Search results for: DC and AC conductivity

Authors: Nadine Raidl, Benjamin Kaufmann, Michael Hofstätter, Peter Supancic

Abstract:

If polycrystalline ZnO is properly doped and sintered under very specific conditions, it shows unique electrical properties, which are indispensable for today’s electronic industries, where it is used as the number one overvoltage protection material. Under a critical voltage, the polycrystalline bulk exhibits high electrical resistance but becomes suddenly up to twelve magnitudes more conductive if this voltage limit is exceeded (i.e., varistor effect). It is known that these peerless properties have their origin in the grain boundaries of the material. Electric charge is accumulated in the boundaries, causing a depletion layer in their vicinity and forming potential barriers (so-called Double Schottky Barriers, or DSB) which are responsible for the highly non-linear conductivity. Since ZnO is a piezoelectric material, mechanical stresses induce polarisation charges that modify the DSB heights and as a result the global electrical characteristics (i.e., piezotronic effect). In this work, a finite element method was used to simulate emerging stresses on individual grains in the bulk. Besides, experimental efforts were made to testify a coherent model that could explain this influence. Electron back scattering diffraction was used to identify grain orientations. With the help of wet chemical etching, grain polarization was determined. Micro lock-in infrared thermography (MLIRT) was applied to detect current paths through the material, and a micro 4-point probes method system (M4PPS) was employed to investigate current-voltage characteristics between single grains. Bulk samples were tested under uniaxial pressure. It was found that the conductivity can increase by up to three orders of magnitude with increasing stress. Through in-situ MLIRT, it could be shown that this effect is caused by the activation of additional current paths in the material. Further, compressive tests were performed on miniaturized samples with grain paths containing solely one or two grain boundaries. The tests evinced both an increase of the conductivity, as observed for the bulk, as well as a decreased conductivity. This phenomenon has been predicted theoretically and can be explained by piezotronically induced surface charges that have an impact on the DSB at the grain boundaries. Depending on grain orientation and stress direction, DSB can be raised or lowered. Also, the experiments revealed that the conductivity within one single specimen can increase and decrease, depending on the current direction. This novel finding indicates the existence of asymmetric Double Schottky Barriers, which was furthermore proved by complementary methods. MLIRT studies showed that the intensity of heat generation within individual current paths is dependent on the direction of the stimulating current. M4PPS was used to study the relationship between the I-V characteristics of single grain boundaries and grain orientation and revealed asymmetric behavior for very specific orientation configurations. A new model for the Double Schottky Barrier, taking into account the natural asymmetry and explaining the experimental results, will be given.

Keywords: Asymmetric Double Schottky Barrier, piezotronic, varistor, zinc oxide

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Authors: F. Z. Benabid, S. Kridi, F. Zouai, D. Benachour

Abstract:

The aim of present work is to characterize the PVDF/TiO2 blends as nanocomposites, and study the effect of TiO2 on properties of different compositions and the evaluation of the effectiveness of the method used for filler treatment. Nanocomposite samples were synthesized by molten route in an internal mixer. The TiO2 nanoparticles were treated with stearic acid in order to obtain a good dispersion, and the demonstration of the effectiveness of the treatment on the morphology and roughness of the nanofiller was established by microstructural analysis by FTIR and AFM. The various developed nanocomposite compositions were characterized by different methods; i.e. FTIR, XRD, SEM and optical microscopy. Rheological, dielectric and mechanical studies were also performed. The results showed a remarkable increase in the crystallinity of the PVDF/neat TiO2 nanocomposite containing 1 wt% loading of filler, due to the nucleation effect of TiO2 nanoparticles. A good dispersion was obtained in PVDF/treated TiO2 nanocomposites. The rheological study showed an increase in the fluidity in all developed nanocomposite compositions, involved by the orientation of TiO2 nanoparticles in the flow direction. The dielectric study revealed an increase in electrical conductivity in PVDF/neat TiO2 nanocomposites. However, in PVDF/ treated TiO2 nanocomposites, the electrical conductivity was decreased by the addition of 0.5 and 2 wt% loading of filler.

Keywords: nanocomposites, PVDF, TiO2, comixing, mechanical treatment

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Authors: Kwangwon Seo, Haksoo Han

Abstract:

Al-Si was synthesized and introduced in poly 2,2’-m-(phenylene)-5,5’-bibenzimidazole (PBI). As a result, a series of five Al-Si/PBI composite (ASPBI) membranes (0, 3, 6, 9, and 12 wt.%) were developed and characterized for application in high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). The chemical and morphological structure of ASPBI membranes were analyzed by Fourier transform infrared spectroscopy, X-ray diffractometer and scanning electron microscopy. According to the doping level test and thermogravimetric analysis, as the concentration of Al-Si increased, the doping level increased up to 475%. Moreover, the proton conductivity, current density at 0.6V, and maximum power density of ASPBI membranes increased up to 0.31 Scm-1, 0.320 Acm-2, and 0.370 Wcm-2, respectively, because the increased concentration of Al-Si allows the membranes to hold more PA. Alternatively, as the amount of Al-Si increased, the tensile strength of PA-doped and -undoped membranes decreased. This was resulted by both excess PA and aggregation, which can cause serious degradation of the membrane and induce cracks. Moreover, the PA-doped and -undoped ASPBI12 had the lowest tensile strength. The improved performances of ASPBI membranes imply that ASPBI membranes are possible candidates for HT-PEMFC applications. However, further studies searching to improve the compatibility between PBI matrix and inorganic and optimize the loading of Al-Si should be performed.

