Στα πλαίσια της αναζήτησης νέων μεθόδων παραγωγής ενέργειας υψηλής απόδοσης και φιλικής προς το περιβάλλον, ένα μεγάλο μέρος των ερευνητικών δραστηριοτήτων σε διεθνή κλίμακα έχει στραφεί στην ανάπτυξη της τεχνολογίας των κελιών καυσίμου στερεού ηλεκτρολύτη, SOFCs (Solid Oxide Fuel Cells). Ένα από τα μειονεκτήματα που εμφανίζονται κατά την μακρόχρονη λειτουργία ενός ‘state of the art’ κελιού καυσίμου αποτελούμενο από Ni/8YSZ (8 mol% Y2O3 stabilized ZrO2) κεραμομεταλλικό (άνοδος) - 8YSZ (ηλεκτρολύτης) - (La,Sr)MnO3 περοβσκίτη (κάθοδος) - LaCrO3 περοβσκίτη (συνδέτης) είναι η υποβάθμιση της απόδοσής του, η οποία μεταξύ άλλων οφείλεται στην αστάθεια της μικροδομής του κεραμομεταλλικού ηλεκτροδίου της ανόδου στις υψηλές θερμοκρασίες λειτουργίας του, λόγω συσσωμάτωσης της μεταλλικής φάσης. Στόχος της παρούσας εργασίας είναι η ανάπτυξη νέων υλικών με σκοπό την εφαρμογή τους ως ανοδικά ηλεκτρόδια σε κελιά καυσίμου στερεού ηλεκτρολύτη τόσο υψηλών (High Temperature SOFCs, 800-1000oC) όσο και μέσων θερμοκρασιών (Intermediate Temperature SOFCs, 650-800oC). Για το σκοπό αυτό και όσον αφορά τα HT-SOFCs παρασκευάσθηκαν, χαρακτηρίσθηκαν και ελέγχθηκαν οι ιδιότητες μικτών κεραμικών οξειδίων επιλεγμένων συνθέσεων των τριμερών συστημάτων Y2O3-ZrO2-TiO2 (YZT), Y2O3-ZrO2-Nb2O5 (YZN) και Y2O3-ZrO2-CeO2 (YZC) σε σύγκριση με το κεραμικό 8YSZ, ενώ έπειτα από την εξαγωγή των αποτελεσμάτων η έρευνα εστιάσθηκε στα κεραμομεταλλικά υλικά του συστήματος Ni/YZT με προσθήκη 30, 40 και 45 vol% Ni. Tα αποτελέσματα έδειξαν ότι τα Ni/YZT κεραμομεταλλικά συστήματα παρουσιάζουν βελτιωμένη μηχανική συμβατότητα με το στερεό ηλεκτρολύτη. Ο μεταλλογραφικός έλεγχος σε συνδυασμό με ανάλυση εικόνας έδειξε ότι η μικροδομή τους παραμένει σταθερή διατηρώντας τις τιμές της ηλεκτρικής αγωγιμότητας πρακτικά αμετάβλητες μετά από μακροχρόνια έκθεση (1000 h) σε αναγωγική ατμόσφαιρα (Ar/4%H2). Η εν λόγω συμπεριφορά παρουσιάσθηκε πιο ενισχυμένη ιδιαίτερα για τα κεραμομεταλλικά με αυξημένα ποσοστά TiO2 στην κεραμική φάση. Πειράματα διαβροχής σε συστήματα κεραμικών (YZT) σε επαφή με ρευστό Ni έδειξαν ότι η προσθήκη TiO2 βελτιώνει την ισχύ του δεσμού στη διεπιφάνεια μετάλλου/κεραμικού. Ηλεκτροχημικές μετρήσεις σε κελιά καυσίμου με Ni/YZT κεραμομεταλλικές ανόδους έδωσαν ενθαρρυντικά αποτελέσματα, επιτυγχάνοντας για ένα από τα υπό μελέτη συστήματα βελτιωμένη απόδοση σε σύγκριση με τη συμβατική άνοδο, Ni/8YSZ. Όσον αφορά τη δυνατότητα μείωσης της θερμοκρασίας λειτουργίας ενός SOFC από τους 900-1000οC στους 650-800οC και την ανάπτυξη των IT-SOFCs, η έρευνα στράφηκε προς κεραμικές συνθέσεις βασισμένες στο CeO2 και πιο συγκεκριμένα προς τα συστήματα Y2O3-CeO2 (YC) και Y2O3-CeO2-TiO2 (YCT). Ο κρυσταλλογραφικός έλεγχος των κεραμικών κόνεων, μετά από θερμική ανόπτηση μέχρι τους 1400οC στον αέρα, έδειξε ότι η βασική κρυσταλλική τους δομή αντιστοιχεί στο κυβικό πλέγμα του φθορίτη. Στα συστήματα που περιέχουν TiO2 εμφανίζεται ο σχηματισμός μιας επιπλέον φάσης με πυροχλωριτική δομή (Y2Ti2O7). Οι μετρήσεις του συντελεστή θερμικής διαστολής (TEC) στον αέρα στη θερμοκρασιακή περιοχή 25-1000°C έδωσε παρεμφερείς τιμές μειούμενες με αυξανόμενο το ποσοστό σε Ti. Σε ατμόσφαιρα Ar/4%H2 οι τιμές του TEC αυξάνονται σημαντικά για θερμοκρασίες T ≥ 800°C. Οι απόλυτες τιμές της συνολικής ηλεκτρικής αγωγιμότητας των κεραμικών σε αναγωγικές συνθήκες (Ar/4%H2) στη θερμοκρασιακή περιοχή 450-900°C εμφανίζονται σημαντικά υψηλότερες συγκριτικά με τις αντίστοιχες τιμές στον αέρα λόγω του μικτού ιοντικού-ηλεκτρονικού της χαρακτήρα. Οι απόλυτες τιμές της ιοντικής αγωγιμότητας παρουσιάζονται σημαντικά ενισχυμένες, περίπου μισή τάξη μεγέθους σε σχέση με