C. T. Dervos et al.: Effect of Water on Permittivity of Nanodielectrics Exposed to the Atmosphere

1070-9878/09/$25.00 © 2009 IEEE

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Effect of Water on Permittivity of Nanodielectrics Exposed to the Atmosphere

C. T. Dervos, J. A. Mergos, P. D. Skafidas, M. D. Athanassopoulou and P. Vassiliou

National Technical University of Athens School of Electrical and Computer Engineering

Zografou Campus, 15780 Greece

ABSTRACT Relative dielectric constant and dissipation factor (tanδ) values as a function of frequency have been measured for a variety of water types. The effect of water absorption on the permittivity properties of crystalline powders or nanopowders when exposed to various humidity levels is also examined. Powdered materials were characterized by XRD and were consisting of calcite (CaCO3), anatase, rutile (TiO2), γ- and δ-alumina (Al2O3). The induced polarization changes in the materials by the applied dehydration process, i.e. either high vacuum of 10-4 Pa (10-6 mbar) drying, or calcination in air at temperatures of up to 600 °C, were investigated. The advantage offered by vacuum dehydration is that nano-dielectrics maintain their particle size and crystal integrity. Index Terms - Permittivity measurement, dielectric polarization, water, surface, interface, nano-dielectric.

1 INTRODUCTION

THE aim of the present work is to identify the induced

electronic changes in nano-crystals by moisture absorption. It targets to demonstrate experimentally that as the particle size is reduced from “micro” to “nano” and the surface-to-volume ratio increases, the high surface-state electronic density governs the overall electrical response of the particles [1, 2]. The nanoparticles due to high surface reactivity readily react with gaseous molecules or moisture to minimize their surface energy. The electronic properties of powdered crystals are modified by the absorption of water molecules that induce molecular polarization over the surface. This acts in synergy with any preexisting polarization mechanism in the nano-crystals, i.e. interfacial, molecular, ionic, space charge, electronic [3-5]. Polymeric composite materials, or emulsions, may contain nano-dielectric fillers that dominate the overall insulating properties of the matrix [6]. During the fabrication process of composite materials the nano-fillers must be free of any attached water molecules to exclude either free water in nano-voids or bound water molecules to the polymer chain, and minimize molecular polarization of the composite in the frequency range of industrial applications [6, 7].

In this work the dielectric properties of various water samples were investigated and related to induced complex permittivity changes of nano-powders exposed to the atmosphere under various humidity levels. The work aims to investigate experimentally whether surface-attached water molecules significantly modify the overall electrical response

of nano-dielectrics exposed to water vapor, in which case their volumes become electrostatically screened.

2 EXPERIMENTAL

2.1 LIQUID SAMPLE SELECTION

Various types of water samples were selected in order to

investigate their dielectric characteristics as a function of frequency. The examined liquids were: (i) bidistilled water, which was measured within one hour after production, (ii) de-ionized water, which was also used to establish the various environmental humidity conditions, (iii) mineral water and (iv) various salinity water solutions, i.e. NaCl 0.1%, 0.5%, 1.0% and 2.0%, to demonstrate moisture intake in a coast environment.

The test electrodes used for dielectrometry measurements of powders could be inserted in an environmental chamber in order to identify any humidity-induced changes on complex permittivity of microcrystalline and nano-crystalline powdered compacts. In this work, the de-ionized water samples were used to obtain the required relative humidity levels in the chamber under constant temperature (25 °C).

2.2 SOLID MATERIAL SELECTION

A variety of micro-crystalline and nano-crystalline high-

purity powders either fabricated for the purpose of the study, or commercially available, were employed. Crystal structures were characterized by x-ray diffraction (XRD) and particle sizes were determined either by granulometry measurements or by scanning electron microscopy (SEM). Manuscript received on 3 October 2008, in final form 4 May 2009.