Keywords: composite membrane, high temperature polymer electrolyte membrane fuel cell, membrane electrode assembly, polybenzimidazole, polymer electrolyte membrane, proton conductivity

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Authors: Y. Kobayashi, T. Kurosaka, K. Yamamura, T. Yonezawa, K. Yamasaki

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The present work reports an effect of surface- modification of indium tin oxide (ITO) particles with chemicals on their electronic conductivity properties. Examined chemicals were polyvinyl alcohol (nonionic polymer), poly(diallyl dimethyl ammonium chloride) (cationic polymer), poly(sodium 4-styrene-sulfonate) (anionic polymer), (2-aminopropyl) trimethoxy silane (APMS) (silane coupling agent with amino group), and (3-mercaptopropyl) trimethoxy silane (MPS) (silane coupling agent with thiol group). For all the examined chemicals, volume resistivities of surface-modified ITO particles did not increase much when they were aged in air at 80 ^oC, compared to a volume resistivity of un-surface-modified ITO particles. Increases in volume resistivities of ITO particles surface-modified with the silane coupling agents were smaller than those with the polymers, since hydrolysis of the silane coupling agents and condensation of generated silanol and OH groups on ITO particles took place to provide efficient immobilization of them on particles. The APMS gave an increase in volume resistivity smaller than the MPS, since a larger solubility in water of APMS providing a larger amount of APMS immobilized on particles.

Keywords: indium tin oxide, particles, surface-modification, volume resistivity

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Authors: Gobinda Gopal Khan, Ashutosh K. Singh, Debasish Sarkar

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This study reports the facile fabrication of 1D ZnO/α-Fe2O3 semiconductor nano-heterostructures (SNHs), and we investigate the strong interfacial interactions at the heterojunction, resulting in novel multifunctionality in the hybrid structure. ZnO-coated α-Fe2O3 nanowires (NWs) have been prepared by combining electrodeposition and wet chemical methods. Significant improvement in electrical conductivity, photoluminescence, and room temperature magnetic properties have been observed for the ZnO/α-Fe2O3 SNHs over the pristine α-Fe2O3 NWs because of the contribution of the ZnO nanolayer. The increase in electrical conductivity in ZnO/α-Fe2O3 SNHs is because of the increase in free electrons in the conduction band of the SNHs due to the formation of type-II n-n band configuration at the heterojunction. The SNHs are found to exhibit enhanced visible green photoluminescence along with the UV emission at room temperature. The band-gap emission of the α-Fe2O3 NWs coupled to the defect emissions of the ZnO in SNHs can be attributed to the profound enhancement of the visible green luminescence. Ferromagnetism of the SNHs is found to be increased nearly five times in magnitude over the primeval α-Fe2O3 NWs, which can be ascribed to the exchange coupling of the interfacial spin at ZnO/α-Fe2O3 interface, the surface spin of ZnO nanolayer, along with the structural defects like the cation vacancies (VZn) and the singly ionized oxygen vacancies (Vo•) present in SNHs.

Keywords: nano-heterostructures, photoluminescence, electrical property, magnetism

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Authors: V. Ivanov, J. Chu, V. Stabnikov

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Different biotechnological methods for the production of construction materials and for the performance of construction processes in situ are developing within a new scientific discipline of Construction Biotechnology. The aim of this research was to develop and test new biotechnologies and biotechnological grouts for the minimization of the hydraulic conductivity of the fractured rocks and porous soil. This problem is essential to minimize flow rate of groundwater into the construction sites, the tunneling space before and after excavation, inside levies, as well as to stop water seepage from the aquaculture ponds, agricultural channels, radioactive waste or toxic chemicals storage sites, from the landfills or from the soil-polluted sites. The conventional fine or ultrafine cement grouts or chemical grouts have such restrictions as high cost, viscosity, sometime toxicity but the biogrouts, which are based on microbial or enzymatic activities and some not expensive inorganic reagents, could be more suitable in many cases because of lower cost and low or zero toxicity. Due to these advantages, development of biotechnologies for biogrouting is going exponentially. However, most popular at present biogrout, which is based on activity of urease- producing bacteria initiating crystallization of calcium carbonate from calcium salt has such disadvantages as production of toxic ammonium/ammonia and development of high pH. Therefore, the aim of our studies was development and testing of new biogrouts that are environmentally friendly and have low cost suitable for large scale geotechnical, construction, and environmental applications. New microbial biotechnologies have been studied and tested in the sand columns, fissured rock samples, in 1 m3 tank with sand, and in the pack of stone sheets that were the models of the porous soil and fractured rocks. Several biotechnological methods showed positive results: 1) biogrouting using sequential desaturation of sand by injection of denitrifying bacteria and medium following with biocementation using urease-producing bacteria, urea and calcium salt decreased hydraulic conductivity of sand to 2×10-7 ms-1 after 17 days of treatment and consumed almost three times less reagents than conventional calcium-and urea-based biogrouting; 2) biogrouting using slime-producing bacteria decreased hydraulic conductivity of sand to 1x10-6 ms-1 after 15 days of treatment; 3) biogrouting of the rocks with the width of the fissures 65×10-6 m using calcium bicarbonate solution, that was produced from CaCO3 and CO2 under 30 bars pressure, decreased hydraulic conductivity of the fissured rocks to 2×10-7 ms-1 after 5 days of treatment. These bioclogging technologies could have a lot of advantages over conventional construction materials and processes and can be used in geotechnical engineering, agriculture and aquaculture, and for the environmental protection.

