Papers

M. Giallousi, V. Gialamas, N. Spyrellis, E.Α. Pavlatou

International Journal of Science and Mathematics Education (2010), 8, 761-782

This study describes the development and validation of a Greek-language instrument that can be used to assess grade 10 students' perceptions of their chemistry classroom environment as a means of showing differences between chemistry learning environments in Greece (Attica) and Cyprus. The development of the instrument was based on available learning environment questionnaires. The questionnaire was administered to 1.394 students from 49 chemistry classes in Attica, and the resulting data were analyzed to explore the reliability and the validity of the new instrument. The validated questionnaire was administered to 225 students from 15 classes in urban areas of Cyprus. The data analyses supported the questionnaire's internal consistency, discriminant validity, and ability to differentiate between classrooms. Effect sizes and independent samples t test analyses revealed differences between the two samples. Cypriot students viewed their chemistry classroom environment more favorably than did the Attica students. A possible cause for this difference could be the knowledge-centered aspect of the grade 10 chemistry curriculum in Greece compared to the corresponding tool-instrumental knowledge curriculum in Cyprus.

doi: 10.1007/s10763-009-9184-9

X. Vamvakeros, E.A. Pavlatou and N. Spyrellis

Science and Education (2010), 19, 119-145

A survey exploring the views of scientists, chemists and chemical engineers, on current trends in Chemistry Education was conducted in Greece. Their opinions were investigated using a questionnaire focusing on curricula (the content and process of chemistry teaching and learning), as well as on the respondents’ general educational beliefs and their underlying epistemological views. The aim of this work was to investigate the respondents’ opinions and, if possible, to identify the areas where convergence or even consensus occurred. The results showed that some of the items on the research questionnaire produced a high degree of agreement with the respondents’ views, while a few others were exactly the opposite. These items are considered to be representative of more widespread views. In order to explore the diverging opinions, the items on the research questionnaire that showed great variance were analyzed to determine, whether or not there were significant inter-item correlations among subgroups of participants with different demographic characteristics. Postgraduate studies, professional occupation, age/experience, and career within or outside the wide educational sector were among the main factors that significantly influenced the research results. The study did not reveal any single belief framework underlying the opinions of the respondents. Nevertheless, three specific approach frameworks—ACADEMIC, CONSTRUCTIVIST and SCIENTIFIC REALISM—were analyzed to determine which had the highest degree of agreement. It was found that the SCIENTIFIC REALISM framework and the curriculum emphasis characteristic of the context-based CTSE (Chemistry, Technology, Society and Environment) prevailed, as they produced a significantly higher mean score. The ACADEMIC framework followed with a moderate mean score and the CONSTRUCTIVIST framework had a lower mean score.

doi: 10.1007/s11191-009-9196-4

I. Masavetas, A. Moutsatsou, E. Nikolaou, S.Spanou, A. Zoikis-Karathanasis, E.A. Pavlatou, N. Spyrellis

Global NEST Journal (2009), 11 (2), 241-247

During the last years, the waste electrical and electronic equipment (WEEE) are gathering attention, as a very special section of waste. In fact, they have been proven to be source for the recovery of metals. In the present study printed circuit boards (PCBs) were cut and treated thermally at 500°C for 1h in both air and nitrogen atmosphere. The obtained material was dissolved in three different acid media HNO3(aq), HCl(aq) and H2SO4(aq), in order to extract copper. The achieved Cu recovery percentages were 97.5, 65 and 76.5% respectively. Electrodeposition technique was applied in order to recover copper in powder form. More than 98% of copper was recovered achieved by application of high current density resulting to dendritic structure of copper. The applied process was characterised by a high current efficiency and led to the production of copper powder of 80μm mean diameter appropriate for powder metallurgy applications.