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2.2.1 CALCITE (CaCO3) SAMPLES

The calcite powders were prepared from fine quality well-crystallized white Pentelic marble consisting of solid blocks (30 mm x 50 mm x 200 mm) [8]. This material has been well studied by workers in the field, and it is known, since it was used as construction material for building a great number of precious ancient artifacts in Greece, including the Parthenon in the Acropolis of Athens. To record the electrical parameters of the solid material, planar slices were cut out by water-cooled diamond saw. These reference samples were 3 mm x 30 mm x 50 mm and their surfaces were mechanically polished to 600 grid and cleaned by de-ionized water. Granular particles having maximum diameter of 3 mm were produced from the raw solid material by pulverizing and successive sieving. The powder compact was produced by subsequent milling of the granular particles in an agate ball mill for approximately 1 h. The so produced coarse powder will be referred as “powder A”. Additional 20 minute mechanical milling of the coarse powder A by means of an agate mortar and pestle, produced powders with finer particles, that will be referred as “powder B”. The produced specimens, (solid, powder A, powder B) were characterized after their preparation process in terms of their crystalline integrity by X-Ray Diffraction Spectrometry (Siemens 5000), to confirm that the produced fine particles had maintained their calcite structure. It was experimentally confirmed that all calcite characteristic peaks remained unaltered, denoting the absence of crystal induced changes in preferential orientation and/or contamination during the powdering process. This is clearly shown by the XRD results given in Figure 1. The grain size distribution for powders A and B was measured by a Malvern laser granulometer, type Mastersizer/E. Aqueous solutions of the examined powders were subjected to ultrasound vibrations to disrupt agglomera-tions. According to the granulometry results shown in Figure 2, for the coarse powder A the highest concentration was found for particle diameters between 15-18 μm (6.1%), while 2.1% of the particles had diameters below the 590 nm. For the fine powder B, the highest particle concentration was practically met between 10-12 μm (4.1%), while 7.1% of the particles had diameters below the 590 nm.

2.2.2 TiO2 SAMPLES

Two different commercially available crystalline TiO2 powders were employed: (a) Merck product no. 1.00808, of 99.0% purity anatase TiO2 with grain size range 200-500 nm. The typical inclusions were 0.5% H2O, 0.05% SO4

-2, 0.005% Pb, 0.005% Fe, and (b) Sigma-Aldrich product No. 637262, of 99.9% (metal basis) TiO2 rutile nano-powder, with typical grain size (diameter x length) 10 nm x 40 nm, and specific surface 130-190 m2/g.

Mixtures of these TiO2 powders were obtained for weight ratios 50%-50%. The dry mixing process was preferred since it provides comparable results with the wet dopant solution

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techniques [9] and does not expose the nano-particle surfaces to solvents or water.

2.2.3 Al2O3 SAMPLES

Two different commercially available Al2O3 powders were employed: (a) Merck code no.1.01077, δ- alumina with grain size distribution 63-300 μm, and maximum water content 1.2% by the manufacturer. (b) Sigma-Aldrich code No. 544833 γ-alumina nanopowder, with grain size 50 nm and specific surface 35-43 m2/g. The latter is a very hygroscopic material.

Mixtures between the aforesaid Al2O3 powders were obtained by the dry mixing process for various weight ratios by mixing mechanically 3 g of the constituents in an agate mortar and pestle.

2.2.4 SAMPLE COMPRESSION TO FORM POWDER COMPACTS

The selected powder samples, or powder mixtures, were pressed uniaxially in a mould by a hydraulic press at pressures varying between 1.4 x 106 and 2.1 x 106 Pa (200 and 300 psi) for a period of 20 min, to form cylindrical pellets of 16 mm diameter and 3 mm thick. The application of mechanical pressure causes the smaller particles to work their way into the existing spaces between the larger particles, thus reducing the intermediate void concentration of the pellets (highly pressed powders). The obtained pellets maintained their form and mechanical integrity.

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2.3 CHARACTERIZATION BY DIELECTRIC SPECTROSCOPY

The dielectric properties of selected samples (either

liquids or solid samples exposed to different humidity levels) were investigated by the frequency dependence of complex permittivity (real and imaginary part). Measurements were performed by the capacitance method [10, 11] in a frequency range varying between 20 Hz - 1 MHz. To accomplish this measuring task a multi-frequency high precision LCR meter (Agilent-4284A equipped with option 001) was used in the parallel equivalent C-G mode.

For the case of liquid samples, the liquids under test had to fill the parallel plate capacitor of the Agilent-16452A liquid test fixture. The gap between the parallel plates was 3 mm and the test fixture was connected to the LCR unit by a four terminal configuration (Lc Lp Hc Hp) using the 16048A test leads. For this measuring electrode assembly the dielectric constant accuracy at 1 MHz is ±0.3 % [12].