Keywords: biocementation, bioclogging, biogrouting, fractured rocks, porous soil, tunneling space

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Authors: Ehsan B. Haghighi, Pavel Makhnatch, Jörgen Rogstam

Abstract:

The ice rink floor is the largest heat exchanger in an ice rink. The important part of the floor consists of concrete, and the thermophysical properties of this concrete have strong influence on the energy usage of the ice rink. The thermal conductivity of concrete can be increased by using iron ore as ballast. In this study the Transient Plane Source (TPS) method showed an increase up to 58.2% of thermal conductivity comparing the improved concrete to standard concrete. Moreover, two alternative ice rink floor designs are suggested to incorporate the improved concrete. A 2D simulation was developed to investigate the temperature distribution in the conventional and the suggested designs. The results show that the suggested designs reduce the temperature difference between the ice surface and the brine by 1-4 ˚C, when comparing with convectional designs at equal heat flux. This primarily leads to an increased coefficient of performance (COP) in the primary refrigeration cycle and secondly to a decrease in the secondary refrigerant pumping power. The suggested designs have great potential to reduce the energy usage of ice rinks. Depending on the load scenario in the ice rink, the saving potential lies in the range of 3-10% of the refrigeration system energy usage. This calculation is based on steady state conditions and the potential with improved dynamic behavior is expected to increase the potential saving.

Keywords: Concrete, iron ore, ice rink, energy saving

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Authors: Azadeh Safadoust, Ali Akbar Mahboubi

Abstract:

A study was conducted to evaluate hydraulic properties of a sandy loam soil and corn (Zea mays L.) crop production under a short-term tillage and manure combinations field experiment carried out in west of Iran. Treatments included composted cattle manure application rates [0, 30, and 60 Mg (dry weight) ha-1] and tillage systems [no-tillage (NT), chisel plowing (CP), and moldboard plowing (MP)] arranged in a split-plot design. Soil water characteristic curve (SWCC) and saturated hydraulic conductivity (Ks) were significantly affected by manure and tillage treatments. At any matric suction, the soil water content was in the order of MP>CP>NT. At all matric suctions, the amount of water retained by the soil increased as manure application rate increased (i.e. 60>30>0 Mg ha-1). Similar to the tillage effects, at high suctions the differences of water retained due to manure addition were less than that at low suctions. The change of SWCC from tillage methods and manure applications may attribute to the change of pore size and aggregate size distributions. Soil Ks was in the order of CP>MP>NT for the first two layers and in the order of MP>CP and NT for the deeper soil layer. The Ks also increased with increasing rates of manure application (i.e. 60>30>0 Mg ha-1). This was due to the increase in the total pore size and continuity.

Keywords: corn, manure, saturated hydraulic conductivity, soil water characteristic curve, tillage

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Authors: Najih Amina

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Our study focuses on monitoring the spatial evolution of a number of physico-chemical parameters of wells waters located at different distances from the discharge of the city of Khouribga (S0 upstream station, S1, S2 et S3 are respectively located at 5.5, 7.5, 11 Km away from solid waste discharge of the city). The absence of a source of drinking water in this region involves the population to feeding on its groundwater wells. Through the results, we note that most of the analyzed parameters exceed the potable water standards from S1. At this source of water, we find that the conductivity (1290 μmScm-1; Standard 1000 μmScm-1), Total Hardness TH (67.2°F/ Standard 50° F), Ca2 + (146 mg l-1 standard 60 mg l-1), Cl- (369 mg l-1 standard 150 mg l-1), NaCl (609 mgl-1), Methyl orange alakanity “M. alk” (280 mg l-1) greatly exceed the drinking water standards. By following these parameters, it is obvious that some values have decreased in the downstream stations, while others become important. We find that the conductivity is always higher than 950 μmScm-1; the TH registers 72°F in S3; Ca 2+ is in the range of 153 mg l-1 in S3, Cl- and NaCl- reached 426 mg l-1 and 702 mg l-1 respectively in S2, M alk becomes higher and reaches 430 to 350 in S3. At the wells S2, we found that the nitrites are well beyond the standard 1.05 mg l-1. Whereas, at the control station S0, the values are lower or at the limit of drinking water standards: conductivity (452 μmScm-1), TH (34 F°), Ca2+ (68 mg l-1), Cl- (157 mg l-1), NaCl- (258 mg l-1), M alk (220 mg l-1). Thus, the diagnosis reveals the presence of a high pollution caused by the leachates of the household waste discharge and by the effluents of the sewage waste water plant (SWWP). The phenomenon of the water hardness could, also, be generated by the processes of erosion, leaching and soil infiltration in the region (phosphate layers, intercalated layers of marl and limestone), phenomenons also caused by the acidity due to this surrounding pollution. The source S1 is the nearest surrounding site of the discharge and the most affected by the phenomenon of pollution, especially, it is near to a superficial water source S’1 polluted by the effluents coming from the sewage waste water plant of the city. In the light of these data, we can deduce that the consumption of this water from S1 does not conform the standards of drinking waters, and could affect the human health.