doi: 10.30955/gnj.000595

N. Spyrellis, E.A. Pavlatou, S. Spanou, A. Zoikis-Karathanasis

Transactions of Nonferrous Metals Society of China (2009), 19 (4) 800-804

Nickel and nickel-phosphorous matrix composite coatings reinforced by TiO2, SiC and WC particles were produced under direct and pulse current conditions from an additive-free Watts' type bath. The influence of the variable electrolysis parameters (type of current, frequency of current pulses and current density) and the reinforcing particles properties (type, size and concentration in the bath) on the surface morphology and the structure of the deposits was examined. It is demonstrated that the embedding of ceramic particles modifies in various ways the nickel electrocrystallisation process. On the other hand, Ni-P amorphous matrix is not affected by the occlusion of the particles. Overall, the imposition of pulse current conditions leads to composite coatings with increased embedded percentage and more homogenous distribution of particles in the matrix than coatings produced under direct current regime.

doi: 10.1016/S1003-6326(08)60353-2

G. Korakakis, E.A. Pavlatou, J.A. Palyvos, N. Spyrellis

Computers & Education (2009), 52, 390-401

This research aims to determine whether the use of specific types of visualization (3D illustration, 3D animation, and interactive 3D animation) combined with narration and text, contributes to the learning process of 13- and 14-years-old students in science courses. The study was carried out with 212 8th grade students in Greece. This exploratory study utilizes three different versions of an interactive multimedia application called “Methods of separation of mixtures”, each one differing from the other two in a type of visuals. The results indicate that multimedia applications with interactive 3D animations as well as with 3D animations do in fact increase the interest of students and make the material more appealing to them. The findings also suggest that the most obvious and essential benefit of static visuals (3D illustrations) is that they leave the time control of learning to the students and decrease the cognitive load.

doi: 10.1016/j.compedu.2008.09.011

S. Spanou, E.A. Pavlatou, N. Spyrellis

Electrochimica Acta (2009), 54, 2547-2555

Nanocomposite coatings were obtained by electrochemical codeposition of TiO2 nano-particles (mean diameter 21nm) with nickel, from an additive-free Watts type bath. The electrodeposition of Ni–TiO2 composites was carried out on a rotating disk electrode (RDE), by applying direct current. Pure Ni deposits were also produced under the same experimental conditions for comparison. The surface morphology, the crystallographic orientation of nickel matrix and the grain size of the deposits were investigated, along with the distribution and the percentage, of the embedded nano-particles in nickel matrix, as a function of pH, current density and concentration of TiO2 nano-particles in the bath. The observed textural modifications of composite coatings are associated with specific structural modifications of Ni crystallites provoked by the adsorption–desorption phenomena occurring on the metal surface, induced by the presence of TiO2 nano-particles. It has been observed that the presence of TiO2 nano-particles favours the [100] texture of nickel matrix. Moreover, the codeposition of titania nano-particles with nickel was found to be favoured at low pH and low applied current values. As the titania incorporation percentage is increased, a considerable grain refinement in the nanometer region was revealed followed by an improvement of the quality of the nickel preferred orientation.

doi: 10.1016/j.electacta.2008.06.068

A. Zoikis Karathanasis, E.A. Pavlatou, N. Spyrellis

Electrochimica Acta (2009), 54, 2563-2570

In the present work pure nickel–phosphorous and nickel–phosphorous composite coatings with WC particles (mean diameter 200nm) have been produced under both direct and pulse current conditions, from a modified, organic-free, Watts bath. The produced coatings were thermally treated at various temperatures and the structure, morphology and the microhardness of the deposits were examined after each cycle of heat treatment. Imposition of pulse current conditions led to composite deposits with high-incorporation percentage of WC particles in the matrix. Also, the presence of WC particles resulted in coatings with enhanced microhardness values and retarded diffusion phenomena in the deposits during thermal treatment. Annealing of all coatings at 400°C revealed complete crystallization of the matrix to the phases of Ni, Ni2P and Ni3P accompanied by a significant increase of microhardness for all deposits. Further heating at higher temperatures demonstrated a decrease in microhardness of both kinds of deposits. The experimental data proved that it is possible to produce NiP–WC composite coatings under specific pulse current conditions followed by proper thermal treatment that exhibited considerable enhanced microhardness.

