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Kaptay G.,Applied NanoMaterials | Kaptay G.,University of Miskolc
Calphad: Computer Coupling of Phase Diagrams and Thermochemistry | Year: 2014

In this paper the performance of the linear, exponential and combined models to describe the temperature dependence of the excess Gibbs energy of solutions in the framework of the Redlich-Kister model is discussed. The models are not compared to existing Calphad optimized databases, rather they are tested against the 209 binary solid and liquid metallic alloys, for which reliable experimental data exist on the heat of mixing and Gibbs energy of mixing in the handbook of Predel. It was found that the linear model often leads to high-T artifact (artificial inverted miscibility gaps) and the excess Gibbs energy approaches infinity at high temperatures, which seems unreasonable. It was also found that although both the exponential and combined models can in principle lead to low-T artifact (liquid re-stabilization), in real systems it probably does not take place, at least for the "normal" systems (a system is "normal", if the heat of mixing, excess entropy of mixing and excess Gibbs energy of mixing have the same sign at the temperature of measurement; 86% of all systems are found "normal"). The problem with the exponential model is that it is unable to describe the "exceptional" systems (14% of all systems). It is shown that the combined model is able to describe also these "exceptional" systems, as well. An algorithm is worked out to ensure that the combined model does not run into any high-T or low-T artifact, even when it is used to describe the "exceptional" systems. It is concluded that the T-dependence of the interaction energies for all solution phases described by the Redlich-Kister polynomials should be described by the combined model. In this way an improved databank on excess Gibbs energies of solution phases can be gradually built, not leading to any artifact. © 2013 Elsevier Ltd. Source


Larbi A.,National Engineering School of Tunis | Dahman H.,Applied NanoMaterials | Kanzari M.,National Engineering School of Tunis | Kanzari M.,University of Tunis
Vacuum | Year: 2014

In this paper we present the influence of substrate temperature on structural and optical characteristics of the ternary Sn3Sb 2S6. The samples were deposited by vacuum thermal evaporation onto glass substrates at various substrate temperatures (30-60-100-140-160) °C. The films were analyzed by X-ray diffraction, atomic force microscopy (AFM) and spectrophotometric measurements. The XRD analysis showed the presence of only homogenous Sn3Sb2S6 phase. The surface roughness of the deposited films varied between 3.6 and 16 nm with decreasing the substrate temperature from 160 to 30°C. We found that by increasing the substrate temperature from 30 to 160°C, the optical band gap decreased from 1.47 to 1.18 eV. The absorption coefficients of the films are in the range of 105-106 cm-1. The refractive index n has been analyzed according to the Wemple-Di Domenico single oscillator model and the values of E0 and Ed were determined. © 2014 Elsevier Ltd. All rights reserved. Source


Kaptay G.,Applied NanoMaterials | Kaptay G.,University of Miskolc
Journal of Materials Science | Year: 2012

The abbreviation "nano-Calphad" stands for "Calculation of Phase Diagrams for nano-systems." Nanosystems contain at least one phase or at least one interface layer (film, complexion) with at least one of its dimensions being below 100 nm. The essential task of nano-Calphad is to introduce correctly the surface term into the equation for the Gibbs energy. In view of the controversy between the Kelvin and Gibbs equations, even this task does not have an obvious solution (in the present paper, the Gibbs method is preferred). However, there are many further questions to be addressed when the Calphad method is converted into the nano-Calphad method. This paper attempts to give an as full as possible list of all those problems, such as: (i) the definition of a new, independent thermodynamic variable, (ii) the extended phase rule, (iii) the curvature dependence of the interfacial energies, (iv) the dependence of interfacial energies on the separation between interfaces (including the problem of surface melting), (v) the role of the shapes and relative arrangement of phases, (vi) the role of the substrate (if such exists), and (vii) the role of segregation, taking into account its effect on the mass balance within multi-component nano-phases and its surface phase transition and complexion. It is also shown that the well-known meaning of the tie line in binary two-phase fields is lost in nanosystems. The issues related to the size limits of materials thermodynamics and the need for a more complete databanks on molar volumes and interfacial energies are discussed. © Springer Science+Business Media, LLC 2012. Source


Budai I.,Applied NanoMaterials | Budai I.,Debrecen University
Materialwissenschaft und Werkstofftechnik | Year: 2012

Aluminum matrix monotectic alloys with a homogeneous distribution of the second phase droplets can be obtained in large ingots, if the droplets are stabilized by solid particles of optimized wettability at the interface of the two, immiscible liquid metals. In this paper, Al-matrix emulsions with Cd-rich droplets, stabilized by Al 4Sr intermetallic particles are prepared, based on our previous paper. The new information in the present paper is the development of a new type of a mixer, allowing increased rotational speed, and hence, more efficient emulsification without the danger of mixing the liquid metals out of the crucible. As the comparative experiments proved, the ratio of emulsified Cd-rich liquid was found to increase considerably when the old mixer was replaced by the new one. Particularly, there is no 1-phase Cd-rich sedimentation found at the bottom of the crucible when the mixer of the new design is applied. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Grant
Agency: Department of Defense | Branch: Defense Advanced Research Projects Agency | Program: SBIR | Phase: Phase I | Award Amount: 98.99K | Year: 2009

Precise location control and patterned growth of sub-22 nano meter nano materials have long been central challenges in semiconductor nano material growth, highlighted in the International Technology Roadmap for Semiconductors (2007). We propose to combine a modified optical trapping technology with the metal catalyzed nano material chemical vapor deposition growth system to resolve these challenges. We modify the conventional optical trapping technology to heat the nano metal catalyst particles into liquid droplets and to trap and move these melted droplets towards the center of the trapping laser beam. Then nano materials growth can be catalyzed and initialized in the pre-determined locations precisely. To grow sub-22nm nano materials, we introduce a pre-growth evaporation process to shrink the size of nano metal droplets. We also use time sharing and other parallel trapping techniques for nano material patterned growth with applications to the silicon-germanium material system.

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