Keywords: physico-chemical parameters, ground water wells, infiltration, leaching, pollution, leachate discharge effluent SWWP, human health.

Procedia PDF Downloads 407

Authors: Seyed Hassan Nikookar, Mahmoud Fazeli-Dinan, Seyyed Payman Ziapour, Ahmad-Ali Enayati

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Background: Mosquitoes look for all kinds of aquatic habitats for laying eggs. Characteristics of water habitats are important factors in determining whether a mosquito can survive and successfully completed their developmental stages. Physicochemical factors can display an important role in vector control programs. This investigate determined whether physicochemical factors differ between habitats can be effective in the larvae density in Mazandaran province. Methods: Larvae were collected by the standard dipper up to 350 ml for 15-20 minutes from fixed habitats in 16 villages of 30 townships, the specimens identified by morphological key. Water samples were collected during larval collection and were evaluated for temperature (°C), acidity (pH), turbidity (NTU), electrical conductivity (μS/cm), alkalinity (mg/l), total hardness (mg/l), nitrate (mg/l), chloride (mg/l), phosphate (mg/l), sulfate (mg/l) in selected habitats using standard methods. Spearman Correlation coefficient was used for analyze data. Results: Totally 7566 mosquito larvae of three genera and 15 species were collected of fixed habitats. Cx. pipiens was the dominant species except in villages of Tileno, Zavat, Asad Abad, Shah Mansur Mahale which An. maculipennis, Cx. torrentium were as the predominant species. Turbidity in Karat Koti, Chloride in Al Tappeh, nitrate, phosphate and sulfate in Chalmardi, electrical conductivity, alkalinity, total hardness in Komishan villages were significantly higher than other villages (P < 0.05). There were a significant positive correlation between Cx. pipiens and Electrical conductivity, Alkalinity, Total hardness, Chloride, Cx. tritaeniorhynchus and Chloride, whereas a significant negative correlation observed between Sulfate and Cx. perexiguss. Conclusion: The correlations observed between physicochemical factor and larval density, possibly can confirm the effect of these parameters on the breeding activities of mosquitoes, and could probability facilitate larval control programs by the handwork of such factors.

Keywords: anopheles, culex, culiseta, physicochemical, habitats, larvae density, correlation

Procedia PDF Downloads 265

Authors: Thandar Zaw Win, Cho Win Aung, Gaurav Khandal, Sabyasachi Ghosh

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Systematic and comparative research on Lorenz ratios for graphene and nonrelativistic systems has been studied to identify their Wiedemann-Franz law violation domain. Fermi energy and temperature are the main governing parameters for deciding the values of the Lorenz ratio, which is basically thermal conductivity divided by electrical conductivity times temperature times Lorenz number. Metals as three-dimensional nonrelativistic electron gas are located at higher Fermi-energy by temperature domain, where Lorenz ratio remains one. Hence, they obey the Wiedemann-Franz law. By creating higher doping in a two-dimensional graphene system, one can again reach a higher Fermi-energy by temperature domain and get a constant Lorenz ratio. For both graphene and nonrelativistic systems, the Lorenz ratio goes below one if we go lower Fermi-energy by temperature domain, which is possible for the graphene system by decreasing the doping concentration. Experimentally observed greater than one Lorenz ratio in this lower Fermi-energy by temperature domain or Dirac Fluid domain indicates that nonfluid expressions of Lorenz ratio should be replaced by fluidtype expressions. We have noticed a divergent trend of Lorenz ratio in the Dirac Fluid domain using its fluid-type expression, and it matches the trend of experimental data.