τις αντίστοιχες του 8YSZ, για τις κεραμικές συνθέσεις του συστήματος Y0.20Ce0.80-xTixO1.9 με τις χαμηλότερες περιεκτικότητες σε Ti. Τα αντίστοιχα Ni-cermets με υψηλά ποσοστά σε ύττρια και χαμηλά ποσοστά σε τιτάνια στην κεραμική φάση επέδειξαν εξαιρετική μακροχρόνια σταθερότητα της ηλεκτρικής αγωγιμότητας, ενώ υπό τις συνθήκες λειτουργίας ενός SOFC (~900οC) η διάχυση του Ce προς το στερεό ηλεκτρολύτη 8YSZ είναι αμελητέα. / In the frame of research for the development of alternative, friendly to the environment methods for the production of energy, significant effort is focusing on SOFC (Solid Oxide Fuel Cell) technology. This work aims to the development of new promising materials for their application as anode electrodes in solid oxide fuel cells operating at high temperatures (HT-SOFCs), as well as at the intermediate temperature range (IT-SOFCs). Concerning the HT-SOFCs, mixed ZrO2-based ceramic oxides of the ternary systems Y2O3-ZrO2-TiO2 (YZT), Y2O3-ZrO2-Nb2O5 (YZN) and Y2O3-ZrO2-CeO2 (YZC) were prepared, characterized and studied in terms of thermal expansion and electrical properties, as well as their potential application as the ceramic components in the anode cermet material of a SOFC, focusing on the Ni/YZT system containing 30, 40 and 45 vol% Ni. The results showed that Ni/YZT cermets exhibit improved mechanical adjustment with the solid electrolyte and enhanced structural stability compared to Ni/8YSZ while the values of the electrical conductivity remain practical constant after long-term annealing at 1000oC for up to 1000 h in reducing atmosphere (Ar/4%H2), especially for the cermets with high TiO2-content in the ceramic phase. Wetting experiments in the system of YZT ceramics in contact with Ni showed that TiO2 presence enhances the bond strength at the metal/ceramic interface, which results in the decrease of the agglomeration tendency of the metallic particles. Electrochemical tests performed on fuel cells with Ni/YZT anode cermets showed encouraging results, whereas it is remarkable that for a specific composition was achieved improved performance compared to Ni/8YSZ anode. With regard to the possible reduction of the operating temperature from 900-1000oC to 650-800°C and the development of IT-SOFCs, the study was focused on CeO2-based oxides and more specifically on the binary Y2O3-CeO2 (YC) and ternary Y2O3-CeO2-TiO2 (YCT) systems. The XRD analysis of the ceramic powders after heating at temperatures up to 1400°C in air showed the formation of the cubic fluorite structure for the YC ceramic, whereas for the YCT ceramics an additional phase (Y2Ti2O7) with pyrochlore structure was formed. The thermal expansion coefficient (TEC) of the ceramics measured in air between 25 and 1000°C gave comparable values, decreasing with increasing Ti content, while in Ar/4%H2 atmosphere the TEC values of the ceramics increase dramatically at T ≥ 800 °C. The absolute values of the total electrical conductivity of the ceramics measured between 450-900°C in Ar/4%H2 increase significantly compared to those measured in air, due to their mixed conducting ionic-electronic character. The ionic conductivity of the Y0.20Ce0.80-xTixO1.9 ceramics with low amounts of Ti, measured in air, is appeared strongly increased, by about half order of magnitude, compared to 8YSZ. The corresponding Ni-cermets with high amounts of yttria and low amounts of titania in the ceramic phase exhibit improved long-term stability of the electrical conductivity, while under the operating conditions of a SOFC (~ 900oC) no detectable diffusion of Ce4+ in the 8YSZ electrolyte was observed.