For the case of cylindrical pellets, the samples under test were positioned among the parallel plate capacitor of Agilent-16451B dielectric test fixture. These test electrodes allow for dielectric characterization on small surfaces offering dielectric constant measuring accuracy ±1 % at 1 MHz and dissipation factor (tanδ) measuring accuracy ±5%, at 1 MHz). The measuring electrodes were inserted in an environmental chamber offering relative humidity level control under constant temperature, in order to explore the humidity-induced changes in the electrical response of the examined powdered compacts.

3 RESULTS AND DISCUSSION

3.1 LIQUID SAMPLES According to the results of Figure 3a, at greater

frequencies than 100 kHz the relative permittivity of water is 83 for all tested water purity conditions and examined solutions. At lower frequencies the relative permittivity increases due to polarization processes. The polarization onset may be shifted towards lower frequencies depending on water purity condition or type of incorporated impurity. At a characteristic relaxation frequency the tanδ value increases towards a maximum that is of the order of 85, as shown in Figure 3b. The bidistilled water sample, which is of the highest purity, develops the tanδ peak at 100 Hz immediately after production, but the peak shifts towards higher frequencies with elapsing time (i.e. few hours following) possibly due to gaseous contamination. Therefore, permittivity data (tanδ vs. frequency) could be utilized to follow state of cleanliness of ultra pure water samples.

The large dielectric constant of water ≅78 at 1 MHz at room temperature, contributes to make it the most important polar solvent in chemistry and biology. Crystalline water structures with an intact H-bond network, such as ice, exhibit even larger

Types of water

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(b) Figure 3. (a) Relative dielectric constant κ′, and (b) dissipation factor tanδ, values as a function of test frequency for the various examined water types.

dielectric constants (≅96.5 at 1 MHz at freezing temperature). Yet, a detailed understanding of the significance of the dielectric properties of water, based on first-principles microscopic theory, is still missing. Water molecular polarization rises by the fact that oxygen has a higher electronegativity than hydrogen. As a result, the side of the molecule with the oxygen atom has a partial negative charge, while the side with the hydrogen atoms has a partial positive charge. Any molecule with such a charge distribution will form a dipole, having the moment and dimensions shown in Figure 4a. However, the dielectric constant of water is higher than that of all other polar liquids made of molecules with similar dipole moments. This is attributed to the presence of an underlying hydrogen bonding scheme (H-bond) network, that is formed as the water molecules stick between themselves by cohesion forces due to their polar nature [13]. The additional polarizability induced in water by the hydrogen bonds is schematically depicted in Figure 4b. Here, the net polarization can be attributed (i) to the molecular polarization of water molecules and (ii) the polarization formed between neighboring molecules interconnected by the hydrogen bonds.

In the atmosphere, water vapors may contain some popula-tions of water oligomers (H2O)i (g). Across the oligomer chains all water molecules are attached by hydrogen-bonds and all inter-oxygen distances are equal, as shown in Figure 5.

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Depending on the scheme formed by the bonded molecules across the oligomer chain, these can be characterized as: Bifurcated hydrogen bonded Chains (BCs), Transverse Hydrogen Bonded Chains (t-HBCs), and Longitudinal Hydrogen Bonded Chains (l-HBCs) [14]. The net polarization across an oligomer chain is strong because the discrete dipoles developing by the hydrogen bonds are almost co-directional (Figure 5). Thus, the amplitude of the resulting vector-sum is augmented because the discrete dipoles are not canceling out each other.

Different bonding schemes among water molecules will result to different polarization degrees of the liquid [15]. This phenomenon becomes more intense at lower frequencies where the molecules have more time to orientate their polarization vectors of different origin with the externally applied field. Any additional polarization source in the liquid i.e. ionic due to the presence of NaCl ions, or molecular due to

Figure 4. (a) Molecular polarization in a single water molecule. (b) Polarization induced by hydrogen bonds across adjacent water molecules.

Figure 5. Dipole moments per water monomers across hydrogen bonded chains: (a) bifurcated chain (b) transverse hydrogen bonded chain and (c) longitudinal hydrogen bonded chain

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Figure 6. Relative dielectric constant values, κ′, as a function of frequency for calcite samples exposed to various humidity levels. (a) solid, (b) compressed compact of coarse powder A, (c) compact of fine powder B. the additionally dissolved gases O2, N2, CO2, will tend to quantified by: (i) increase of relative dielectric constant at a given frequency, (ii) frequency bandwidth where the polarization is detected, (iii) tanδ increase and related resonance frequency. The above may explain the complex permittivity data obtained for the examined water samples.