doi: 10.1016/j.electacta.2008.07.027

P. Gyftou, E.A. Pavlatou, N. Spyrellis

Applied Surface Science (2008), 254, 5910-5916

Pure nickel and nickel matrix composite deposits containing nano-SiC particles were produced under both direct and pulse current conditions from an additive-free nickel Watts’ type bath. It has been proved that composite electrodeposits prepared under pulse plating conditions exhibited higher incorporation percentages than those obtained under direct plating conditions, especially at low duty cycles. The study of the textural perfection of the deposits revealed that the presence of nano-particles led to the worsening of the quality of the observed [100] preferred orientation. Composites with high concentration of embedded particles exhibited a mixed crystal orientation through [100] and [211] axes. The embedding SiC nano-particles in the metallic matrix by an intra-crystalline mechanism resulted in the production of composite deposits with smaller crystallite sizes and more structural defects than those of pure Ni deposits. A dispersion-hardening effect was revealed for composite coatings independently from applied current conditions. Pulse electrodeposition significantly improved the hardness of the Ni/SiC composite deposits, mainly at low duty cycle and frequency of imposed current pulses.

doi: 10.1016/j.apsusc.2008.03.151

E.A. Pavlatou, N. Spyrellis

Russian Journal of Electrochemistry (2008), 44, 745-754

An additive-free Watts type bath containing micron- and nano-SiC particles (1μm and 20nm respectively), as well as ultrafine-WC particles (200nm), was used for the production of pure Ni and nickel matrix composite electrocoatings under both direct and pulse current conditions. Moreover, nickel nanocrystalline deposits were obtained from a Watts type bath containing small amounts of 2-butyne-1,4-diol, in order to investigate the combined advantages of additives and pulse technique on the properties of the deposits. The influence of the variable electrolysis parameters, the particle size and the organic additive concentration on the surface morphology, the structure and properties of the deposits were discussed. It has been proved that the application of pulse electrodeposition affects drastically the structural characteristics and properties of the deposits and under well-defined conditions could lead to the preparation of nanostructured materials with improved mechanical properties.

doi: 10.1134/S1023193508060165

E.A. Pavlatou, M. Raptakis, N. Spyrellis

Surface & Coatings Technology (2007), 201, 4571-4577

Nanocrystalline nickel deposits were produced by applying both direct current (DC) and pulse current electroplating (PC) from an additive-free Watts type bath and in the presence of 2-butyne-1,4-diol (BD). The surface morphology, the preferred orientation, the grain size and the microhardness of the deposits were investigated. Under DC conditions, the addition of BD enhanced the perfection of [100] preferred crystal orientation and promoted a considerable grain refinement. The application of PC technique in presence of small amount of BD (CBD=0.25 mmolL−1) accelerated the textural modification from [100] to [211] with respect to DC conditions and deposits with grain size of 20–60nm were produced. A significant enhancement of microhardness of the produced bright deposits was observed compared to those deposits prepared under DC regime, which could be correlated to the observed crystal orientation mode [211], as well as to the corresponding nanosized crystallites. Progressive addition of BD promoted a peculiar textural modification from [211] to [100] and a possible mechanism of action of BD is proposed taking into account as inhibiting species of the Ni crystal growth not only Ni(OH)2, but also cis-butene-1,4 diol.

doi: 10.1016/j.surfcoat.2006.09.113

E.A. Pavlatou, M. Stroumbouli, P. Gyftou, N. Spyrellis

Journal of Applied Electrochemistry (2006), 36, 385-394

Pure Ni and nickel matrix composite electrocoatings containing micron- and nano-SiC particles (1μm and 20nm respectively) were produced under direct and pulse current conditions from an additive-free Watts type bath. The effect of the particle size, codeposition percentage of SiC and type of imposed current on the microhardness as well as on the microstructure of the electrodeposits were investigated. Ni/SiC composite deposits prepared under either direct or pulse current conditions exhibited a considerable strengthening effect with respect to pure Ni coatings. The improved hardness of composite coatings was associated to specific structural modifications of Ni crystallites provoked by the adsorption of H+ on the surface of SiC particles, thus leading to a (211) texture mode of Ni crystal growth. Pulse electrodeposition significantly improved the hardness of the Ni/SiC composite coatings, especially at low duty cycles, in which grain refinement and higher SiC incorporation (vol.%) was achieved. The enhanced hardness of Ni/nano-SiC deposits, as compared to Ni/micron-SiC composites, was attributed to the increasing values of the number density of embedded SiC particles in the nickel matrix with decreasing particle size. In addition, the observed hardening effects of the SiC particles might be associated to the different embedding mechanisms of the particles, which could be characterized as inter-crystalline for micron-SiC and partially intra-crystalline for nano-SiC particles.