The assembly of nanostructures into “multi”-dimensional materials is one of the main topics occurring in nanoscience today. It is now possible to produce high quality nanostructures reproducibly but for their further application larger structures that are easier to handle are required. Nevertheless during their assembly their nanometer size and accompanying properties must be maintained. This challenge was addressed in this work. Lead chalcogenides have been chosen as an example system because they are expected to offer great opportunities as thermoelectric materials. Three different ways to achieve assemblies of lead chalcogenide nanostructures were used and the resulting structures characterized with respect to their potential application as thermoelectric material. The first means by which a “multi”-dimensional assembly of lead chalcogenide quantum dots can be produced is the formation of porous structures such as aerogels and xerogels. A procedure, where the addition of an initiator such as oxidizers or incident radiation is unnecessary, is introduced and the formation process studied by absorption spectroscopy. The time-consuming aggregation step could be significantly reduced by employing a slightly elevated temperature during gelation that does not lead to any observable differences within the resulting gel structures. After either supercritical or subcritical drying, highly porous monolithic gel structures can be achieved. During the gel formation the size and the shape of the particles changed and they were directly linked together. Nevertheless the resulting porous structures remain crystalline and size dependent effects of the optical properties could be shown. Gels produced from a mixture of PbS and PbSe QDs show a homogenous distribution of both materials but it is not clear to what extent they form an alloy. Although the particles are directly linked together the resulting porous structures possess a very high resistivity and so it was not possible to characterize the semiconductor aerogels with regard to their thermoelectric properties. To achieve an enhanced conductivity porous structures containing PbS and Au nanoparticles have been produced. As has been seen for the pure semiconductor gels the size of the PbS quantum dots has increased and elongated particles were formed. In contrast to the PbS QDs the Au nanoparticles did not change their size and shape and are unevenly distributed within the PbS network. Through the use of the gold nanoparticles the conductivity could be increased and although the conductivity is still quite small, it was possible to determine Seebeck coefficients near room temperature for a mixed semiconductor-metal gel. The second means by which QD solids could be formed was by the compaction of the QD building blocks into a material that is still nanostructured. Therefore the synthesis of PbS was optimized to achieve sufficient amounts of PbS quantum dots. The ligands used in the synthesis of the QDs unfortunately act as an insulating layer resulting in QD solids with resistivities as high as 2 Gigaohm. For this reason different surface modification strategies were introduced to minimize the interparticle distance and to increase the coupling between the QDs so as to increase the conductivity of the resulting quantum dot solids. One very promising method was the exchange of the initial ligands by shorter ones that can be destroyed at lower temperatures. By such heat treatments the resistivity could be decreased by up to six orders of magnitude. For the pressing of the quantum dots two different compaction methods (SPS and hydraulic pressing) were compared. While the grain growth within the SPS pressed samples is significantly higher the same densification can be achieved by a cold hydraulic pressing as well as by SPS. The densification could be further increased through the use of preheated PbS QDs due to the destruction of the ligands. Samples which had been surface modified with MPA and subsequently thermally treated show the best results with respect to their thermopower and resistivities. Nevertheless the conductivity of the QD solids is still too high for them to be used as efficient thermoelectric materials. The final assembly method does not involve QDs but instead with one dimensional nanowires. Therefore a synthesis was developed that enables the formation of PbS nanowires of different diameters and one that is easy up-scalable. By the use of a less reactive sulfur precursor and an additional surfactant the formation of nuclei is significantly retarded and within an annealing time of two hours nanowires can be formed presumably by an oriented attachment mechanism. Single crystalline nanowires with a diameter of 65-105 nm could be achieved with the longest axes of the nanowires being parallel to [100]. The resulting nanowires were used as building blocks for film formation on glass substrates by an easily implemented method that requires no special equipment. To characterize the films with a view to their possible application as a thermoelectric material, surface modifications of the films were performed to improve the charge transfer in the films and the Seebeck coefficients of the resulting films measured. Therefore the previous approach of using MPA was applied and a subsequent thermal treatment demonstrated very promising results. In addition an crosslinking ligand was used for surface treatment that leads to similar results as was observed for the thermally treated MPA approach. Both approaches lead to an order of magnitude decrease in the resistivity and due to the fewer grain boundaries present in the films composed of nanowires as compared to the QD assemblies the conductivity is significantly higher. The Seebeck coefficient measurements show that the thermal treatment only slightly affects the Seebeck coefficients. Therefore a significantly higher power factor could be achieved for the nanowire films than for the QD solids.

