Four Bi-Sb alloys with compositions Bi79.6Sb20.4, Bi56.9Sb43.1, Bi39.8Sb60.2, Bi18.6Sb81.4 have been investigated regarding the microstructures and thermal properties. The microstructure was examined ...by scanning electron microscopy with energy-dispersive X-ray spectrometry. The light flash method was applied to determine thermal diffusivity and to obtain thermal conductivity in the temperature range 25 to 150??, while the indirect Archimedean method was used for determination of densities of the investigated Bi-Sb alloys. The obtained results have shown that the density of the studied alloys decreased monotonically with increasing the antimony content. On the other hand, the specific heat capacity of Bi-Sb alloys increased with the increase in the antimony content as well as with increasing the temperature. Thermal diffusivity of the alloys increased slightly with increasing the temperature. Thermal conductivities of the examined Bi-Sb alloys were determined to be in the range of 3.8 to 7 W m-1 K-1, which is lower than thermal conductivities of pure bismuth and antimony. The results obtained in this work represent a contribution to better knowledge of the thermal properties of Bi-Sb alloys, which are of key importance for determining the possibility of their practical application.
In this work the ternary Cu-Ge-In system has been experimentally examined and analytically studied by using the CALPHAD method. The Cu-Ge-In system is interesting due to the possible application in ...the electro industry and since phase equilibria of the ternary Cu-Ge-In are unknown. Three vertical sections Cu-GeIn, Ge-CuIn and In-CuGe were experimentally investigated by using differential thermal analysis (DTA) and experimental results were compared with predicted corresponding vertical sections. Nine samples were annealed at 300 °C and 200 °C and analyzed using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS). EDS results were compared with calculated isothermal sections at 300 °C and 200 °C. According to the comparison of experimental results and calculated phase diagram, good agreement has been achieved. Liquidus projection, invariant reaction and scheme of invariant reaction are presented. Scheil and Lever simulation of solid phases for Cu
80
Ge
10
In
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alloy were calculated.
Lead-free solders have become a main focus of the electronic industry in recent years, because of the high toxicity of lead. Alloys based on the Sn-Bi system figure as potential replacements for ...Sn-Pb alloys in soldering due to favorable properties and low cost. One of the main advantages of these alloys are low melting temperatures, while additional advantages include good compatibility with substrates, low process temperature, high reliability, and potential applications in conjunction with reduced graphene oxide nanosheets as thermal interface materials. In this paper, characterization of microstructural and thermal properties as well as hardness measurements of seven alloys of different Sn-Bi compositions are performed. Structural properties of the samples were analyzed using optical microscopy and scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS). Thermal conductivity of the samples was investigated using the xenon-flash method, and phase transition temperatures were measured using the differential scanning calorimetry (DSC) analysis.
The calculated results of thermodynamic properties in ternary Au-Ga-Sb system by general solution model were presented in this paper.The calculations were carried out in nine cross sections from all ...three corners in the temperature range of 973–1,573 K,and integral molar excess Gibbs energies,partial molar Gibbs energies,activity coefficients and activities for all components are obtained.The activity of gold and gallium shows negative deviation from Rault＇s law for all investigated sections,while antimony activity is close to the line of ideal conditions and even coincides with the line for high content of antimony in the alloy.Data obtained by calculation were compared with those found in literature.It is concluded that compared values show reasonable good agreement.
In order to better understand why students use Facebook and how Facebook can be used for educational activities students’ attitudes and perceptions towards purposes of Facebook usage and Facebook ...educational usage were investigated in this study. Also, theoretical models of the purposes of Facebook usage and Facebook educational usage proposed in literature were examined using the sample of 226 students from University of Belgrade, Technical faculty in Bor. Previous studies have pointed out that there are three underlying dimensions of purposes of Facebook usage that can be indicated as social relations, work related activities and daily activities. Facebook educational usage also includes three underlying dimensions defined as communication, collaboration and resource/material sharing. These hypothesized three-factor models of purposes of Facebook usage and Facebook educational usage were tested on the present sample data using confirmatory factor analysis. The results confirmed hypothesized latent structures and theoretical validity of both investigated factor models. Further analysis revealed that, according to students, collaboration through academic groups (communities) represents the most important value of Facebook implementation in academic activities.
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•Purposes of usage and educational Facebook usage factor structures were determined.•Purposes of Facebook usage include social relations, work activities and daily activities.•Facebook educational usage includes communication, collaboration and material sharing.•Collaboration through academic groups is the best form of Facebook educational usage.
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•The purpose of this work was to examine students’ attitude toward M-learning.•This paper describes the study of factors that affect the intended behavior of students.•The analysis ...conducted among students on TF in Bor, University of Belgrade.•SEM was applied and tested based on fit index, measurement and structural model.•The most significant influences of using M-learning.