Keywords: graphene, Lorentz ratio, specific heat, Wiedeann-Franz law

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Authors: Seyed Abbas Tabatabaei, Saeid Amini, Hamid Reza Ghafouri

Abstract:

One of the most important factors in flexible pavement failure is the lack of proper drainage along the roads. Water on the Paving Systems is one of the main parameters of pavement failure. Though, if water is discharged without delay and prior to discharge in order to prevent damaging the pavement the lifetime of the pavement will be considerably increased. In this study, duration of water stay and materials properties in pavement systems and the effects of aggregate gradation, and hydraulic conductivity of the drainage rate and Effects of subsurface drainage systems, drainage and reduction in the lifetime of the pavement have been studied. The study conducted in accordance with the terms offered can be concluded as under. The more hydraulic conductivity the less drainage time and the use of sub-surface drainage system causes two to three times of the pavement lifetime. In this research it has been tried by study and calculate the drained and undrained pavements lifetime by considering the effectiveness of water and drainage coefficient on flexible materials modulus and by using KENLAYER software to compare the present value cost of these pavements has been paid for a 20 year lifetime design. In this study, 14 pavement sections have been considered, of which 7 sections have been drained and 7 other not. Results show that drained pavements have more initial costs but the failure severity is so little in them and have longer lifetime for a 20 year lifetime design, the drained pavements seem so economic.

Keywords: drainage, base and sub-base, elasticity modulus, aggregation

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Authors: Priyanka Agrawal, Janou Koskamp, Amir Raoof, Mariette Wolthers

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Calcite is the main mineral found in carbonate rocks, which form significant hydrocarbon reservoirs and subsurface repositories for CO2 sequestration. The injected CO2 mixes with the reservoir fluid and disturbs the geochemical equilibrium, triggering calcite dissolution. Different combinations of fluid chemistry and injection rate may therefore result in different evolution of porosity, permeability and dissolution patterns. To model the changes in porosity and permeability Kozeny-Carman equation K∝〖(∅)〗^n is used, where K is permeability and ∅ is porosity. The value of n is mostly based on experimental data or pore network models. In pore network models, this derivation is based on accuracy of relation used for conductivity and pore volume change. In fact, at a single pore scale, this relationship is the result of the pore shape development due to dissolution. We have prepared a new reactive transport model for a single pore which simulates the complex chemical reaction of carbonic-acid induced calcite dissolution and subsequent pore-geometry evolution at a single pore scale. We use COMSOL Multiphysics package 5.3 for the simulation. COMSOL utilizes the arbitary-Lagrangian Eulerian (ALE) method for the free-moving domain boundary. We examined the effect of flow rate on the evolution of single pore shape profiles due to calcite dissolution. We used three flow rates to cover diffusion dominated and advection-dominated transport regimes. The fluid in diffusion dominated flow (Pe number 0.037 and 0.37) becomes less reactive along the pore length and thus produced non-uniform pore shapes. However, for the advection-dominated flow (Pe number 3.75), the fast velocity of the fluid keeps the fluid relatively more reactive towards the end of the pore length, thus yielding uniform pore shape. Different pore shapes in terms of inlet opening vs overall pore opening will have an impact on the relation between changing volumes and conductivity. We have related the shape of pore with the Pe number which controls the transport regimes. For every Pe number, we have derived the relation between conductivity and porosity. These relations will be used in the pore network model to get the porosity and permeability variation.

Keywords: single pore, reactive transport, calcite system, moving boundary

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Authors: Aijuka Nicholas

Abstract:

A research study was undertaken to characterize the aquifers and identify the potential groundwater recharge zones in the Kagandi district. Quantitative characterization of hydraulic conductivities of aquifers is of fundamental importance to the study of groundwater flow and contaminant transport in aquifers. A conditional approach is used to represent the spatial variability of hydraulic conductivity. Briefly, it involves using qualitative and quantitative geologic borehole-log data to generate a three-dimensional (3D) hydraulic conductivity distribution, which is then adjusted through calibration of a 3D groundwater flow model using pumping-test data and historic hydraulic data. The approach consists of several steps. The study area was divided into five sub-watersheds on the basis of artificial drainage divides. A digital terrain model (DTM) was developed using Arc GIS to determine the general drainage pattern of Kagandi watershed. Hydrologic characterization involved the determination of the various hydraulic properties of the aquifers. Potential groundwater recharge zones were identified by integrating various thematic maps pertaining to the digital elevation model, land use, and drainage pattern in Arc GIS and Sufer golden software. The study demonstrates the potential of GIS in delineating groundwater recharge zones and that the developed methodology will be applicable to other watersheds in Uganda.

Keywords: aquifers, Arc GIS, groundwater recharge, recharge zones

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Authors: A. S. Hakeem, B. Ahmed, M. Ehsan, A. Ibrahim, H. M. Irshad, T. Laoui

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Alumina (Al2O3) - cubic boron nitride (cBN) ceramic composites were sintered by spark plasma sintering (SPS) using α-Al2O3 particle sizes; 150 µm, 150 nm and cBN particle size of 42 µm. Alumina-cBN composites containing 10, 20 and 30wt% cBN with and without Ni coated were sintering at an elevated temperature of 1400°C at a constant uniaxial pressure of 50 MPa. The effect of matrix particle size, cBN and Ni content on mechanical properties and thermal properties, i.e., thermal conductivity, diffusivity, expansion, densification, phase transformation, microstructure, hardness and toughness of the Al2O3-cBN/(Ni) composites under specific sintering conditions were investigated. The highest relative densification of 150 nm-Al2O3 containing 30wt% cBN (Ni coated) composite was 99% at TSPS = 1400°C. In case of 150 µm- Al2O3 compositions, the phase transformation of cBN to hBN were observed, and the relative densification decreased. Thermal conductivity depicts maximum value in case of 150 nm- Al2O3-30wt% cBN-Ni composition. The Vickers hardness of this composition at TSPS = 1400°C also showed the highest value of 29 GPa.

