Evangelia A. Pavlatou

S. Spanou, Α.Ι. Kontos, Α. Siokou, Α.G. Kontos, Ν. Vaenas, P. Falaras, E.A. Pavlatou

Electrochimica Acta (2013), 105, 324-332

Titanium dioxide (TiO₂) nano-particles were immobilized in nickel matrix coatings using the direct current electrodeposition technique. The influence of nickel surface morphology and crystallographic orientation on the photocatalytic activity and photo-induced hydrophilicity of the composite coatings were investigated under UVA illumination. The overall self-cleaning character of the composites was improved following the titania codeposition, as both hydrophilic and photocatalytic effects are present. Simultaneous optimization of the two functionalities was possible via tuning the titania percentage, indicating that the corresponding properties of the composite coatings are associated also to the induced crystalline nickel orientation and the nickel grain size. In particular, the data indicate that both enhanced photocatalytic activity and photo-induced hydrophilicity are achieved by increasing amounts of titania nano-particles embedded in the Ni matrix in combination with reduced grain size of nickel crystallites that are oriented towards the [110] axis.

doi: 10.1016/j.electacta.2013.04.174

M. Giallousi, V. Gialamas, E.A. Pavlatou

Learning Environments Research (2013), 16 (3), 349-366

The present study was the first in Greece in which educational effectiveness theory constituted a knowledge base for investigating the impact of chemistry classroom environment in 10 Grade students’ enjoyment of class. An interpretive heuristic schema was developed and utilised in order to incorporate two factors of teacher behaviour at classroom level, namely, ‘content coverage’ and ‘cognitive teaching processes’, with the patterns of a typology of classroom environments. The latter was drawn from data collected in Attica (a region in Greece) using a new and valid instrument, the How Chemistry Class is Working, while the Enjoyment of Chemistry Lessons scale was used to measure students’ attitudes. A two-step cluster analysis revealed four patterns of the typology that were adaptable to the heuristic schema. The relationship between the patterns and students’ gender, as well the variation in the level of students’ enjoyment among the patterns, were explored. The traditional chemistry classroom environments were found to prevail and to be less enjoyable for the students, especially for the girls. It was found also that students enjoy chemistry lessons more when their goals are taken into account and they have an active role in learning process.

doi: 10.1007/s10984-013-9133-y

A. Thanos, E. Katsou, S. Malamis, K. Psarras, E.A. Pavlatou, K.J. Haralambous

Chemical Engineering Journal (2012), 211-212, 77-88

The removal of Cr(VI) from aqueous solutions was investigated using various minerals, such as zeolite (clinoptilolite), bentonite, exfoliated vermiculite and attapulgite. These minerals were modified using hexadecylammonium bromide (HDTMA-Br). The parameters under investigation were the HDTMA-Br concentration (0.36–8 gL⁻¹), the pH (3–9) at which the modification process was conducted, the pH (3–9) of the adsorption solution, the modified mineral type and its concentration (1.5–10 gL⁻¹), the mineral–metal contact time, the chromium initial concentration (10–500 mgL⁻¹) and the system equilibrium time with respect to chromate adsorption. FTIR, SEM-EDX, XRD and electrokinetic zeta measurements were conducted for the natural and modified minerals which confirmed the modification of the minerals. The optimum pH for Cr(VI) adsorption was 4, in all the examined cases. The maximum adsorption capacity followed the order vermiculite (27 mgg⁻¹)>bentonite (24 mgg⁻¹)>attapulgite (15 mgg⁻¹)>zeolite (13 mgg⁻¹). Freundlich was the isotherm that provided the best fit to the experimental data when attapulgite was employed, while Langmuir was the most suitable one when the other three minerals were employed. Kinetics examination revealed a rapid adsorption of the metal during the initial stages. The pseudo-second-order equation fitted well to the experimental data.

doi: 10.1016/j.cej.2012.08.086

E.A. Pavlatou, P. Gyftou, S. Spanou

Transactions of the Institute of Metal Finishing (2012), 90 (5), 267-273

Nickel nanocrystalline electrodeposits were produced from a Watts type bath with the addition of cis-2-butene-1,4-diol and simultaneous application of either direct or pulse current conditions. The surface morphology, the preferred orientation, grain size and microhardness of Ni deposits were determined as functions of the concentration of the additive in bath, the type of imposed current and the frequency of imposed current pulses. The combined imposition of predefined pulse current conditions (pulse frequency) and specific additive concentration in the bath leads to specific textural modifications ([211] and [100] preferred crystal orientations) accompanied by considerable nanosized grain refinement of the coatings. The overall experimental data indicate that the production of hard and bright nanostructured deposits could be obtained under pulse current regime and reduced amounts of cis-2-butene-1,4-diol compared to direct plating.

