In this study, electrically conductive coating materials composed of epoxy resin and carbon black (CB) were prepared by applying two different mixing techniques (Grinding and Mechanical Mixing). The effect of carbon black addition, ultrasonication, mixing type and surface modification of carbon black on the morphologies, electrical and mechanical properties of the composites were investigated. According to test results, Grinding Method is much more efficient and for this method, percolation concentration was found as 2 vol %. The electrical resistivity value obtained at this composition is around 107 ohm.cm. Also, for the samples prepared by Grinding Method, the hardness increased by adding conductive filler, but the impact energy and adhesive strength decreased with increasing carbon black content. Ultrasonication was applied to the samples containing 2 vol % CB obtained by Grinding Method to reduce the electrical resistivity further. Three different ultrasonic mixing times were tried, however, no positive effect was observed on electrical and mechanical properties. Since the addition of carbon black has a negative effect on the processability of the mixture, it was aimed to obtain desired conductivity value at lower percolation concentration by modifying carbon black surface with different silane coupling agents and formamide. The best result in terms of electrical conductivity was obtained for the materials produced with formamide treated carbon black by Grinding Method. At 1 vol % concentration, the electrical resistivity was found as approximately 106 ohm.cm which is three orders smaller than the resistivity of materials prepared with untreated carbon black.

The aim of this study was to improve electrical properties of conductive polymer composites. For this purpose, various studies were performed using different materials in this dissertation. In order to investigate the effect of alternative composite preparation methods on electrical conductivity, nylon 6/carbon black systems were prepared by both in-situ polymerization and melt-compounding techniques. When compared with melt compounding, in-situ polymerization method provided enhancement in electrical conductivity of nylon 6 composites. Furthermore, it was aimed to improve electrical conductivity of polymer composites by modifying surface chemistry of carbon black. 1 wt. % solutions of 3-Aminopropyltriethoxysilane and formamide were tried as chemical modifier, and treated carbon black was melt mixed with low-density polyethylene (LDPE) and nylon 6. According to electron spectroscopy for chemical analysis (ESCA), chemicals used for surface treatment may have acted as doping agent and improved electrical conductivity of polymer composites more than untreated carbon black did. Formamide was more effective as dopant compared to the silane coupling agent. In order to investigate electromagnetic interference (EMI) shielding effectiveness and dielectric properties of conductive polymer composites, 1, 2 and 3 wt. % solutions of formamide were tried as chemical modifier and treated carbon black was melt mixed with poly(ethylene terephthalate) (PET). Composites containing formamide treated carbon black exhibited enhancement in electrical conductivity, EMI shielding effectiveness and dielectric constant values compared to composites with untreated carbon black. In order to enhance electrical conductivity of polymer composites, the selective localization of conductive particles in multiphase polymeric materials was aimed. For this purpose, carbon nanotubes (CNT) were melt mixed with polypropylene (PP)/PET. Grinding, a type of solid state processing technique, was applied to PP/PET/CNT systems to reduce the average domain size of blend phases and to improve interfacial adhesion between these phases. Grinding technique exhibited improvement in electrical conductivity and mechanical properties of PP/PET/CNT systems at low PET compositions. To investigate application potential of conductive polymer composites, polyaniline (Pani)/carbon nanotubes (CNT) composites were synthesized and electrochemical capacitance performances of these systems, as electrode material in electrochemical capacitors, were studied. Polyaniline/carbon nanotubes composites resulted in a higher specific capacitance than that of the composite constituents. Pseudocapacitance behavior of Pani might contribute to the double layer capacitance behavior of nanotubes. Additionally, as an alternative to Pani/CNT systems, polyaniline films were deposited on treated current collectors and electrochemical capacitance performances of these electrode systems were investigated. The highest specific capacitance of polyaniline/carbon nanotubes composites was 20 F/g and this value increased to 35.5 F/g with polyaniline film deposited on treated current collector.

No description available.