Keywords: alumina composite, cubic boron nitride, mechanical properties, phase transformation, Spark plasma sintering

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Authors: Shahin Farajifar, Azadeh Safadoust, Ali Akbar Mahboubi

Abstract:

A study was conducted to evaluate hydraulic properties of a sandy loam soil and corn (Zea mays L.) crop production under a short-term tillage and manure combinations field experiment carried out in west of Iran. Treatments included composted cattle manure application rates [0, 30, and 60 Mg (dry weight) ha-1] and tillage systems [no-tillage (NT), chisel plowing (CP), and moldboard plowing (MP)] arranged in a split-plot design. Soil water characteristic curve (SWCC) and saturated hydraulic conductivity (Ks) were significantly affected by manure and tillage treatments. At any matric suction, the soil water content was in the order of MP>CP>NT. At all matric suctions, the amount of water retained by the soil increased as manure application rate increased (i.e. 60>30>0 Mg ha-1). Similar to the tillage effects, at high suctions the differences of water retained due to manure addition were less than that at low suctions. The change of SWCC from tillage methods and manure applications may attribute to the change of pore size and aggregate size distributions. Soil Ks was in the order of CP>MP>NT for the first two layers and in the order of MP>CP and NT for the deeper soil layer. The Ks also increased with increasing rates of manure application (i.e. 60>30>0 Mg ha-1). This was due to the increase in the total pore size and continuity.

Keywords: corn, manuure, saturated hydraulic conductivity, soil water characteristic curve, tillage

Procedia PDF Downloads 74

Authors: Manisha A. Hira, Arup Rakshit

Abstract:

Textile substrates are endowed with flexibility and ease of making–up, but are non-conductors of electricity. Conductive materials like carbon can be incorporated into textile structures to make flexible conductive materials. Such conductive textiles find applications as electrostatic discharge materials, electromagnetic shielding materials and flexible materials to carry current or signals. This work focuses on use of carbon fiber as conductor of electricity. Carbon fibers in staple or tow form can be incorporated in textile yarn structure to conduct electricity. The paper highlights the process for development of these conductive yarns of polyester/carbon using Friction spinning (DREF) as well as ring spinning. The optimized process parameters for processing hybrid structure of polyester with carbon tow on DREF spinning and polyester with carbon staple fiber using ring spinning have been presented. The studies have been linked to highlight the electrical conductivity of the developed yarns. Further, the developed yarns have been incorporated as weft in fabric and their electrical conductivity has been evaluated. The paper demonstrates the structure and properties of fabrics developed from such polyester/carbon blend yarns and their suitability as electrically dissipative fabrics.

Keywords: carbon fiber, conductive textiles, electrostatic dissipative materials, hybrid yarns

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Authors: Fayssal Ynineb, Toufik Hadjersi, Fatsah Moulai, Wafa Achour

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Currently, tremendous attention has been paid to the rational design and synthesis of core/shell heterostructures for high-performance supercapacitors. In this study, the hierarchical NiO/ZnCo₂O₄ Core-Shell Nanorods Arrays were successfully deposited onto ITO substrate via a two-step hydrothermal and electrodeposition methods. The effect of the thin carbon layer between NiO and ZnCo₂O₄ in this multi-scale hierarchical structure was investigated. The selection of this structure was based on: (i) a high specific area of pseudo-capacitive NiO to maximize specific capacitance; (ii) an effective NiO-electrolyte interface to facilitate fast charging/discharging; and (iii) conducting carbon layer between ZnCo₂O₄ and NiO enhance the electric conductivity which reduces energy loss, and the corrosion protection of ZnCo₂O₄ in alkaline electrolyte. The obtained results indicate that hierarchical NiO/ZnCo₂O₄ present a high specific capacitance of 63 mF.cm⁻² at a current density of 0.05 mA.cm⁻² higher than that of pristine NiO and ZnCo₂O₄ of 6 and 3 mF.cm⁻², respectively. The carbon layer improves the electrical conductivity among NiO and ZnCo₂O₄ in the hierarchical NiO/C/ZnCo₂O₄ electrode. As well, the specific capacitance drastically increased to reach 125 mF.cm⁻². Moreover, this multi-scale hierarchical structure exhibits superior cycling stability with ~ 95.7 % capacitance retention after 65k cycles. These results indicate that the NiO/C/ZnCo₂O₄ nanocomposite material is an outstanding electrode material for supercapacitors.