<p>One of the most powerful aspects of conducting polymers is their ability to be nanostructured through innovative, synthetically manipulated, transformations, such as to tailor-make the polymers for specialized applications. In the exponentially increasing wide field of nanotechnology, some special attention is being paid to innovative hybrid dendrimer-core based polymeric smart materials. Star copolymers are a class of branched macromolecules having a central core with multiple linear polymer chains extending from the core. This intrinsic structural feature yields a unique 3D structure with extended conjugated linear polymer chains, resulting in star copolymers, which have higher ionic conductivities than their corresponding non-star conducting polymer counterparts. In this study an in-depth investigation was carried out into the preparation and characterization of specialized electronic &lsquo / smart materials&rsquo / . In particular, the preparation and characterization of novel conducting dendrimeric star copolymers which have a central poly(propylene imine) (PPI) dendrimer core with conducting polypyrrole (PPy) chains extending from the core was carried out. This involved, first, the preparation of a series of dendrimeric polypyrrole poly(propylene imine) star copolymers (PPI-co-PPy), using generations 1 to 4 (G1 to G4) PPI dendrimer precursors. The experimental approach involved the use of both chemical and electrochemical synthesis methods. The basic procedure involved a condensation reaction between the primary amine of a diamino functional PPI dendrimer surface and 2-pyrrole aldehyde, to afford the pyrrole functionalized PPI dendrimer (PPI-2Py). Polymerization of the intrinsically contained monomeric Py units situated within the dendrimer backbone was achieved via two distinctly different routes: the first involved chemical polymerization and the second was based on potentiodynamic oxidative electrochemical polymerization. The star copolymers were then characterized using various sophisticated analytical techniques, in-situ and ex-situ. Proton nuclear magnetic resonance spectroscopy (1HNMR) and Fourier transform infrared spectroscopy (FTIR) were used to determine the structures. Scanning electron microscopy (SEM) was used to determine the morphology. Themogravimetric analysis (TGA) was used to study the thermal stability of the prepared materials. X-ray diffraction analysis (XRD) was used to study the structural make-up of phases, crystallinity and amorphous content. Hall effect measurements were carried out to determine the electrical conductivity of the chemically prepared star copolymers. The PPI-co-PPy exhibited improved thermal stability compared to PPI-2Py, as confirmed by TGA. SEM results showed that the surface morphology of the functionalized dendrimer and star copolymer differed. The surface morphology of the chemically prepared star copolymers resembled that of a flaky, waxy material, compared to the ordered morphology of the electrochemically grown star copolymers, which resembled that of whelk-like helixes. In the case the electrochemically grown star copolymers, SEM images recorded at higher magnifications showed that the whelk-like helixes of the star copolymers were hollow tubes with openings at their tapered ends, and had an average base diameter of 2.0 &mu / m. X-ray diffraction analysis of the first generation star copolymer G1PPI-co-PPy revealed a broadly amorphous structure associated with PPy, and crystalline peaks for PPI. Cyclic voltammetry (CV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) techniques were used to study and model the electrochemical reactivity of the star copolymer materials. Electrochemical impedance spectroscopy data showed that the G1PPI-co-PPy exhibited slightly higher ionic conductivity than pristine PPy in lithium perchlorate. The second generation star copolymer G2PPI-co-PPy electrochemically deposited on a platinum (Pt) electrode had a lower electrochemical charge transfer resistance compared to electrodeposited polypyrrole (PPy) on a Pt electrode, and bare Pt. The decrease in charge transfer resistance was attributed to an increase in the conjugation length of the polymer as a result of the linking of the highly conjugated PPy to the PPI dendrimer. Bode impedimetric analysis indicated that G2PPI-co-PPI was a semiconductor, with a maximum phase angle shift of 45.3&deg / at 100 MHz. The star copolymer exhibited a 2- electron electrochemistry and a surface coverage of 99%. Results of Hall effect measurements showed that the star copolymer is a semiconducting material, having a conductivity of 0.7 S cm-1, in comparison to the 1.5 S cm-1 of PPy. To the best of my knowledge, these new star copolymers have not been reported in the open literature. Their properties make them potentially applicable for use in biosensors.</p>

Chromium is used in many processing applications, which has led to the formation of chromium(VI) waste. Cr(VI) is an unstable, mobile carcinogen, which is interchangeable with Cr(III) under certain environmental conditions. Management of this waste, however, is often not considered. Mine under investigation is an example of such historic mismanagement. During the second World War, Cr(VI) waste was transferred to the study site from areas where leather products were made for the war effort. This waste was not managed appropriately in the past and with time Cr(VI) leached into the groundwater and possibly surface water resources. As these water resources are used for domestic and agricultural water supply, this may have serious effects on the human and environmental health in the area. Some of the major Cr(VI) effects on human and animal health include malignant tumours, skin irritation, respiratory and reproductive system damage. Lung cancer is of concern when Cr(VI) is inhaled and stomach tumours occur when this chemical pollutant is ingested. The effects of Cr(VI) on plants include the disruption of shoot and root elongation, and if it accumulates enough within the plant can cause ingested health problems for humans and animals. Water quality guidelines state that the Target Water Quality Range for Cr(VI) in drinking water should not exceed 0.05 mg/L. Prolonged exposure of values higher than this target value has adverse health effects and may result in