Traditional in-situ soil compaction monitoring methods are often limited in their application, thus quality control of compacted fills and roadway embankments remains a challenging problem. As a result, new methods are being developed to more accurately measure in-situ compaction parameters. Time domain reflectometry (TDR) is one such method. Several advances have been made over the past few years to further the use of TDR technology in water content and density measurement of compacted fill. The one-step method relies on the measurement of the apparent dielectric constant in conjunction with the bulk electrical conductivity, and correlates them through two soil-specific constants, f and g. The two measurements, together with other soil specific constants, are then used to back calculate the water content and density in a single step. However, questions remain regarding the accuracy and bias of TDR measurements in relation to other "established" in-situ procedures such as the nuclear gage and speedy moisture. Results from an experimental program to obtain calibration constants for typical sands used in roadway construction are presented. A number of side-by-side tests are performed to compare the measurements obtained using the TDR one-step method to those obtained form other methods. Conducting such side-by-side tests is a critical step in the progress and eventual widespread usage of the one-step method. In addition, all the results are compared against an independent measurement of the in-place density from a slurry-replacement method. The objective of the independent measurement is to provide a baseline for accurate and unbiased evaluation of TDR and other technologies.

Al-Zn-Mg-Cu (7xxx series) aluminium alloys are widely used for aircraft structures. It is difficult to obtain a combination of optimal strength and stress corrosion cracking (SCC) resistance for these alloys. It appears that SCC resistance of these alloys is related to grain boundary precipitate morphology. One technique to control the grain boundary precipitate morphology is to introduce a controlled cooling procedure referred to as High Temperature Pre-precipitation (HTPP) treatment following the solution heat treatment. There is need for a detailed study of the effect of HTPP on the properties of commercial Al-Zn-Mg-Cu alloys using different intermediate temperatures. In this thesis research, the results of ten HTPP processes applied to 7075 and 7050 commercial 7xxx series alloys are presented in terms of hardness, electrical conductivity, corrosion resistance, TEM analysis of grain boundary precipitate morphology and EDS analysis of solute concentration profile at the grain boundary. Results indicate that subsequent to HTPP processing, the 7050 alloy can be precipitation aged to a higher hardness compared to 7075; this result is associated with the modification of 7050 alloy by zirconium versus chromium in 7075 alloy. HTPP heat treatment achieves better SCC resistance compared to standard T6 temper. However, it does not appear that HTPP can achieve a combination of hardness, electrical conductivity and corrosion resistance superior to standard T6 and T7X tempers. / October 2014

The effects of controlled environment strategies on the yield and quality of cherry tomato fruit production were studied between April, 2003 and September, 2004 at The University of Arizona Campus Agriculture Center; Tucson, AZ. Two cultivars of cherry tomato (Lycopersicon esculentum Mill. var. cerasiforme) planted at 2.2 plants m-2 were grown hydroponically in coconut coir and drip fertigated with a low EC (2.4 dS m-1), high EC (4.5 dS m-1), mid day relief of high EC (2.4 dS m-1 or 4.5 dS m-1 over a 24 h period) or night time super high EC treatment (12 dS m-1). From April to October, 2003, the effects of mid day relief of high EC on cherry tomato fruit yield and quality were determined. From February through September, 2004 the effects of super high EC treatment, horizontal air flow (HAF) fan operation and/or delayed fertigation on cherry tomato fruit cracking were studied.