Keywords: NiO/C/ZnCo₂O₄, specific capacitance, hydrothermal, supercapacitors

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Authors: G. Nyongombe, Guy L. Kabongo, B. M. Mothudi, M. S. Dhlamini

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A series of Transition Metals Oxides (TMOs) doped graphene were synthesized and successfully used as supercapacitor electrode materials. The as-synthesized materials exhibited exceptional electrochemical properties owing to the combined properties of its constituents; high surface area and good conductivity were achieved. Several analytical characterization techniques were employed to investigate the morphology, crystal structure atomic arrangement and elemental chemical state in the materials for which scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were conducted, respectively. Moreover, the electrochemical properties of the as-synthesized materials were examined by performing cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) measurements. Furthermore, the effect of doping concentration on the interlayer distance of the graphene materials and the charge transfer resistance are investigated and correlated to the exceptional current density which was multiplied by a factor of ~80 after TMOs doping in graphene. Finally, the resulting high capacitance obtained confirms the contribution of grapheme exceptional electronic conductivity and large surface area on the electrode materials. Such good-performing electrode materials are highly promising for supercapacitors and other energy storage devices.

Keywords: energy density, graphene, supercapacitors, TMOs

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Authors: M. E. Silva, I. Brás

Abstract:

To study the influence of different organic amendments on the quality of poultry manure compost, three pilot composting trials were carried out with different mixes: poultry manure/carcasse meal/ashes/grape pomace (Pile 1), poultry manure/ cellulosic sludge (Pile 2) and poultry manure (Pile 3). For all piles, wood chips were applied as bulking agent. The process was monitored, over time, by evaluating standard physical and chemical parameters, such as, pH, electric conductivity, moisture, organic matter and ash content, total carbon and total nitrogen content, carbon/nitrogen ratio (C/N) and content in mineral elements. Piles 1 and 2 reached a thermophilic phase, however having different trends. Pile 1 reached this phase earlier than Pile 2. For both, the pH showed a slight alkaline character and the electric conductivity was lower than 2 mS/cm. Also, the initial C/N value was 22 and reached values lower than 15 at the end of composting process. The total N content of the Pile 1 increased slightly during composting, in contrast with the others piles. At the end of composting process, the phosphorus content ranged between 54 and 236 mg/kg dry matter, for Pile 2 and 3, respectively. Generally, the Piles 1 and 3 exhibited similar heavy metals content. This study showed that organic amendments can be used as carbon source, given that the final composts presented parameters within the range of those recommended in the 2^nd Draft of EU regulation proposal (DG Env.A.2 2001) for compost quality.

Keywords: co-composting, compost quality, organic ammendment, poultry manure

Procedia PDF Downloads 305

Authors: Nilufar Chowdhury, Fereydoun Najafian Jazi, Omid Ghasemi-Fare

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The thermal effect on soil properties induces significant variations in hydraulic conductivity, which is attributable to temperature-dependent transitions in soil properties. With the elevation of temperature, there can be a notable increase in intrinsic permeability due to the degeneration of bound water molecules into a free state facilitated by thermal energy input. Conversely, thermal consolidation may cause a reduction in intrinsic permeability as soil particles undergo densification. This thermal response of soil permeability exhibits pronounced heterogeneity across different soil types. Furthermore, this temperature-induced disruption of the bound water within clay matrices can enhance the mineral-to-mineral contact, initiating irreversible deformation within the clay structure. This indicates that when soil undergoes heating-cooling cycles, plastic strain can develop, which needs to be investigated for every soil type to understand the thermo-hydro mechanical behavior of clay properly. This research aims to study the effect of the heating-cooling cycle on the intrinsic permeability and time-dependent evaluation of thermal volume change of sodium Bentonite clay. A temperature-controlled triaxial permeameter cell is used in this study. The selected temperature is 20° C, 40° C, 40° C and 80° C. The hydraulic conductivity of Bentonite clay under 100 kPa confining stresses was measured. Hydraulic conductivity analysis was performed on a saturated sample for a void ratio e = 0.9, corresponding to a dry density of 1.2 Mg/m3. Different hydraulic gradients were applied between the top and bottom of the sample to obtain a measurable flow through the sample. The hydraulic gradient used for the experiment was 4000. The diameter and thickness of the sample are 101. 6 mm, and 25.4 mm, respectively. Both for heating and cooling, the hydraulic conductivity at each temperature is measured after the flow reaches the steady state condition to make sure the volume change due to thermal loading is stabilized. Thus, soil specimens were kept at a constant temperature during both the heating and cooling phases for at least 10-18 days to facilitate the equilibration of hydraulic transients. To assess the influence of temperature-induced volume changes of Bentonite clay, the evaluation of void ratio change during this time period has been monitored. It is observed that the intrinsic permeability increases by 30-40% during the heating cycle. The permeability during the cooling cycle is 10-12% lower compared to the permeability observed during the heating cycle at a particular temperature. This reduction in permeability implies a change in soil fabric due to the thermal effect. An initial increase followed by a rapid decrease in void ratio was observed, representing the occurrence of possible osmotic swelling phenomena followed by thermal consolidation. It has been observed that after a complete heating-cooling cycle, there is a significant change in the void ratio compared to the initial void ratio of the sample. The results obtained suggest that Bentonite clay’s microstructure can change subject to a complete heating-cooling process, which regulates macro behavior such as the permeability of Bentonite clay.