cancer. The study site has a scarcity in water sources and therefore requires good quality water resources. This study aims to identify and use biomarkers to assist in the hydrological characterization of the mine. Available mitigation options can be implemented once it is known how the water in the area moves and distributes Cr(VI) pollution. A biomarker is an indicator of a biological state, which in turn can be used to assist in characterizing the chemical conditions of the sub-surface. Bacteria can aid as environmental biomarkers as they are sensitive and specific to the environmental conditions in which they flourish. In this way they give a good indication of the environmental condition and any possible pollution. Due to the fact that ground- and surface water are integrated resources, it is likely that if one is impacted by pollution, it will indirectly impact the other one. Therefore, the biomarkers identified can be used to characterize water pollutants that are present in ground- and some surface water resources. A description of the study site is provided, wherein the climate, elevation, geology, land use, geohydrology, hydrochemistry and surface water are documented. These factors help to identify and clarify the sources and pathways that water and the pollution would follow. Ten water samples, from surface and groundwater, were obtained in two separate sampling opportunities. The first analysis of the water samples included the determination of the chemical constituents. Two of these constituents analyzed were the total Cr and individual Cr(VI) levels. Six water samples had excessively high Cr values (exceeding the Water Quality Target Range of drinking water and water agricultural use). These values ranged from 0.1 – 3.9 mg/L. The 6 samples with excessive Cr(VI) values were used for the microbial analyses. The microbial analyses consisted of DAPI (4’,6-diamidino-2-phenylindole ) staining, for cell enumeration, and molecular analyses. The molecular analyses included polymerase chain reaction (PCR), denaturing gradient gel electrophoresis (DGGE) and sequencing applications concluded in the laboratory. Fifteen bands, representing different organisms, were removed from the DGGE polyacrylamide gel and processed for sequencing. The organisms that were present in the sample were uncultured Cyanobacterium, Sediminibacterium salmoneum, uncultured Bacteroidetes bacterium, uncultured betaproteobacterium, uncultured actinobacterium, uncultured Rhodocyclaceae, uncultured Chloroflexi bacterium and uncultured delta-proteobacterium. According to literature most of these organisms may adapt the ability to either reduce Cr(VI) or resist any effect of Cr(VI) in the environment. Two of the bands were highly unidentified organisms, which means that these organisms have not yet been cultured or identified in any sense. The reason for this is that most microorganisms have not yet been documented. This also makes it difficult to identify the exact bacterial strain present within the samples. The deoxyribonucleic acid (DNA) sequences of the different organisms were very different from each other, when compared by a dendrogram. This means that there was a diverse community present within the samples. Electrical conductivity profiles were conducted in the monitoring boreholes to identify possible fracture positions. The total chromium and chromium(VI) levels were documented and compared. Other chemical factors were analysed and those of high value, such as chloride, nitrate and chromium measurements, were used for statistical analyses and comparison with the biomarkers present in the sample. A positive correlation was found between the sample sites and the organisms present within each. It was noted that different communities have different metabolic activities related to susceptibility and will therefore differ under specific environmental conditions. The microorganisms that were present in the 6 water samples all have the ability to either resist or reduce Cr(VI). This means that in Cr(VI) polluted areas they are more likely to flourish than organisms that do not possess this ability. Such susceptible, non-resistant organisms would otherwise occur naturally in a non-polluted environment. From the obtained results it was noted that microorganisms could aid as biomarkers when determining the environmental condition (with respect to Cr(VI) pollution). The bacteria analysed in the samples all indicate a level of chromium pollution, and aided in the determination of pollution sources. These biomarkers can therefore be used to determine the location of other chromium deposits not yet located. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2013

Chromium is used in many processing applications, which has led to the formation of chromium(VI) waste. Cr(VI) is an unstable, mobile carcinogen, which is interchangeable with Cr(III) under certain environmental conditions. Management of this waste, however, is often not considered. Mine under investigation is an example of such historic mismanagement. During the second World War, Cr(VI) waste was transferred to the study site from areas where leather products were made for the war effort. This waste was not managed appropriately in the past and with time Cr(VI) leached into the groundwater and possibly surface water resources. As these water resources are used for domestic and agricultural water supply, this may have serious effects on the human and environmental health in the area. Some of the major Cr(VI) effects on human and animal health include malignant tumours, skin irritation, respiratory and reproductive system damage. Lung cancer is of concern when Cr(VI) is inhaled and stomach tumours occur when this chemical pollutant is ingested. The effects of Cr(VI) on plants include the disruption of shoot and root elongation, and if it accumulates enough within the plant can cause ingested health problems for humans and animals. Water quality guidelines state that the Target Water Quality Range for Cr(VI) in drinking water should not exceed 0.05 mg/L. Prolonged exposure of values higher than this target value has adverse health effects and may result in cancer. The study site has a scarcity in water sources and therefore requires good quality water resources. This study aims to identify and use biomarkers to