Thermodynamic and structural investigations of liquid magnesium-thallium alloys

The thermodynamic and microscopic structure of MgTl liquid alloy at 923 K has been studied by using regular associated solution model. The free energy of mixing, heat of mixing, entropy of mixing, activity, concentration fluctuations in long-wavelength limit S_CC(0) and the Warren-Cowley short-range parameter α₁ have been determined. The analysis suggests that this alloy is of a moderately interacting nature. The theoretical analysis reveals that the pairwise interaction energies between the species depend on temperature and there is a tendency of unlike atoms pairing (Mg-Tl) in liquid MgTl alloys at all concentration. The observed asymmetry in the properties of mixing of MgTl alloy in molten state is successfully explained by assuming MgTl complex on the basis of regular associated solution model.     

Thermodynamic investigation of the moderately dilute liquid Bi-Fe-Sb alloys

The molar enthalpies of formation of liquid ternary Bi-Fe-Sb alloys have been determined at 1065 K by direct reaction calorimetry using the drop method. Measurements were performed along two sections: X_Bi/X_Sb = 1/9 and 1/4. The experimental calorimetric data and estimated values with a Redlich-Kister formulation are compared.     

Electrical transport in liquid Sn1-xPbx metallic alloys: a self-consistent approach

The calculations of electrical resistivity of Sn–Pb liquid metallic alloys/solutions are investigated by self-consistent approach. We employ modified empty-core pseudopotential to represent electron–ion interaction, while partial structure factors are calculated using Aschroft–Langreth scheme with hard sphere reference system. The potential parameters for elemental metals were optimised to structural data in our previous paper. Computed results for resistivity as a function of temperature and concentration are discussed with other such results. Overall good agreement confirms the applicability of the present model potential for computing the electrical properties, including thermal conductivity and thermoelectric power for liquid metallic alloys.     

Thermodynamic properties of liquid silver-antimony alloys determined from emf measurements

The thermodynamic properties of the liquid Ag-Sb alloys were determined using solid oxide galvanic cells with zirconia electrolyte. The emfs of the cells:

     

Thermodynamic properties of liquid magnesium-nickel alloys

Summary Magnesium vapor pressures were determined over liquid Mg-Ni alloys for compositionsx _Mg>0.65 using an isopiestic method. Data points between 760 and 890°C were evaluated to derive corresponding partial thermodynamic properties. The composition dependence of the magnesium activities in liquid alloys is shown for a temperature of 1073 K. Additionally, it is possible to obtain the shape of the liquidus curve between about 60 and 70 at% Mg from the results of the isopiestic measurements.

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Thermodynamische Eigenschaften flüssiger Mg-Ni Legierungen

Zusammenfassung Magnesiumdampfdrücke wurden mit Hilfe einer isopiestischen Methode über flüssigen Mg-Ni-Legierungen mit einer Zusammensetzungx _Mg>0.65 bestimmt. Aus experimentellen Punkten zwischen 760 und 890°C wurden die entsprechenden partiellen thermodynamischen Eigenschaften abgeleitet. Es wird die Konzentrationsabhängigkeit der Magnesiumaktivitäten in flüssigen Legierungen bei 1073 K gezeigt. Zusätzlich kann aus dem Ergebnis der isopiestischen Messungen der Verlauf der Liquiduskurve zwischen etwa 60 und 70 At% Mg ermittelt werden.

     

Thermodynamic properties of liquid Cu-Ni-Co-Fe alloys

Data on boundary binary systems in conjunction with geometric models and the Redlich-Kister method were used to calculate the integral thermodynamic characteristics and the activities of the components for liquid Cu-Ni-Co-Fe alloys at 1600°C.     

Thermodynamic properties of liquid zinc-bismuth alloys

Thermodynamic properties of liquid Zn–Bi alloys were investigated between 5 and 95 at % Zn from the liquidus curve to 750°C using anemf method with a molten salt electrolyte. Partial and integral values were calculated and compared with results from the literature. From theemf data the liquidus curve was calculated. The thermodynamic data of the Zn–Bi system are well established and consistent with the phase diagram. The entropies of mixing of various group IIB-VA systems are compared and discussed with respect to compound formation in the liquid state.With 5 Figures     

Thermodynamic properties of liquid bismuth—Lead alloys

On liquid Bi—Pb alloys emf measurements were carried out. From the emf data the thermodynamic properties were calculated. In the temperature range between 643 to 923 K no anomalies in the thermodynamic properties were found. The emf varies linearly with temperature and the activity of Pb shows a slight negative deviation fromRaoult's law. However, when H ^M /x is plotted against (1–x) the results are two staight lines which intersect at approximately 35 at% Bi. This could be interpreted that Bi—Pb melts change from one regular behaviour to another.Herrn Prof. Dr.K. L. Komarek mit den besten Wünschen zum 60. Geburtstag gewidmet.     

