Search

In the present work, the microstructure, phase constitution, and corrosion behavior of binary Sn–xZn alloys (x = 5, 9 and 15 wt.%) were investigated. The alloys were prepared by induction melting of Sn and Zn lumps in argon. After melting, the alloys were solidified to form cast cylinders. The Sn–9Zn alloy had a eutectic microstructure. The Sn–5Zn and Sn–15Zn alloys were composed of dendritic (Sn) or (Zn) and eutectic. The corrosion behavior of the Sn–Zn alloys was studied in aqueous HCl (1 wt.%) and NaCl (3.5 wt.%) solutions at room temperature. Corrosion potentials and corrosion rates in HCl were significantly higher compared to NaCl. The corrosion of the binary Sn–Zn alloys was found to take place by a galvanic mechanism. The chemical composition of the corrosion products formed on the Sn–Zn alloys changed with the Zn weight fraction. Alloys with a higher concentration of Zn (Sn–9Zn, Sn–15Zn) formed corrosion products rich in Zn. The Zn-rich corrosion products were prone to spallation. The corrosion rate in the HCl solution decreased with decreasing weight fraction of Zn. The Sn–5Zn alloy had the lowest corrosion rate. The corrosion resistance in HCl could be considerably improved by reducing the proportion of zinc in Sn–Zn alloys.

In the present work, the corrosion behavior of the Mg2Sn alloy (Mg66.7Sn33.3, concentration in at.%) has been studied. The alloy was prepared from high purity Sn and Mg lumps by induction melting in argon. The alloy was composed of intermetallic Mg2Sn with a small amount of Mg2Sn + (Sn) eutectic. The corrosion behavior was studied by hydrogen evolution, immersion, and potentiodynamic experiments. Three aqueous solutions of NaCl (3.5 wt.%), NaOH (0.1 wt.%) and HCl (0.1 wt.%) were chosen as corrosion media. The alloy was found to be cathodic with respect to metallic Mg and anodic with respect to Sn. The corrosion potentials of the Mg2Sn alloy were −1380, −1498 and −1361 mV vs. sat. Ag/AgCl in HCl, NaCl and NaOH solutions, respectively. The highest corrosion rate of the alloy, 92 mmpy, was found in aqueous HCl. The high corrosion rate was accompanied by massive hydrogen evolution on the alloy’s surface. The corrosion rate was found to decrease sharply with increasing pH of the electrolyte. In the NaOH electrolyte, a passivation of the alloy was observed. The corrosion of the alloy involved a simultaneous oxidation of Mg and Sn. The main corrosion products on the alloy surface were MgSn(OH)6 and Mg(OH)2. The corrosion mechanism is discussed and implications for practical applications of the alloy are provided.

The microstructure, phase constitution, and corrosion performance of as-solidified Al70Pd25Co5 and Al74Pd12Co14 alloys (element concentrations in at.%) have been investigated in the present work. The alloys were prepared by arc-melting of Al, Pd, and Co lumps in argon. The Al74Pd12Co14 alloy was composed of structurally complex &epsilon, n phase, while the Al70Pd25Co5 alloy was composed of &epsilon, n and &delta, phases. The corrosion performance was studied by open circuit potential measurements and potentiodynamic polarization in aqueous NaCl solution (3.5 wt.%). Marked open circuit potential oscillations of the Al70Pd25Co5 alloy have been observed, indicating individual breakdown and re-passivation events on the sample surface. A preferential corrosion attack of &epsilon, n was found, while the binary &delta, phase (Al3Pd2) remained free of corrosion. A de-alloying of Al from &epsilon, n and formation of intermittent interpenetrating channel networks occurred in both alloys. The corrosion behavior of &epsilon, n is discussed in terms of its chemical composition and crystal structure. The corrosion activity of &epsilon, n could be further exploited in preparation of porous Pd&ndash, Co networks with possible catalytic activity.

In this work, the high temperature oxidation behavior of Al71Co29 and Al76Co24 alloys (concentration in at.%) is presented. The alloys were prepared by controlled arc-melting of Co and Al granules in high purity argon. The as-solidified alloys were found to consist of several different phases, including structurally complex m-Al13Co4 and Z-Al3Co phases. The high temperature oxidation behavior of the alloys was studied by simultaneous thermal analysis in flowing synthetic air at 773&ndash, 1173 K. A protective Al2O3 scale was formed on the sample surface. A parabolic rate law was observed. The rate constants of the alloys have been found between 1.63 &times, 10&minus, 14 and 8.83 &times, 12 g cm&minus, 4 s&minus, 1. The experimental activation energies of oxidation are 90 and 123 kJ mol&minus, 1 for the Al71Co29 and Al76Co24 alloys, respectively. The oxidation mechanism of the Al-Co alloys is discussed and implications towards practical applications of these alloys at high temperatures are provided.

Experiments play a decisive role in science and technical education on all levels. Active participation of students with special needs for skills improvement in higher technical education was rare until recently. One of the reasons was their inability to complete experimental measurements in university laboratories. Existing remote experiments on the Internet remove barriers facing disabled students and provide a novel option - to conduct laboratory tasks anytime and anywhere, even multiple times. The aim of this paper is to demonstrate the methodology of implementing e-experiments and virtual simulation dealing with the given topic by means of a prepared project assignment. As the topic of utilizing Internet accessible experiments has not yet been examined from the psychological point of view, we would like to address specialists and to initiate a discussion.

The paper describes the first experience with the set up, functioning and data evaluation of the remote experiment "Energy transformation" accessible via Internet (http://remotelab10.truni.sk ) as a part of the e-laboratory at the Department of Physics, Faculty of Education, Trnava University in Trnava, Slovakia. The remote experiment control and data acquisition is based on the system ISES (Internet School Experimental System) and its control program and www page are built using the environment Easy Remote ISES. The main goal of the experiment is the elucidation of the energy transformations of three types of well known energy sources - photovoltaic cell (solar energy to electrical energy), electrolyzer (electrical to chemical energy of hydrogen) and fuel cell (chemical energy of hydrogen to electrical energy) and finding optimal regimes for their maximum efficiencies. The perspective of the improvement of the experiment and its exploitation is given., Trnava University in Trnava [10/TU/13]; APVVSlovak Research and Development Agency [APVV 0096-11]; KEGA [011TTU-4/2012, 020TTU-4/2013]

Real remote laboratory experiment on Joule´s experimentation has both the historical and pedagogical importance in the building of the bridge between macro and micro world. Dissipative forces and their work as a transformation of the macroscopic mechanical energy into the energy of thermal movement are decisive in the study of mechanical phenomena of real world. The remote experiment should both qualitatively and quantitatively describe the transformation of macroscopic kinetic energy into heat and show the quantities, active in the transformation. The remote experiment represents a new generation of ISES remote experiments. The measureserver is equipped with a new diagnostics block, enabling diagnosis information on remote experiments both for the client and the provider.

This paper presents the results of a pedagogical research into the applicability of the new education strategy - Integrated e Learning (INTe-L) - and its implementation into project-based education. The research was conducted on the subject of Physics and the participants were in 9th grades of two Slovak primary schools. INTe-L is based on the utilisation of experiments (real, remote and virtual) and educational e-materials in the acquisition of the natural science knowledge, as well as the possibility of using scientific methods in the above-mentioned process. Pedagogical research into the topic "Energy and its transformation" showed, INTe-L is not only an appropriate motivational and interactive way of teaching Physics, but compared with traditional teaching, it also enables students to better understand real world features. (C) 2013 The Authors. Published by Elsevier Ltd.