Polymer electrolyte membrane fuel cells (PEMFCs) have the potential to play a major role as energy generators for transportation and portable applications. One of the current barriers to their commercialization is the cost of the components and manufacturing, specifically the bipolar plates. One approach to preparing PEMFCs for commercialization is to develop new bipolar plate materials, related to mass production of fuel cells. Thermoplastic/carbon filler composites with low filler loading have a major advantage in that they can be produced by a conventional low-cost injection molding technique. In addition, the materials used are inexpensive, easy to shape, and lightweight. An optimal bipolar plate must possess high surface and bulk electronic conductivity, sufficient mechanical integrity, low permeability, and corrosion resistance. However, it is difficult to achieve high electrical conductivity from a low-cost thermoplastic composite with low conductive filler loading. Concerns over electrical conductivity improvement and the injection processability of composites have brought forth the idea of producing a polypropylene/three-carbon-filler composite for bipolar plate application. The thesis addresses the development of synergistic effects of filler combinations, investigating composite conductive materials and using composite bipolar plate testing in PEMFCs. One significant effect of conductive network formation is the synergetic effects of different carbon filler sizes, shapes, and multiple filler ratios on the electrical conductivity of bipolar plate materials. A polypropylene resin combined with low-cost conductive fillers (graphite, conductive carbon black, and carbon fibers with 55 wt% of filler loading) compose the main composite for all investigations in this research. Numerous composite formulations, based on single-, two-, and three-filler systems, have been created to investigate the characteristics and synergistic effects of multiple fillers on composite conductivity. Electrical conductivity measurements corresponding to PEMFC performance and processing characteristics were investigated. Experimental work also involved other ex-situ testing for the physical requirements of commercial bipolar plates. All combinations of fillers were found to have a significant synergistic effect that increased the composite electrical conductivity. Carbon black was found to have the highest influence on the increase of electrical conductivity compared to the other fillers. The use of conjugated conducting polymers such as polypyrrole (PPy) to help the composite blends gain desirable conductivities was also studied. Electrical conductivity was significantly improved conductivity by enriching the conducting paths on the interfaces between fillers and the PP matrix with PPy. The conductive network was found to have a linkage of carbon fibers following the respective size distributions of fibers. The combination of Fortafil and Asbury carbon fiber mixture ameliorated the structure of conductive paths, especially in the through-plane direction. However, using small fibers such as carbon nanofibers did not significantly improve in electrical conductivity. The useful characteristics of an individual filler and filler supportive functions were combined to create a novel formula that significantly improved electrical conductivity. Other properties, such as mechanical and rheological ones, demonstrate the potential to use the composites in bipolar plate applications. This research contributes a direction for further improvement of marketable thermoplastic bipolar plate composite materials.

Magistriniame darbe tyrinėjamos elektroninės savybės įvairioms puslaidininkinėms medžiagoms. Tarp jų eksperimentiškai ir teoriškai tirti SbSI - tipo kristalai. Išmatuotos jų voltamperinės charakteristikos įvairiose temperatūrose bei srovės temperatūrinės priklausomybės esant skirtingai įtampai. Iš matavimų paskaičiuotas tarp metalo ir puslaidininkio susidarantis barjero aukštis, kuris vėliau buvo panaudotas teorinių – eksperimentinių rezultatų palyginimui. Eksperimentiniams elektrinio laidumo matavimams paaiškinti remtasi įvairiomis fononais stimuliuoto tuneliavimo teorijomis, kurių taikymui papildomai apskaičiuota elektronų ir fononų sąveikos konstanta esant skirtingoms temperatūroms. Taip pat įvertinti kiti, nemažiau elektriniame laidume svarbius, parametrai. Darbe parodyta, kad fononais stimulioto tuneliavimo teorijos efektyviai aprašo elektrinį laidumą tirtose medžiagose prijungiant prie jų metalo kontaktus. / In this work experimental and theoretical investigations of the high electric field electrical properties in semiconductors with Schottky barrier are presented. Experimental research is given for SbSI – type crystals. Theoretical calculations and comparison with experimental data were made using electrical phonon-assisted tunnelling model (PhAT), which is usable for explanation of temperature-field dependent conductivity in wide branch of materials: semiconductors, dielectrics, inorganic, organic and other materials. PhAT model were used including well determined parameters: effective mass of the charge carrier, participating phonon energy, barrier height and electron-phonon interaction. Barrier height was experimentally measured and found for SbSI, SbSe0.2S0.8I, SbSe0.5S0.5I, SbSeI crystals. The results of the temperature dependence of electron–phonon (e–ph) interaction in the inquiring semiconductors were also calculated. It is shown that these semiconductors have kin e–ph interaction. It varies nearly for about ~ 2.6. It has been shown that the temperature dependent I-V characteristics of SbSeI crystals can be explained by the phonon-assisted tunnelling of charge carriers from the states located in the high electric field region at the electrode-crystal junction. The electron tunnelling probability W(E, T) from traps of the apparent depth to the conduction band was computed using evaluated electron-phonon interaction constant and effective mass of the polaron. The... [to full text]