C. T. Dervos et al.: Effect of Water on Permittivity of Nanodielectrics Exposed to the Atmosphere 1562

3.2 SOLID SAMPLES IN A HUMID ENVIRONMENT

The electrical properties of solid micro-crystalline and nano-crystalline dielectrics may strongly depend upon the interfacial conditions [16, 17]. For the examined calcite samples the variation of relative dielectric constant with frequency as a function of atmospheric humidity is given in Figure 6. According to these results the κ′ values augment at increased atmospheric humidity levels for all specimen types, i.e. bulk or powders. The phenomenon is more pronounced for

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the powdered compacts (Figures 6b and 6c) compared to the bulk solid samples (Figure 6a). This can be possibly attributed to the greater effective surface area interacting with water molecules in all powdered compacts. Increased κ′ values may come as a result of strong interfacial polarization developing by water absorption. For frequencies below 100 Hz the attached water molecules on the calcite particles dominate the overall permittivity response of the powders. This is attributed to the increased polarizabilities offered by the water molecules and the exceptionally high κ′ values of water at low frequencies as indicated by the experimental data given in Figure 3a. According to the “water shell model” proposed for nanocomposites exposed to a humid environment [18], a few monolayers of water molecules may build-up around the particle cores, in which case their volumes will become electrostatically screened, i.e. all energy applied by an external a.c. electric field will be absorbed by the surface polarization mechanism [2]. The mechanism is reversible, i.e. as the environmental relative humidity drops, the relative dielectric constant reduces towards κ′ values corresponding to lower humidity levels. Therefore, the disks of compressed calcite nano-powders may be utilized as humidity sensors simply by recording κ′ values at low frequencies (i.e. 20 Hz) to maximize signal output efficiency.

The results of Figure 7 point out that under similar humidity levels the dissipation factor (tanδ) values for the solid calcite samples are significantly lower, compared to the powdered calcite compacts. This might be explained by the fact that the powdered materials develop additional interfacial polarization due to the increased specific surface, that tends to intensify losses at low frequencies by water molecule absorption [19]. As the humidity level rises, the water absorption produces additional polarization that is more pronounced for the fine powder B with the smaller particle diameters and the higher specific surface. The developing tanδ peaks at characteristic frequencies can be utilized to monitor polarization-induced effects on the calcite surface by the water absorption. Notice that for the case of the compressed fine powder B, the peaks become more intense and shift towards higher frequencies at increased humidity levels compared to the response obtained for the coarse powder A. Similar response has been attained for all crystalline powders examined. A possible explanation based on the electronic theory of solids might be as follows: Due to the surface adhesion forces developing by polarization charges across the hydrogen bonds water molecules can be attached over the charged surface of a crystalline solid. Figure 8 provides possible models for the attachment of a single water molecule, a monomer, and water oligomers, over positively and negatively charged surfaces of solids. There are various reasons initiating the production of surface charging, the most important being that nano-crystals exhibit a very high surface-state electronic density between interfaces. This is initiated by the fact that the calcite crystal terminates abruptly at the surface interrupting the perfect periodicity of the hexagonal lattice. In this case, solutions of Schrödinger’s equation exist, which correspond to the introduction of energy levels within the forbidden gap of the dielectric, and to imaginary values of the wave vector, k.

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Figure 8. Proposed models describing the effect of water molecule absorption on crystalline nano-particles and the polarization vectors formed across the hydrogen bonds developing between attached water molecules and the charged surface of a nano-dielectric . These wave-functions are evanescent waves, decaying exponentially with depth from the particle surface. They are localized in space (unlike the Bloch waves which propagate through the crystals), and in a perfect micro-crystalline or nano-crystalline particle can only exist around its surface [20]. The full compliment of electrons necessary to make the whole surface electrically neutral, can only be accommodated when the band of surface states is partially filled. This leads to the concept of the “neutral level” Φo, which is the level to which the surface states are filled when the surface is electrically neutral. When states below Φo are empty, the surface has a net positive charge while, if states above Φo are filled, the surface attains a net negative charge [21]. Surface electronic states of crystalline semiconductors follow the Fermi-Dirac statistics and therefore the surface electronic charge redistributes its occupancy levels to attain thermodynamic equilibrium conditions within very short intervals (practically of the order of 10-10 s or less) [21, 22].