assist in the hydrological characterization of the mine. Available mitigation options can be implemented once it is known how the water in the area moves and distributes Cr(VI) pollution. A biomarker is an indicator of a biological state, which in turn can be used to assist in characterizing the chemical conditions of the sub-surface. Bacteria can aid as environmental biomarkers as they are sensitive and specific to the environmental conditions in which they flourish. In this way they give a good indication of the environmental condition and any possible pollution. Due to the fact that ground- and surface water are integrated resources, it is likely that if one is impacted by pollution, it will indirectly impact the other one. Therefore, the biomarkers identified can be used to characterize water pollutants that are present in ground- and some surface water resources. A description of the study site is provided, wherein the climate, elevation, geology, land use, geohydrology, hydrochemistry and surface water are documented. These factors help to identify and clarify the sources and pathways that water and the pollution would follow. Ten water samples, from surface and groundwater, were obtained in two separate sampling opportunities. The first analysis of the water samples included the determination of the chemical constituents. Two of these constituents analyzed were the total Cr and individual Cr(VI) levels. Six water samples had excessively high Cr values (exceeding the Water Quality Target Range of drinking water and water agricultural use). These values ranged from 0.1 – 3.9 mg/L. The 6 samples with excessive Cr(VI) values were used for the microbial analyses. The microbial analyses consisted of DAPI (4’,6-diamidino-2-phenylindole ) staining, for cell enumeration, and molecular analyses. The molecular analyses included polymerase chain reaction (PCR), denaturing gradient gel electrophoresis (DGGE) and sequencing applications concluded in the laboratory. Fifteen bands, representing different organisms, were removed from the DGGE polyacrylamide gel and processed for sequencing. The organisms that were present in the sample were uncultured Cyanobacterium, Sediminibacterium salmoneum, uncultured Bacteroidetes bacterium, uncultured betaproteobacterium, uncultured actinobacterium, uncultured Rhodocyclaceae, uncultured Chloroflexi bacterium and uncultured delta-proteobacterium. According to literature most of these organisms may adapt the ability to either reduce Cr(VI) or resist any effect of Cr(VI) in the environment. Two of the bands were highly unidentified organisms, which means that these organisms have not yet been cultured or identified in any sense. The reason for this is that most microorganisms have not yet been documented. This also makes it difficult to identify the exact bacterial strain present within the samples. The deoxyribonucleic acid (DNA) sequences of the different organisms were very different from each other, when compared by a dendrogram. This means that there was a diverse community present within the samples. Electrical conductivity profiles were conducted in the monitoring boreholes to identify possible fracture positions. The total chromium and chromium(VI) levels were documented and compared. Other chemical factors were analysed and those of high value, such as chloride, nitrate and chromium measurements, were used for statistical analyses and comparison with the biomarkers present in the sample. A positive correlation was found between the sample sites and the organisms present within each. It was noted that different communities have different metabolic activities related to susceptibility and will therefore differ under specific environmental conditions. The microorganisms that were present in the 6 water samples all have the ability to either resist or reduce Cr(VI). This means that in Cr(VI) polluted areas they are more likely to flourish than organisms that do not possess this ability. Such susceptible, non-resistant organisms would otherwise occur naturally in a non-polluted environment. From the obtained results it was noted that microorganisms could aid as biomarkers when determining the environmental condition (with respect to Cr(VI) pollution). The bacteria analysed in the samples all indicate a level of chromium pollution, and aided in the determination of pollution sources. These biomarkers can therefore be used to determine the location of other chromium deposits not yet located. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2013

In September 2008 Hurricane Ike hit the Texas Gulf Coast with a force stronger than the category 2 storm at which it was rated. With a 3.8 m (12.5 ft) storm surge, the agricultural industry in the area was devastated. The goal of this research was to determine the length of time required to reduce the salt levels brought by the storm surge to near pre-hurricane levels. To do this, four sets of samples were taken across two years and analyzed for salinity using the saturated paste extract method. The initial salt levels in November 2008 had an electrical conductivity (ECe) of the inundated soils as high as 26.7 dS/m. Fifty-four percent of the soils sampled in the 0-15 cm horizons and 9% in the 15-30 cm horizons of the edge area had an ECe >= 4 dS/m. In the surge area 79% of the soils sampled in the 0-15 cm horizons and 30% in the 15-30 cm horizons had an ECe >= 4 dS/m. In April 2009, 38% of the soils sampled in the 0-15 cm horizons and 13% in the 15-30 cm horizons of the edge area had an ECe >= 4 dS/m. In the surge area 71% of the soils sampled in the 0-15 cm horizons and 39% in the 15-30 cm horizons had an ECe >= 4 dS/m. By December 2009, none of the soils sampled in the edge area had an ECe >= 4 dS/m. In the surge area 21% of the soils sampled in the 0-15 cm horizons and 33% in the 15-30 cm horizons had an ECe >= 4 dS/m. By October 2010, all soils sampled had leached sufficient salts to be classified as non-saline to very slightly saline soils. Utilizing the November 2008 data set, 28 random samples were selected for exchangeable Na percent (ESP) in order to develop the ESP-SAR (Na adsorption ratio) predictive equation, ESP= 1.19(SAR)^0.82. The SAR-ESP relationship is statistically significant (95% confidence level), with a correlation coefficient of 0.964 (df=26).

