium data indicate the reliability of the employed method for multicomponent vapor-liquid equilibrium measurements.

Effect of tin addition on Nb–Si-based in situ composites. Part I: Structural modifications

This paper reports the effect of adding 2 to 8 at.%Sn on the microstructure of Nb–25Ti–8Hf–2Cr–2Al–16Si. The samples were synthesised by casting and were heat treated for 5 days at 1200 °C. The as-cast and heat-treated microstructures were characterised using X-ray diffraction, scanning electron microscopy and microprobe analysis. The results revealed strong microstructural changes when Sn content exceeded 2 at.% Sn. The two-phase (Nb,Ti)SS/γ-M5Si3 composite evolves towards a quaternary phase equilibrium: (Nb,Ti)SS saturated with Sn/α-M5Si3/(Nb1−xTix)3(Sn1−yTiy)/γ′-M5Si3. The γ′-M5Si3 differs from the γ-M5Si3 through its Hf and Ti contents. The (Nb,Ti)SS fraction decreases strongly, benefitting the (Nb1−xTix)3(Sn1−yTiy) fraction. Therefore, adding greater than 2 at.% Sn addition may dramatically affect the mechanical properties of Nb/Nb5Si3 composites because the solid solution (Nb,Ti)SS has been shown to dominate the toughness of such materials.

Quaternary phase equilibrium of water–carboxylic acid mixture (formic–propionic acid or acetic–propionic acid)–solvent liquid systems at 298.15 K

Liquid–liquid equilibrium data of water–acid mixture (formic–propionic acid or acetic–propionic acid)–solvent (amyl acetate, diisobutyl ketone, and diisopropyl ether) quaternary systems were measured at 298.15 K. Complete phase diagrams were obtained by determining solubility curves and tie-lines. A comparison of the extracting capabilities of the solvents was made with respect to distribution coefficients, separation factors and solvent-free selectivity bases. Reliability of the data was ascertained from Othmer–Tobias plots. It is concluded that the used solvents can be treated as suitable separating agents for dilute aqueous formic–propionic acid or acetic–propionic acid mixtures.

Al-Hf-Nb-Pd (Aluminum-Hafnium-Niobium-Palladium)

For the binary phase diagrams, see [2002Wan] (Al-Hf), [2001Yur] (Al-Pd), [1995Tri] (Hf-Pd) and [Massalski2] for Al-Nb, Hf-Nb, and Nb-Pd systems. The known data on the Al-Hf-Nb and Al-Hf-Pd systems were complied by [1995Vil]. The Al-Nb-Pd and Hf-Nb-Pd systems do not appear to have been investigated. The ternary phase that is of interest in the results reviewed here is the Heusler-type phase Pd2HfAl (L21, AlCu2Mn-type cubic, a = 0.6378 nm). Quaternary Phase Equilibria

Quaternary phase equilibrium diagrams. Representation and interpretation methods

Quaternary phase equilibrium diagrams. Representation and interpretation methods

Phase equilibria in the Si-C-N-O system and the kinetic analysis of silicon carbide whisker growth

The significant binary, ternary and quaternary phase equilibria in the Si-C-N-O system are reviewed particularly with regard to the relative stabilities of α and β forms of silicon carbide and nitride. The standard Gibbs free energies of formation of the relevant high-temperature phases are compared, and for the α-form of SiC and Si3N4 the values are derived from the empirical results. From these free energy values, the phase boundaries in the Si-C-N-O system have been calculated and are plotted as typical RTInPO2 versus 1/T plots. The significance of various phase fields in relation to the processing and fabrication of carbide, nitride and oxynitride ceramics is discussed. The rate of chemical reaction has been analysed and the mechanism of reduction of silica to SiC whisker has been proposed. The energetics of whisker growth is also discussed and the derived value of activation energy is compared with the surface self-diffusivity of carbon in pure β-SiC crystals.

Quaternary Phase Equilibria in the System Zr-N-B-C at 1500°C

Quaternary Phase Equilibria in the System Zr-N-B-C at 1500°C

Quaternary Phase Equilibria in the Ti-Si-N-O System: Stability of Metallization Layers and Prediction of Thin Film Reactions

ABSTRACTDuring high temperature circuit fabrication, metallization layers can come in contact with both solids and gases. Their stability can be addressed with the aid of phase equilibria. Using the Gibbs phase rule as a basis, a method for generating phase diagrams for multicomponent systems can be established. This procedure is described and illustrated by reference to the quaternary phase diagram of Ti-Si-N-O. This phase diagram can then be used to predict stability and/or reactions in metallization layers and thin films.

Solid-state quaternary phase equilibrium diagram for the Hg–Cd–Te–O system

For the Hg–Cd–Te–O system an approximate three-dimensional diagram of quaternary phase equilibrium at room temperature has been constructed for the first time, to aid in the study of Hg1−xCdxTe surface oxides. Thermodynamic calculations based on standard Gibbs energies of formation were performed to determine which phases are mutually stable. Stability relationships were checked by reaction experiments in mixtures of bulk reference compounds, using Raman spectroscopy for analysis. Elemental Hg is shown to coexist in equilibrium with all of the oxide and telluride phases. Thus, it is likely to be present whenever oxidation is incomplete. CdTeO3 is shown to be stable with respect to the other oxides and tellurides. Several instabilities are indicated, in which an oxide can react with the Hg1–xCdxTe to release elemental Hg or Te, or HgTe.