doi: 10.1179/0020296712Z.00000000049

G. Korakakis, A. Boudouvis, J. Palyvos, E.A Pavlatou

Procedia - Social and Behavioral Sciences (2012), 31, 145-149

This study reports research findings on whether the use of 3D visualization types i.e. Interactive 3D Virtual Environment (I3DVE), 3D Animations Interface (3DAIF) and 3D Static Illustrations Interface (3DSIIF), combined with narration and text in multimedia applications, contributes to the learning process of 12th grade students in science. A total of 111 students participated in the research that utilized three different versions of an interactive multimedia application called "Atomic Orbitals". The research results provide convincing evidence that I3DVE have a greater contribution to the learning process than the other two types of visualization.

doi: 10.1016/j.sbspro.2011.12.032

K. Dalacosta, M. Paparrigopoulou-Kamariotaki, E.A. Pavlatou

Procedia - Social and Behavioral Sciences (2011), 15, 3272-3276

The present paper concerns the use of animated cartoons as an assessment tool in teaching science regarding students of elementary education. Different instructional strategies are presented whereas with the aid of two sets of questions with animated cartoons, the teacher is able to: (i) find out and evaluate what students already know about specific science concepts or (ii) evaluate students’ knowledge and understanding of science concepts which are normally difficult to comprehend and often cause misconceptions to them. Concepts that have been chosen to be studied were those of mass volume and density, as well as dissolving, melting, and disappearing.

doi: 10.1016/j.sbspro.2011.04.284

S. Spanou, E.A. Pavlatou

Zeitschrift fur Physikalische Chemie (2011), 225 (3), 313-324

Nanocomposite coatings were obtained by electrochemical codeposition of TiO₂ nano-particles (mean diameter 21nm, Degussa P25) with nickel, from an additive-free Watts type bath. Pure Ni and composite Ni-TiO₂ coatings were electrolytically deposited under both direct and pulse current conditions and an extended region of electrolysis conditions (pH, current density, TiO₂ loading in the bath). Pure Ni deposits were produced under the same experimental conditions for comparison. The aim of this study was to correlate the observed structural characteristics of the coatings (crystallographic orientation and grain size of nickel matrix,) and incorporation percentage with the resulting microhardness values and tribological behavior. Overall, the data have demonstrated that when attributing the observed strengthening effect of composites, not only grain refinement and dispersion strengthening mechanisms, but also preferred crystalline orientation should be taken into consideration. The variation of the wear rate is directly associated with the microhardness variations and consequently, governed by the same parameters that determine the synergistic strengthening mechanism proposed. Pure and composite coatings with [110] crystalline orientation exhibited the highest microhardness values and wear resistance.

doi: 10.1524/zpch.2011.0052

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

Journal of Alloys and Compounds (2010), 494, 396-403

Ni–P/SiC composite coatings were produced under both direct and extended pulse current conditions from an additive-free modified Watts type bath at various hydrodynamic conditions. Structural analysis revealed an amorphous phase of Ni–P matrix for the majority of coatings, except for those prepared under low duty cycle and high frequency pulses that exhibited mainly the crystalline Ni₁₂P₅ compound. The practice of pulse plating regime led to composite coatings with higher incorporation rate of SiC particles (up to 22wt.) and microhardness values (up to 7.2GPa) than those produced under direct current conditions. It has been revealed that increased micron-SiC codeposition percentage resulted in decrease of P content in the amorphous matrix and increase of the deposits’ hardness values. After annealing at 400°C the amorphous matrix was crystallized to phases of Ni, Ni₂P, and Ni₃P, the formation of which depends on the P content. As-plated deposits exhibiting Ni₁₂P₅ phase preserved this crystalline structure after thermal treatment. Annealed coatings exhibited almost double values of microhardness relative to those of the as-deposited coatings.

doi: 10.1016/j.jallcom.2010.01.057

S. Spanou, E.A. Pavlatou

Journal of Applied Electrochemistry (2010), 40, 1325-1336

Pure and composite nickel deposits containing nano-TiO₂ particles (dm=21nm) were produced under direct-DC and pulse current-PC conditions. The influence of pulse frequency on the codeposition of TiO₂ particles, preferred orientation of Ni crystallites and grain size, as well as microhardness of the composites, was investigated systematically. Composites prepared in PC regime displayed higher incorporation percentage than those obtained under DC conditions, and the highest incorporation rates were achieved at pulse frequencies ν>100Hz. The application of pulse frequency accompanied by the embedding of TiO₂ nanoparticles in the nickel matrix resulted in a strong influence upon the crystalline orientation, the grain size and the corresponding microhardness. All composites exhibited higher microhardness values compared to the pure deposits, independent of the applied current conditions. Overall, when ascribing the observed strengthening effect of composites, not only grain refinement and dispersion strengthening mechanisms but also preferred crystalline orientation should be taken into consideration.

doi: 10.1007/s10800-010-0080-3

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

N. Spyrellis, A. Zoikis-Karathanasis, P. Gyftou, E.A. Pavlatou

Galvanotecnica e nueve finiture AIFM (2009), XIX-LX, 268-286 (in Italian)

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 HNO_3(aq), HCl_(aq) and H₂SO_4(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

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 8^th 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 (C_BD=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