doi: 10.1007/s10800-005-9082-y

P. Gyftou, M. Stroumbouli, E.A. Pavlatou, P. Asimidis, N. Spyrellis

Electrochimica Acta (2005), 50, 4544-4550

Nickel matrix composite coatings containing micro and nano-sized SiC particles were prepared from an additive-free Watts’ type solution under direct and pulse current conditions, in order to study the correlation between SiC particles embedding and the tribological behaviour of deposits. The wear properties of Ni/SiC composite coatings were shown to depend on the type of current, the size of the embedded particles, the weight fraction of codeposited particles, the microstructural modifications induced by codepositing SiC particles and the plating conditions. It was proved that the presence of SiC particles influences the adsorption–desorption phenomena occurring at the metal-catholyte interface during electrocrystallization and, synergically with the plating conditions, modifies the deposits microstructure thus affecting wear properties.

doi: 10.1016/j.electacta.2004.10.090

M. Stroumbouli, P. Gyftou, E.A. Pavlatou, N. Spyrellis

Surface and Coatings Technology (2005), 195 (2-3), 325-332

The electrolytic codeposition of ultrafine WC particles (mean diameter of 0.2μm) from an additive-free nickel Watts' solution by applying both direct (DC) and pulse (PC) electroplating, has been investigated. Electrodeposition of Ni/WC composites was carried out on a rotating disk electrode (RDE) at various rotation velocities. The effect of type current and hydrodynamic conditions of the plating bath on the codeposition of WC particles with Ni matrix has been reported. The crystallographic orientation of nickel matrix, the distribution and the percentage of the embedded particles, were examined as well as the structure and the surface morphology of the produced composite coatings. It was found that electrodeposits prepared at DC conditions and low rotation velocities are highly porous. On the contrary, when applying PC conditions and high rotation velocities, compact deposits with high concentration of embedded WC particles and uniform distribution were produced. It has been observed that the presence of WC particles in the metal matrix imposes an almost random orientation of Ni crystallites along with a reinforcement of [210] orientation. Taking into consideration a surface complexation model and the experimental data, a mechanism of nickel electrocrystallization in the presence of WC particles has been proposed.

doi: 10.1016/j.surfcoat.2004.06.034

S. Boghosian, E.A. Pavlatou, G.N. Papatheodorou

Vibrational Spectroscopy (2005), 37, 133-139

The vapors of NbF5 and TaF5 have been investigated by Raman spectroscopy in the temperature range 475–675K and at total pressures from ∼0.1 to ∼4.0atm. The temperature and pressure dependence of the spectra is indicative of equilibrium shifts between monomer and associated (polymer) gaseous species. The intensities of Raman bands, which were characteristic of the various species present, were exploited in order to establish the stoichiometry and thermodynamic functions of the reaction nMF5(g) ⇆ MnF5n(g) (M=Nb, Ta). It was found that unambiguously n=2 in the studied temperature range, which implied that the predominant vapor species are monomers MF5(g) and dimers M2F10(g). The thermodynamic functions according to the studied dimerization reactions were measured from the Raman data as: (a) ΔHR=−104.3±2.4 kJmol−1, ΔSR=−175±20 Jmol−1K−1 for 2NbF5(g) ⇆ Nb2F10(g); (b) ΔHR = −101.1±3.7 kJmol−1, ΔSR=−150±30 Jmol−1K−1 for 2TaF5(g) ⇆ Ta2F10(g).