Thermodynamic properties of liquid Al-Si and Al-Cu alloys

The partial and integral enthalpies of mixing in liquid Al-Si and Al-Cu alloys were determined by high-temperature isoperibolic calorimetry at 1750±5 and 1590±5, respectively. The thermodynamic properties of Al-Si melts were also studied by electromotive force method in temperature range 950-1270 K. The partial and integral excess Gibbs free energies of mixing in liquid Al-Si and Al-Cu alloys were also calculated from literature data on thermodynamic activity of aluminium. The comparison of our experimental results with literature data has been performed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermodynamic properties of liquid alloys Ni-Eu and Ni-Yb

Mixing enthalpies of melts of the binary Ni-Eu (0 < x _Ni < 0.89) and Ni-Yb (0 < x _Ni < 1) systems at 1300–1750 K were investigated using the isoperibolic calorimetry. They have alternating signs depending on the melt concentration. With the combined analysis of the data determined by us and in literature, the models of the liquid and solid alloys were obtained, and the phase diagrams were calculated.     

Electrical conductivity and thermoelectric power of liquid Co–Sn alloys

The electrical conductivity and thermoelectric power of liquid Co–Sn alloys were investigated in a wide concentration and temperature range. It was shown that the electrical conductivity of the melts decreased with an increase of the Co content. The results are interpreted in the context of the s–d hybridisation model. The corresponding behaviour is caused by sharing electrons from one metal to another one. This is in agreement with the concept of Fermi enthalpy, according to which up to two electrons from Sn transfer to the uppermost bands of Co.     

Electrical transport properties of liquid alloys

Two complementary mechanisms have been proposed for relatively high temperature superconductor MgB₂. While the first is the electron–phonon mechanism of BCS theory, advocated strongly by Pickett and co-workers, the second, by Bianconi et al., invokes Feshbach shape resonances. While we cannot presently discount the second mechanism, and while both proposals exploit the multiband nature of the electronic structure of MgB₂, we show here that five body-centred cubic (bcc) transition metals, whose superconducting transition temperature correlate intimately with elastic constants and therefore are plainly BCS-like in character, lie on a curve which has MgB₂ at the high T _c end. Any alternative mechanism to electron–phonon interaction in MgB₂ will need to account quantitatively for this circumstance.     

Poly(p-xylene disulfide) and poly(p-xylene tetrasulfide): synthesis,cure and investigation of mechanical and thermophysical properties

Abstract

In this work, two polysulfide polymers were synthesized using aromatic organic monomer (α,α′-dichloro-p-xylene) and sodium disulfide (Na₂S₂) and sodium tetrasulfide (Na₂S₄) aqueous monomers. Then, the curing process of the polymers was carried out at 170° C using a rheometer. The structural characteristics of synthesized and cured samples were identified by Raman and Fourier transform infrared (FT-IR) spectroscopies. Also, morphological and thermophysical properties of samples were studied by using the X-ray diffraction (XRD) and differential scanning calorimetry (DSC), respectively. Moreover, the molecular weight of the synthesized samples was determined by proton nuclear magnetic resonance (¹H NMR). Furthermore, the mechanical properties and hardness of the samples were investigated by tensile test and Shore A. The results showed that in the noncured samples during the increase of sulfur in the polymer structure, solubility was increased whereas it decreased the hardness, melting point (T_m ) and glass transition temperature (T_g ) of polymers. But in cured samples, hardness and T_g increase by increasing sulfur and the mechanical properties also improved. This is due to the increase in crosslinks. Also, Tm and solubility are not observed due to the formation of crosslinks.     

Photoacoustic infrared spectroscopy and thermophysical properties of syncrude cokes

This paper presents and interprets photoacoustic (PA) infrared spectra and four different thermophysical properties (thermal conductivity, thermal diffusivity, volumetric specific heat and thermal effusivity) for four sets of hydrocarbon cokes. A total of 12 samples, with varying histories, were analyzed. These cokes are a by-product of the upgrading of bitumen to Syncrude Sweet Blend (a blend of hydrotreated components), and were obtained from several locations in the thermal cokers operated by Syncrude Canada Ltd. in Fort McMurray, Alberta, Canada. PA infrared spectroscopy provides detailed information on the amount and type of residual aromatic hydrocarbons in cokes; aliphatic hydrocarbons are sometimes detected in smaller quantities. Three of the thermophysical properties (thermal conductivity, diffusivity and effusivity) display systematic differences among the cokes. On the other hand, volumetric specific heat hardly varies, a phenomenon that accounts for the observed proportionality between thermal diffusivity and conductivity. Analogous relationships exist between thermal effusivity and both thermal conductivity and thermal diffusivity for these cokes. The magnitudes of these three thermophysical properties tend to increase as aromatics contents, determined by PA spectroscopy, decrease.This revised version was published online in November 2005 with corrections to the Cover Date.     

