Dragana Zivkovic

Comparison of properties of silver-metal oxide electrical contact materials

Changes in physical properties such as density, porosity, hardness and electrical conductivity of the Ag-SnO2 and Ag-SnO2In2O3 electrical contact materials induced by introduction of metal oxide nanoparticles were investigated. Properties of the obtained silver-metal oxide nanoparticle composites are discussed and presented in comparison to their counterparts with the micro metal oxide particles as well as comparable Ag-SnO2WO3 and Ag-ZnO contact materials. Studied silvermetal oxide composites were produced by powder metallurgy method from very fine pure silver and micro- and nanoparticle metal oxide powders. Very uniform microstructures were obtained for all investigated composites and they exhibited physical properties that are comparable with relevant properties of equivalent commercial silver based electrical contact materials. Both Ag-SnO2 and Ag- SnO2In2O3 composites with metal oxide nanoparticles were found to have lower porosity, higher density and hardness than their respective counterparts which can be attributed to better dispersion hardening i.e. higher degree of dispersion of metal oxide in silver matrix.

THERMODYNAMIC CALCULATIONS IN ALLOYS Ti-Al, Ti-Fe, Al-Fe AND Ti-Al-Fe

Thermodynamic calculations of three binary Ti-based alloys: Ti-Al, Ti-Fe, and Al-Fe, as well as ternary alloy Ti-Al-Fe, is shown in this paper. Thermodynamic calculations involved thermodynamic determination of activities, coefficient of activities, partial and integral values for enthalpies and Gibbs energies of mixing and excess energies at different temperatures: 1873K, 2000K and 2073K, as well as calculated phase diagrams for the investigated binary and ternary systems. The FactSage is used for all thermodynamic calculations.

Thermodynamic study of Ga-Sn and Ga-Zn systems using quantitative differential thermal analysis

The results of quantitative differential thermal analysis application in thermodynamic investigation of two gallium-based binary systems, Ga-Sn and Ga-Zn, are presented in this paper. Integral molar enthalpies of mixing in liquid state, as well as the activities, activity coefficients, and other partial and integral molar quantities were determined at the temperatures of 1000, 1073 and 1200 K (for Ga-Sn system) and 723 K (for Ga-Zn system). Obtained results were compared with literature data and comparison showed good agreement. Also, phase diagrams for the investigated simple eutectic systems were confirmed based on DTA curves and compared with literature.

Thermodynamic and structural analysis of the Pb–InSb system

Abstract Results of thermodynamic and structural analysis of the Pb–InSb system are presented in this paper. Thermodynamic investigations were performed experimentally by Oelsen’s calorimetric method and calculated by thermodynamic predicting according to Chou’s general solution model, while structural analysis of the alloys in Pb–In–Sb system was done by SEM–EDX and diffractometry.

Thermodynamic properties calculation in Ni-Cr-Co liquid alloys using FactSage

The thermodynamic properties of liquid binary and ternary alloys in Ni-Cr-Co system, obtained by FactSage thermodynamic calculations, are presented. Thermodynamic calculations for three binary systems – Ni-Cr, Ni-Co and Cr-Co and ternary Ni-Cr-Co system, involved thermodynamic determination of activities, coefficient of activities, partial and integral values for enthalpies and Gibbs energies of mixing and excess energies at four different temperatures: 2,000 K, 2,173 K, 2,200 K and 2,273 K, as well as calculation of phase diagrams for the investigated binary systems.