3.3 THE EFFECT OF SAMPLE DEHYDRATION

During the fabrication of nano-composite materials the incorporated nano-particles must be free of any surface contaminants (i.e. moisture or other adsorbed gaseous impurities). This may be practically achieved in the dehydration stage of the nano-filler [23]. For the examined nano-powdered compacts two different dehydration methods were exploited: (i) Calcinations at various temperatures and (ii) a high-vacuum drying technique.

The dehydration effect on complex permittivity of Al2O3 powder compacts containing 50%(w) nano-powder is presented by the results of Figure 9. The dehydration has been

applied on the as-received powders which had been exposed to the atmosphere. The compressed powder compacts were inserted in a high-vacuum chamber of 10-4 Pa (10-6 mbar) for a period less than one hour, or alternatively were calcined at 500 °C in a tube furnace in an atmospheric environment. The drawback of calcinations is the increase of grain boundaries due to sintering. As the results of Figure 9 point out, both dehydration methods applied on the hydroscopic Al2O3 powder compacts remove the surface molecular polarization component and reduce relative dielectric constant values by orders of magnitude in the low frequency regime (f <10 kHz). They also eliminate the characteristic peaks of the dissipation factor (tanδ) emerging at approx. 2 kHz due to water molecule absorption and therefore, minimize losses. However, after prolonged re-exposure to the atmosphere (9 days) the vacuum dehydrated samples will re-absorb water molecules at their surfaces and this will again dominate their complex permittivity response, as shown in Figure 9. This phenomenon is not so intense for the calcined specimens possibly due to the particle size growth and agglomerations formed by the sintering process. When the dehydrated samples (either by vacuum or heating) are re-exposed to a humid environment

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Figure 9. (a) Relative dielectric constant vs. frequency. (b) tanδ vs. frequency. Permittivity changes induced on Al2O3 compacts by vacuum drying, calcination and moisture sorption in an atmospheric environment.

their dielectric response increases again, yet it remains less than the corresponding untreated pristine condition. This may be explained by the available number of

C. T. Dervos et al.: Effect of Water on Permittivity of Nanodielectrics Exposed to the Atmosphere 1564

polarizing surface dipoles, i.e. the water molecules forming a shell around the nano-particles [18]. The sites where water molecules can be electrostatically attached on the surface is directly proportional to the product among the electronic surface state density and the surface area. This product may be reduced: (i) by increasing the particle size during calcinations, thus reducing the effective surface area, or (ii) by reconstructing surface atoms bonding schemes, and connecting them chemically to non-polar molecules e.g. CO2, thus reducing the available surface state densities. The reduced numbers of available surface sites that are capable of interacting with the water vapor molecules may lead to the so-called “early saturation effect”, or “ageing”. This mechanism is also observed in microcrystalline sensors (i.e. tin oxide) after several gas sensing cycles. Similar response has been encountered for the TiO2 powder compacts, with the only difference being that moisture intake tends to induce two discrete dissipation factor peaks developing at two different frequencies, one at 800 Hz and the other at 200 kHz approximately, as shown by the results of Figure 10. These could be possibly attributed to the presence of crystals with two different crystal structures, i.e. anatase and rutile, which induce different polarization mobilities of the attached water molecules due to the difference in binding energy of water molecules upon anatase or rutile TiO2 surface.

According to experimental results the thermal dehydration of TiO2 up to 900 °C appeared to be more efficient compared

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Figure 11. Particle-size growth by calcinations at different temperatures. The powder compacts are mixtures of 200nm-500nm anatase TiO2. to the high-vacuum dehydration. This may be concluded by the fact that for the vacuum dried samples the characteristic tanδ peaks are not removed entirely, as shown in Figure 10b. However, it is now known that thermal treatment leads to particle size growth [24] and possibly to phase transitions. Phase transitions may depend on particle size and shape, purity, source effects, atmosphere, reaction or fabrication conditions, particle packing, boundary concentration, or even metal ion doping effects [25-30]. The observed particle size growth for TiO2 powder compacts can be envisaged in the SEM photographs given in Figure 11. Thus, particle size growth and crystal integrity issues are the major concerns related to the dehydration by calcinations. It should be mentioned that workers in the field occasionally perform dehydration of TiO2 particles at even higher temperatures, i.e. 1000 °C for 24 h.