A Novel Single-pan Scanning Calorimeter. Measurement of thermophysical properties of metallic alloys

In this paper problems associated with a conventional heat-flux DSC are discussed. A single pan calorimeter has been designed and built which eliminates many of the errors that occur in a conventional DSC. It was found that: enthalpy changes and heat capacity were repeatable to better than1%; the apparent latent heat and heat capacity did not depend on specimen size or significantly on rate of heating as often occurs in a two-pan heat-flux DSC; during the melting of pure Al, more than 80% of the latent heat was evolved over a temperature of 0.04 K; in alloys, separate heat capacity peaks for different reaction less than 1 K apart were resolved. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermodynamic properties of liquid Au-Cu-Sn alloys determined from electromotive force measurements

A thermally conductive linear low-density polyethylene (LLDPE) composite with aluminum nitride (AlN) as filler was prepared in a heat press molding. Differential scanning calorimeter results indicated that the AlN filler decreases the degree of crystallinity of LLDPE, and has no obvious influence on the melting temperature of LLDPE. Experimental results demonstrated that the LLDPE composites display a high thermal conductivity of 1.25 W/m K and improved thermal stability at 70 wt% AlN content as compared to pure LLDPE. The dielectric constant and dissipation factor increased with AlN content, however, they still remained at relatively low levels, i.e., <5 in wider frequency range from 10 to 10⁶ Hz. The surface treatment of AlN particles had a beneficial effect on improving the thermal conductivity and dielectric constant, whereas, the dissipation factor was less affected. Additionally, the obtained AlN/LLDPE composites have possessed rather low dielectric constant and high electrical insulation, which is suitable for substrate and packaging materials.     

Thermodynamic properties for binary liquid mixtures of 1-chlorobutane+n-alkanes

Isothermal compressibilities K and isobaric thermal expansion coefficients _p have been measured at 25 and 45°C for pure components and the following binary mixtures: 1-chlorobutane+normal alkanes (n-C_n) where n=6, 8, 10, 12, 14 and 16. With these results and other thermodynamic data from literature the next mixing quantities have also been reported: (V ^E/T)_P, – (V)^E/P)_T, K _S ^v , H ^E/P)_T, (_pVT and C_v. The obtained results have been compared at 25°C with the calculated values by using the Prigogine-Flory-Patterson theory of liquid mixtures. The theory predicts the excess volume V^E and V ^E/P)_T values rather well, the C _P ^E quite poorly, while for V ^E/T)_P and V ^E/P)_T it is only predicted the trend with the chain length of the n-alkane. The last two quantities show deviations between theoretical and experimental, slightly higher in systems with longer n-alkanes than for shorter ones. Our conclusion is that a nonrigid linear molecule, like 1-chlorobutane, has a low ability as a breaker of the pure n-C_n orientation correlations, in between that which we found for toluene and p-xylene and much smaller than for cyclohexane or benzene.     

A comprehensive investigation in determination of nanofluids thermophysical properties

In recent years, research on heat transfer and related equipment has been one of the topics of interest in many different industries. The use of conventional fluids in heat transfer due to their low thermal properties has created problems in this area, so the use of nanofluids in many cases has been a solution to overcome this problem. The parameters affecting the thermophysical and thermal properties of nanofluids are temperature, concentration, size, shape, pH, surfactant and ultrasonic time, among which temperature and concentration have the greatest effect. Existing models and studies in the field of nanofluids are limited to the type of nanoparticles and base fluids and their operating range, and there is no comprehensive model for predicting thermal properties. In the present study, models and theories regarding the determination of thermal conductivity of nanofluids and other thermophysical properties have been comprehensively compiled and the mechanisms for increasing the thermal properties as well as the effective parameters and the effect of each of them on improving the properties are presented. In general, the results showed that thermal properties improve with increasing concentration and temperature. Finally, the role of nanofluids effect on thermal performance in the heat exchangers is studied and the results are summarized.