doi: 10.1016/j.vibspec.2004.08.004

S.A. Kirillov, E.A. Pavlatou, G.N. Papatheodorou

The Journal of Chemical Physics (2002), 116 (21), 9341-9351

The picosecond dynamics of molten alkali halides is discussed, and the low-frequency Raman spectra of molten LiCl, CsCl, and the LiCl–CsCl eutectic are fitted to the model enabling to obtain the times of vibrational dephasing, τV and vibrational frequency modulation τω. In terms of the Wilmshurst criterion [J. Chem. Phys. 39, 1779 (1963)] and using the data of NMR studies and molecular dynamics simulations, a conclusion is drawn that molten alkali halides cannot contain long-lived stable complexes with lifetimes greater than 10−8 s. The low-frequency Raman spectra of molten alkali halides and their mixtures probe the presence of instantaneous spatial configurations of MXn−n+1 type, where M+ is the alkali metal cation and X is the halide anion existing in melts during the time intervals equal to the time of duration of collision of oppositely charged ions τd, which is less than 0.5ps. This time is sufficient to a collision complex to execute several (at least one) vibrations. Vibrational dephasing and modulation processes elapse during this same time, thereby indicating the instantaneous nature of configurations in question. To discern between short-lived and long-lived complexes, we propose relations between the minimal damping time of the probe oscillator set equal to the half-period of vibration T/2, τV, τω, and τd, as well as the time between collisions τBC. The duration of an act resulting in the vibrational phase shift (or energy transfer) must be equal to (or longer than) the half-period of vibration of the probe oscillator, τV≥T/2. The modulation time may vary from this same half-period of vibration or the time between collisions τBC to very long times, τω≥T/2, τω≥τBC. For short-lived complexes, the longest of two characteristic times describing the phase decay cannot exceed possible duration of collision, τω⩽τd, τV⩽τd. Cs-containing configurations follow this definition and therefore should be considered instantaneous short-lived collision complexes: their τV≈T/2∼0.1ps, and τω≈τBC∼0.03ps. Li-containing configurations appear to be relatively long-lived: their lifetimes could be associated with τω∼0.17ps, which is several times longer than any other shortest possible characteristic time in the system (τBC∼0.026ps or T/2∼0.05ps). In light of these conclusions, an a priori assumption of autocomplex MX4n−4 anions and Mn+ cations as being structural elements of molten halides made in the so-called autocomplex model by Smirnov, Shabanov, and Khaimenov [Elektrohim. 2, 1240 (1966)] is discussed, and the autocomplexes are identified as instantaneous short-lived configurations detectable by the Raman method.

doi: 10.1063/1.1473810

P. Gyftou, M. Stroumbouli, E.A. Pavlatou, N. Spyrellis

Transactions of the Institute of Metal Finishing (2002), 80 (3), 88-91

Nickel matrix composite coatings containing micron- and nano-sized SiC particles were prepared in order to study the interdependence of the SiC particles embedding and the deposits 'mechanical behaviour. SiC particles of two different sizes, namely 1μm and 20nm, were codeposited with nickel from Watts solutions under pulse current conditions. It has been observed that the embedding of SiC particles in the nickel matrix and the pulse current application result in deposits with more uniform particle distribution and better surface morphology than those obtained under direct current conditions. The study of the composite deposits revealed that the microhardness is not only increased by the presence and the reduced size of the particles, but also influenced by the current conditions, i.e. duty cycle and pulse frequency. Moreover, microhardness of the deposits can be further ameliorated by specific thermal treatment.

doi: 10.1080/00202967.2002.11871440

S.A. Kirillov, G.A. Voyiatzis, I.S. Musiyenko, G. M. Photiadis, E.A. Pavlatou

The Journal of Chemical Physics (2001), 114 (8), 3683-3691

In this article we present the first quantitative estimates of the spectroscopically active part of the interaction potential in molten complex chlorides based on dephasing studies. We have selected the molten salt systems containing quasispherical complex MCl4−2 anions (M=Mn+2 and Zn+2) and performed the study of their ν1(A1isotropic Raman line profiles as a function of the temperature and concentration. We have analyzed the form of the time correlation function of vibrational dephasing and determined the type of modulation events, which cause the line broadening processes in these systems; these are found to be purely discrete Markovian. Within the formalism of the purely discrete Markovian modulation, we have made a judgement about spectroscopically active interactions in these systems. Interionic potential in complex chlorides is dominated by the attraction forces, which depend on the interparticle distance r as r−4, and by repulsion of the r−7-type.

doi: 10.1063/1.1340031

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