Natural geomaterials exhibit a wide range in size, physical properties, chemical properties, and mechanical behaviors. Soils that are composed of mixtures of particles with different physical and chemical properties pose a challenge to characterization and quantification of the engineering properties. This study examined the behavior of particulate mixtures composed of differently sized silica particles, mixtures composed of aluminosilicate and organic carbon particles, and mixtures composed of particles with approximately three orders of magnitude difference in particle size. This experimental investigation used elastic, electromagnetic, and thermal waves to characterize and to quantify the small to intermediate strain behavior of the mixtures. The mechanical property of stiffness of mixed materials (e.g. binary mixtures of silica particles and fly ashes with various carbon and biomass contents) was evaluated through the stiffness of active grain contacts, and the stiffness of particles which carry applied load, using the physical concepts of intergranular void ratio and interfine void ratio. Additionally, the change in both contact mode/stiffness and electrical property due to the presence of nano-sized particles (i.e., iron oxides) on the surface of soil grains was evaluated according to applied stress, packing density, iron coating density, and substrate sand particle size. Finally, the biomass fraction and total organic carbon content of mixtures was used to quantify the electrical and thermal conductivities when particulate organic was mixed with aluminosilicate particles.

Dirvožemio elektrinio laidumo (EC) matavimas yra vienas iš perspektyviausių ir dažniausiai naudojamų tiksliosios žemdirbystės tyrimų būdų. Tyrimais yra nustatyta tiesioginė jo priklausomybė su dirvožemio granuliometrine sudėtimi. Apibendrinant galima teigti, kad EC yra priemonė, leidžianti išsiaiškinti dirvožemio savybes, nuo kurių priklauso ne tik žemės ūkio, bet ir energetinių augalų, skirtų atsinaujinančios energijos gamybai, derlingumo dėsningumai. Dirvožemio elektrinis laidumas nustatytas mobiliu įrenginiu „Veris 3150 MSP“ (JAV, Veris Technogies Ltd.). Jame įrengta navigacinė sistema. Matavimai atlikti dviejuose dirvožemio pjūviuose (paviršiniame ir giluminiame): nuo dirvožemio paviršiaus iki 30 cm gylio ir 0–90 cm gylyje. Dirvožemio savybių žemėlapiai sudaryti naudojant kompiuterinę programą „SMS Advanced“ JAV, AgLeader Ltd.). Atliktų dirvožemio elektrinio laidumo tyrimų patikimumą įrodo gauta tiesinė tarpusavio priklausomybė (R2 = 0,91) tarp elektrinio laidumo nustatyto įrenginiu „Veris 3150 MSP“ ir elektrinio laidumo nustatyto laboratorijoje. Atlikus dirvožemio granuliometrinės sudėties tyrimus nustatyta, kad didėjant molio (< 2 m) ir dulkių (2–50 m) daliai dirvožemyje, jo elektrinis laidumas didėja. Labai smulkaus smėlio (50–100 m) dalelės įtakos dirvožemio elektriniam laidumui įtakos neturi, o dirvožemyje didėjant dar didesnių (> 100 m) smėlio dalelių daliai – jo elektrinis laidumas mažėja. / Soil electrical conductivity (EC) measurement is one of the most perspective and widely used research methods of precision agriculture. Various studies proved its direct correlation to soil texture. In summary, it can be stated that EC is a measure that allows defining such characteristics of soil that do influence the productivity laws not only of agricultural, but also of energy crops. Soil electrical conductivity was measured using a mobile unit Veris 3150 MSP (USA, Veris Technogies Ltd.) equipped with GPS system. Measurements were performed in two sections of soil depth (shallow and deep): from the surface up to 30 cm depth and 0–90 cm depth. Soil characteristic maps were created using computer program SMS Advanced (USA, AgLeader Ltd.). The reliability of soil electric conductivity research is proved by direct relationship (R2 = 0.91) between electrical conductivity obtained using Veris MSP and that in the laboratory. The analysis of soil texture showed that the increasing part of clay (< 2 m) and silk (2–50 m) in soil increases electrical conductivity of soil. Extremely small particles of sand (50–100 m) do not influence soil electrical conductivity, while higher amount of larger particles (> 100 m) of sand reduces its electrical conductivity.