In future, M-learning will no longer be a choice but a necessity in the modern way of learning so that students would be able to keep pace with the times and technology. M-learning has an increasingly significant role in the development of teaching methods of learning in higher education. By using mobile technology, students can easily and quickly access and use learning resources anytime and anywhere. The aim of this paper is to present the results of research in the application of new technologies in higher education with particular emphasis on M-learning as a modern innovative approach. The study was conducted using a survey among students at the Technical Faculty in Bor, University of Belgrade. The proper conclusions were drawn from the data obtained by the survey which had been analyzed by using the appropriate statistical methods in software packages SPSS v. 17 and LISREL v. 8.8.
Este artículo presenta el estudio de las propiedades eléctricas de dos sistemas ternarios basados en antimonio, Bi-Ge-Sb y Al-Cu-Sb. Además de las propiedades eléctricas, en el artículo se presenta ...las microestructuras observadas por microscopía óptica. Se utilizaron cuatro muestras para el análisis de la microestructura utilizando MEB, EDS y DRX. Además, se determinó la microdureza de muestras seleccionadas de la aleación ternaria Bi-Ge-Sb, la dureza se determinó utilizando ensayos Vickers.
•The thermal conductivities of Sn–x at% Zn (x = 69.5, 48.3, 28.1 and 14.1) alloys were determined.•Composition and temperature dependences of the thermal conductivity were obtained.•Phase transition ...temperatures and related heat effects were measured using DSC.•The microstructures of the Sn–Zn alloys were determined.
Four hypereutectic Sn-Zn alloys with 69.5, 48.3, 28.1 and 14.1 at% of Zn were produced by mixing and melting of pure metals Sn and Zn followed by cooling in air to room temperature. Microstructure and chemical compositions of prepared samples were analyzed by using scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry (EDS). It was found that morphology of primary (Zn) phase changes from rounded and equiaxed dendritic structure to plate-like grains and finally to needle-like shape of grains with decreasing Zn content. Formation of characteristic broken-lamellar type of eutectic microstructure was observed in all investigated alloys. Melting behavior of the alloys was studied using differential scanning calorimetry (DSC). Phase transition temperatures and corresponding heat effects were experimentally determined and compared with the results of thermodynamic and phase equilibria calculations using the CALPHAD (CALculation of PHAse Diagrams) method and optimized thermodynamic parameters from literature. Thermal diffusivity of the studied alloys was measured using xenon flash method in the temperature range from 25 to 150 °C. Based on the measured values of thermal diffusivity and calculated specific heat capacity data, thermal conductivities of the solid alloys were obtained. It was found that thermal conductivity decreases monotonously with increasing temperature and Sn content. The results of thermal conductivity measurements were compared with literature data and with the data obtained from the Wiedemann-Franz law and measured electrical conductivities.
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•The aim work was to examine students’ attitude towards FB as virtual classroom.•238 students from the University in Belgrade (Serbia) participated in this study.•SEM (Structural Equation Modeling) ...was applied and tested based on adequate fit index.•Evaluation of measurement models and structural model.•The analysis show that use of Facebook as virtual classroom has a goal for students.•Improving the quality of the education process and widening quantum of knowledge.
Since Facebook is the most popular social network among students, the purpose of this study is to examine the attitude of students towards Facebook as virtual classroom, through consideration of its acceptability level, purpose and education in using. 238 students from the University of Belgrade, Technical Faculty in Bor (Serbia), took part in this study. We used SEM methodology (Structural Equation Modeling), which includes the assessment of the measurement model and on the basis of an adequate fitting indices, the structural model was tested. With the use of current empiric researches, in which sociological facts are interpreted, and conflicting attitudes are cited, this paper shows how students use Facebook in order to improve education.
This paper deals with experimental and analytical investigations of the influence of thermomechanical processing conditions on the mechanical properties and electrical conductivity of PdNi5 alloy, in ...the form of wire ? 0.15 mm, for making catalysts-catchers. Obtained results showed that mechanical properties and electrical conductivity depend on the applied regime of thermomechanical processing. Knowing the dependence of influence of parameters of thermomechanical processing regime on these properties enables the production of PdNi5 alloy with required characteristics for use in the process of catalytic oxidation of ammonia, that is solving problems of loss of platinum metals, especially platinum. The results of analytical investigations of influence of thermomechanical processing regime, by software package SPSS, on tensile strength, elongation and electrical conductivity of PdNi5 alloy in the form of wire ? 0.15 mm showed that using a linear regression model the mutual influences of selected parameters of thermomechanical treatment on mechanical properties and electrical conductivity of PdNi5 alloy, can be adequately described and analyzed. The results showed that tensile strength and electrical conductivity were only slightly affected with a change of temperature and time of annealing while annealing time has significant influence on the elongation value.
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