Fabrication of SWCNT-PMMA and Activated Charcoal- PMMA composites was carried out by the compression moulding technique. Then Mechanical and Electrical properties of the composites were investigated. The morphological studies of composites showed a) good dispersion of fillers and b) good interaction between fillers and matrix. Electrical conductivity of SWCNT-PMMA composites was increased by 9 orders of magnitude (at 0.8 % volume fraction of SWCNT) and that of AC-PMMA composites increased by 16 orders of magnitude (at 17 % volume fraction of AC). The percolation threshold of both composites turned out to be lower compared to the theoretical values. A significant improvement in mechanical properties was obtained ??? particularly in AC-PMMA composites which showed a 400 % improvement in Vickers microhardness ??? raising the polymer matrix abrasion property literally to that of Aluminium alloys (Dobrazanski et al 2006). In conclusion, it is to be noted that Activated Charcoal - PMMA composites have a great potential for cost effective conducting polymer composite production by the use of cheap filler: In addition, the compression moulding technique shows good potential for cost effective fabricating technique for amorphous polymers with high electrical and mechanical properties.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2007. / Härtill 4 uppsatser.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / The aim of this work was to determine criteria for management of nutrient solution in the production of runner tips for producing strawberry plug plants and parsley and chives for commercial mixed bunches. Two experiments were carried out at Departamento de Fitotecnia-UFSM using 2.5 dm3 polypropylene pots filled with sand, placed over 0.8m heigh benches and fertigated by drippers. The first experiment was conducted from 13 October 2011 to 10 April 2012, using strawberry mother plants cv. Camino Real and Oso Grande. Plants were fertigated by five electrical conductivities, 0.4, 0.8, 1.2, 1.6 and 2.0 dS m-1, respectively, in a (5 x 2) completely randomized factorial experimental design. Runner tips emitted by mother plants were collected weekly and counted, being discarded those necrotic. It was determined the number of leaves, crown diameter and dry mass. Runner tips from mother plants of each treatment were rooted in polystyrene trays for plug plants production. Forty five days later, crown diameter, number of expanded leaves and shoot and root dry weight of plug plants were determined. At the end of the experiment, mother plants of each treatment were also collected for dry mass determination of plant organs. The second experiment was conducted from September 12 to October 22, 2012, comparing five electrical conductivities of the nutrient solution, 0.5; 1.5; 2.0; 2.5 and 3.0 dS m-1, respectively, and eight cropping arrays. The arrays were formed by planting side by side in each pot transplants of parsley and chives from one cell of the commercial tray (1S+1C), from two cells of parsley and one of chives (2S+1C), one of parsley and two of chives (1S+2C), two of parsley and two of chives (2S+2C) and four monocropping arrays as controls: seedlings from one cell tray of parsley (1S) and one of chives (1C) and two of parsley (2S) and two of chives (2C) per pot. It was used a (5 x 8) completely randomized factorial experimental design. At the end of the experiment, plants of both species were harvested, separated and fresh (MVPA) and dry mass (MSPA) of shoot were determined. It was concluded that electrical conductivities of the nutritive solution in the range between 0.8 and 1.1 dS m-1 for growing strawberry mother plants lead to higher runner tips and plug plants production. Intercropped parsley and chives can be grown using the same nutrient solution at 2.0 dS m-1 for the commercial production of mixed bunches, while an electrical conductivity of 1.6 dS m-1 can be used for monocropped chives production. / O objetivo deste trabalho foi determinar critérios de manejo da solução nutritiva na produção de pontas de estolões para a produção de mudas de morangueiro e de salsa e cebolinha para produção de maços comerciais mistos. Dois experimentos foram realizados no Departamento de Fitotecnia da UFSM em dispositivos formados por bancadas de 0,8 m de altura com vasos de polipropileno de 2,5 dm3 preenchidos com areia e fertirrigados por fitas gotejadoras. O primeiro experimento foi realizado no período de 13 de outubro de 2011 a 10 de abril de 2012, com plantas matrizes de morangueiro das cultivares Camino Real e Oso Grande. As plantas foram fertirrigadas com cinco condutividades elétricas, 0,4; 0,8; 1,2; 1,6 e 2,0 dS m-1, respectivamente, em esquema fatorial (5 x 2) e delineamento inteiramente casualisado. As pontas de estolões emitidas pelas plantas