Newly developed EMF cell with zirconia solid electrolyte for measurement of low oxygen potentials in liquid Cu-Cr and Cu-Zr alloys

In order to measure the very low oxygen potential by use of stabilized zirconia solid electrolyte emf method, a new cell construction was devised. The idea was based on Janke but a zirconia rod was used instead of the zirconia crucible which contacts liquid alloy electrode. The cell was used for determination of the oxygen potentials in liquid dilute Cu-Cr and Cu-Zr alloys. The reference electrode was Cr,Cr2O3. Emf measurements were performed in the temperature range of 1400-1580K and composition range of 0.198-3.10at%Cr-Cu alloys, and 1380-1465K, 0.085-0.761at%Zr-Cu alloys. The composition of liquid alloys were determined by picking up from the liquid alloys and ICP analysis. By use of the newly devised cell construction in this study, stable emf values were obtained at each temperature and alloy composition. Emf values were corrected by using the parameter for electronic contribution of the YSZ. Activity of Cr obeys Henry’s law and activity coefficient at infinitely dilute alloys of Cr in Cu-Cr alloys are: lng0 Cr =(3.80 at 1423K), (3.57 at 1473K), (3.38 at 1523K) and (3.20 at 1573K). At 1423 K activity coefficient of Zr at infinitely diluted alloy is lnγo Zr = -4.0.

Phase diagram investigation and characterisation of ternary Sn?In?Me (Me = Ag, Cu) lead-free solder systems

The Sn?In?Me (Me = Ag, Cu) systems belong to the group of potential candidates for lead-free solder materials. Samples, representing two vertical sections: with In : Ag = 7 : 3 from Sn?In?Ag ternary system and with Cu : In = 1 : 9 from Sn?In?Cu ternary system, were measured with Differential Scanning Calorimetry (DSC). The experimental transformation temperatures were compared with CALPHAD-type calculation results based on thermodynamic parameter values from COST531 database. The characterisation of investigated samples was done using Scanning Electron Microscopy with Energy Dispersive X-ray (SEM?EDX), Light Optical Microscopy (LOM), electroconductivity and microhardness measurements.

Predicting of the thermodynamic properties for the ternary system Pb−Bi−Mg

R-function method for predicting the ternary thermodynamic properties from its binary ones was applied to the ternary system Pb−Bi−Mg. Activities, activity coefficients, partial and integral molar quantities for Pb, Bi and Mg for the quasibinary sections Pb-X (X=B, C, D, E, F) in the investigated ternary system Pb−Bi−Mg calculated by means ofR-function method are given in this paper. Also, it was determined that results obtained byR-function method reach a good agreement with the experimental results obtained by Oelsen calorimetry.

New evidence for prehistoric copper metallurgy in the vicinity of Bor

– The last three years of archaeological investigations at the site Ru`ana in Banjsko Polje, in the immediate vicinity of Bor, have provided new evidence regarding the role of non-ferrous metallurgy in the economy of the prehistoric communities of north-eastern Serbia. The remains of metallurgical furnaces and a large amount of metallic slags at two neighbouring sites in the mentioned settlement reveal that locations with many installations for the thermal processing of copper ore existed in the Bronze Age. We believe, judging by the finds of material culture, that metallurgical activities in this area also continued into the Iron Age and, possibly, into the 4th century AD.

Experimental Determination fo Ga Activity in Liquid Ga-Sb-Tl Alloys by EMF Method

EMF of galvanic cell with zirconia –based solid electrolytes was measured to determine the activity of Ga in liquid Ga-Sb-Tl alloys between 946 and 1233 K along the tree pseudobinary lines of Ga-(Sb/Tl), (xSb/xTl = 1/3, 1/1 and 3/1) The cell used was: Ga,Ga2O3|(ZrO2)0.92(Y2O3) 0.08|Ga-Sb-Tl, Ga2O3. The activity of Ga (aGa ) was derived by :-3EF = RT ln aGa , where E is cell potential, F is Faraday’s constant, R is gas constant and T is cell temperature. The activity of Ga shows slight negative deviations from ideality in the section with positive deviation from ideality in the whole composition range. The activity of gallium shows slight negative deviations from Raoult’s law in the section with xSb/xTl = 3/1, moderately positive deviations in xSb/xTl =1/1 section and large positive deviations in xSb/xTl =1/3 section.