4 CONCLUSIONS As the particle size of an ionic crystal becomes progressively

smaller towards the nanoscale, its polarization properties will have a major surface contribution that will act in synergy with the volume polarization. When exposed to humidity (or other polarizing atmospheric gases) the surface contribution will be strongly intensified and it is expected to dominate all bulk electronic properties of the material. The phenomenon is more intense for lower frequencies (f<1 MHz) where the molecular polarization of water dominates. Even though surface attached molecules may be removed by internal degassing in a high vacuum environment, the phenomenon of surface absorbed polarizing constituents will be reinitiated when the nano-particles are re-exposed to the atmosphere. Thus, the volume of the nanoparticles is electrostatically screened. Calcination leads to more stable surface conditions, in terms of moisture intake effects, but this is rather related to particle size growth, agglomerations due to sintering, or surface oxidation.

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Constantine T. Dervos (M’94) received the B.Sc. degree in electrical engineering from the National Technical University of Athens (NTUA), Greece, in 1980, the M.Sc. in solid state electronics and the Ph.D. in physics and electronics from the University of Manchester Institute of Science and Technology (U.M.I.S.T.), Manchester, UK, in 1982 and 1985, respectively. He is currently a professor in the Department of Information Transmission Systems and

Materials Technology, School of Electrical and Computer Engineering, and a director of the Electrical Materials Laboratory, NTUA. His research activities cover metal semiconductor contacts, electrical contacts, interfacial transport processes, surface physics, material aging and destruction mechanisms, high voltage insulators, dielectrics, and partial discharge diagnostic techniques. Prof. Dervos is a member of the Technical Chamber of Greece and a Fellow of the National Association Relay Manufacturers/EIA.

John A. Mergos was born in Athens, Greece in 1980. He received the Diploma in electrical and computer engineering from the National Technical University of Athens (NTUA), Athens, Greece in 2003 and the Ph.D. degree from the School of Electrical and Computer Engineering, Division of Information Systems and Materials Technology, NTUA. His thesis covered the interaction between solid or gaseous dielectric materials and their environment. His current research activities involve material characterization, including dielectric

spectroscopy, crystal characterization and mass spectrometry. Dr Mergos is a member of the Technical Chamber of Greece.

Panayotis D. Skafidas was born in Kalamata, Greece in l964. He received the B.Sc. degree in electrical engineering from the National Technical University of Athens (NTUA), 1989. He also obtained the Ph.D. degree in electrical engineering from NTUA, 1994. His thesis covered the field of thick-film technology and fabrication techniques of solid-state gas sensors. He is currently employed as a part time teaching assistant in the Laboratory of Electrical Materials, NTUA. His research activities have been focused in the field

of microelectronic materials, thick-film deposition techniques for use in the semiconductor industry, photovoltaics, and insulating materials.

Maria D. Athanassopoulou was born in Athens, Greece in 1980. She received the Diploma in electrical and computer engineering from the National Technical University of Athens (NTUA), Greece, 2007. She is currently working for the Ph.D. degree in materials science at the School of Electrical and Computer Engineering, NTUA. Her research subject is on nano-composite materials and their electrical characterization. Mrs. Athanassopoulou is a member of the Technical Chamber of Greece.

Panayota Vassiliou received the B.Sc. degree in chemical engineering from the University of California, Berkeley in 1975, the M.Sc. and Ph.D. degrees in Chem. Eng. from the School of Chem. Eng., National Technical University of Athens (NTUA), Greece in 1977 and 1981, respectively. She is a Professor in the School of Chemical Engineering, NTUA. She consults on the selection of materials for industrial applications and performs failure analysis after accidental catastrophes.

The main themes of research activities are coating materials, degradation mechanisms, anticorrosive coatings, effects of working conditions on materials and components, effects of acid deposition on historical structures, and restoration of surfaces of monuments. She is responsible for testing materials to be used for the restoration of monuments and especially of the Acropolis of Athens. Prof. Vassiliou is a member of the Technical Chamber of Greece. She is the national representative of Greece in the International Corrosion Council.