matrizes foram coletadas semanalmente e contadas, sendo descartadas aquelas necrosadas. Foram determinados o número de folhas, o diâmetro de coroa e a massa seca. Pontas de estolões oriundas das plantas matrizes de cada tratamento foram enraizadas em bandejas de poliestireno para produção de mudas com torrão. Aos 40 dias após o enraizamento, foi determinada a taxa de formação de mudas e o diâmetro de coroa, número de folhas expandidas e massa seca da parte aérea e raízes dessas mudas. Ao final do experimento, foram coletadas também plantas matrizes de cada tratamento para determinação da massa seca dos diferentes órgãos. O segundo experimento foi realizado de 12 de setembro a 22 de outubro de 2012, no qual foram comparadas cinco condutividades elétricas, 0,5; 1,5; 2,0; 2,5 e 3,0 dS m-1, respectivamente, e oito arranjos de cultivo. Os arranjos foram formados pelo plantio lado a lado em cada vaso de mudas de salsa e de cebolinha provenientes de um alvéolo das bandejas comerciais (1S+1C); de dois alvéolos de salsa e um alvéolo de cebolinha (2S+1C); de um de salsa e dois de cebolinha (1S+2C); de dois de salsa e dois de cebolinha (2S+2C) e quatro sistemas de cultivos solteiros considerados testemunhas: mudas de um alvéolo de salsa (1S) e um de cebolinha (1C) e dois de salsa (2S) e dois de cebolinha (2C) por vaso. Foi empregado um esquema fatorial (5 x 8) em delineamento DIC. No final do experimento, as plantas de cada uma das duas espécies foram separadas e foi determinada a massa verde (MVPA) e seca (MSPA) da parte aérea. Concluiu-se que condutividades elétricas da solução nutritiva entre 0,8 e 1,1 dS m-1 possibilitam maior produção de pontas de estolões de morangueiro e formação de mudas com torrão. No cultivo consorciado de salsa e cebolinha, é possível o uso de uma mesma solução nutritiva com 2,0 dS m-1 para a formação de maços mistos, podendo a mesma solução ser empregada também no cultivo da salsa solteira. No cultivo solteiro de cebolinha, a C.E de 1,6 dS m-1 deve ser empregada.

Les alliages conducteurs à haute tenue mécanique sont utilisés dans de nombreux domaines tels que le transport, l’énergie et l’industrie électronique. La demande en ces matériaux est croissante. Les alliages Cu-Be constituent à l’heure actuelle les matériaux conducteurs les plus résistants mais posent un problème de toxicité et de coût. Pour proposer une alternative à ces derniers, nous avons étudié des alliages Cu-Mg hypo-eutectiques. Deux voies de synthèse ont été utilisées afin d’obtenir des composites endogènes possédant une combinaison originale de propriétés structurelles et fonctionnelles : le refroidissement conventionnel et la solidification rapide par melt-spinning. Les microstructures obtenues ont en commun la présence d’agrégats eutectiques et diffèrent principalement par la dimension des paramètres métallurgiques tels que la taille de grains et la distance interlamellaire. Les systèmes présentent des forces motrices de transformation de phases importantes conduisant à une précipitation au cours d’un maintien thermique. L’investigation des propriétés mécaniques et électriques des alliages Cu-Mg montre que ces dernières égalent celles des alliages Cu-Be. En complément de l’approche expérimentale, nous avons adapté deux modèles : un modèle thermocinétique pour décrire l’évolution temporelle de la microstructure qui a lieu à haute température et un modèle mécanique permettant de rationaliser l'influence des paramètres microstructuraux sur les propriétés mécaniques et électriques. / Copper-based high strength conductive alloys are used in a myriad of applications such as transport, energy and electronic industries. The demand for these materials is booming. The strongest conductive alloy is based on the Cu-Be system which has the disadvantage of toxicity and cost. In an attempt to find an alternative to these, we have developed hypoeutectic Cu-Mg alloys. Two synthesis routes were applied to produce endogenous compounds with a unique combination of structural and functional properties: the conventional cooling and the rapid solidification by melt-spinning. The obtained microstructures share the presence of eutectic aggregates and differ mainly by the size of the metallurgical parameters such as grain size and interlamellar distance. The two systems provide high driving forces for phase transformations leading to precipitation during aging. The investigation of the mechanical and electrical properties of Cu-Mg alloys shows that they are equal to those of the Cu-Be alloys. In addition to experimental approach, we have adapted two models: a thermo-kinetic one to describe time evolution of the microstructure which takes place at high temperature and a mechanical one to rationalize the influence of microstructural parameters on mechanical and electrical properties.