Keywords: bentonite, permeability, temperature, thermal volume change

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Authors: Azadeh Safadoust, Ali Akbar Mahboubi, Mohammad Reza Mosaddeghi, Bahram Gharabaghi

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A study was conducted to evaluate hydraulic properties of a sandy loam soil and corn (Zea mays L.) crop production under a short-term tillage and manure combinations field experiment carried out in west of Iran. Treatments included composted cattle manure application rates [0, 30, and 60 Mg (dry weight) ha⁻¹] and tillage systems [no-tillage (NT), chisel plowing (CP), and moldboard plowing (MP)] arranged in a split-plot design. Soil water characteristic curve (SWCC) and saturated hydraulic conductivity (Ks) were significantly affected by manure and tillage treatments. At any matric suction, the soil water content was in the order of MP>CP>NT. At all matric suctions, the amount of water retained by the soil increased as manure application rate increased (i.e. 60>30>0 Mg ha⁻¹). Similar to the tillage effects, at high suctions the differences of water retained due to manure addition were less than that at low suctions. The change of SWCC from tillage methods and manure applications may attribute to the change of pore size and aggregate size distributions. Soil Ks was in the order of CP>MP>NT for the first two layers and in the order of MP>CP and NT for the deeper soil layer. The Ks also increased with increasing rates of manure application (i.e. 60>30>0 Mg ha⁻¹). This was due to the increase in the total pore size and continuity.

Keywords: corn, manure, saturated hydraulic conductivity, soil water characteristic curve, tillage

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Authors: Vladimir Mantsevich, Natalya Maslova, Petr Arseyev

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We investigated the tunneling current peculiarities in the system of two coupled by means of the external field quantum dots (QDs) weakly connected to the electrodes in the presence of Coulomb correlations between localized electrons by means of Heisenberg equations for pseudo operators with constraint. Special role of multi-electronic states was demonstrated. Various single-electron levels location relative to the sample Fermi level and to the applied bias value in symmetric tunneling contact were investigated. Rabi frequency tuning results in the single-electron energy levels spacing. We revealed the appearance of negative tunneling conductivity and demonstrated multiple switching "on" and "off" of the tunneling current depending on the Coulomb correlations value, Rabi frequency amplitude and energy levels spacing. We proved that Coulomb correlations strongly influence the system behavior. We demonstrated the presence of multi-stability in the coupled QDs with Coulomb correlations when single value of the tunneling current amplitude corresponds to the two values of Rabi frequency in the case when both single-electron energy levels are located slightly above eV and are close to each other. This effect disappears when the single-electron energy levels spacing increases.

Keywords: Coulomb correlations, negative tunneling conductivity, quantum dots, rabi frequency

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Authors: A. O. David, A. A. Akaho, M. A. Abah, J. O. Ogunjimi

Abstract:

This study focuses on the growing concerns about the quality of groundwater found around cement factories, which have caused several health issues for residents located within two (2) kilometer radius. The qualities of groundwater were determined by an investigative study that involved the determination of some heavy metals and physicochemical properties in drinking water samples. Eight (8) samples of groundwater were collected from the eight sampling sites. The samples were analysed for the following parameters; iron, copper, manganese, zinc, lead, color, dissolved solids, electrical conductivity, pH, dissolved oxygen (DO), biological oxygen demand (BOD), chemical oxygen demand (COD), temperature, turbidity and total hardness using standard methods. The test results showed the variation of the investigated parameters in the samples as follows: temperature 26-31oC, pH 5.9-7.2, electrical conductivity (EC) 0.37 – 0.78 µS/cm, total hardness 181.8 – 333.0 mg/l, turbidity 0.00-0.05 FTU, colour 5-10 TCU, dissolved oxygen 4.31-5.01 mg/l, BOD 0.2-1.0 mg/l, COD 2.0 -4.0 mg/l, Cu 0.04 – 0.09 mg/l, Fe 0.006-0.122 mg/l, Zn 0.016-0.306 mg/l, Mn 0.01-0.05 mg/l and Pb < 0.001 mg/l. The World Health Organization's standard for drinking water quality guidelines was exceeded in several of the analyzed parameters' amounts in the drinking water samples from the study area. The dissolved oxygen was found to exceed 5.0 mg/l, which is the WHO permissible limit; also, Limestone was found to exceed the WHO maximum limit of 170 mg/l. All the above results confirmed the high pollution of the groundwater sources, and hence, they are not suitable for consumption without any prior treatment.

Keywords: groundwater, quality, heavy metals, parameters

Procedia PDF Downloads 64

Authors: Hayder H. Kareem, Ayad K. Hussein, Aseel A. Alkatib

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Groundwater accumulated at geological formations constitutes a worldwide vital water resource component which can be used to supply agriculture, industry, and domestic uses. The subsurface environment is affected by human activities; consequently, planning and sustainable management of aquifers require serious attention, especially as the world is exposed to the problem of global warming. Establishing accurate and efficient groundwater models will provide confident results for the behavior of the aquifer's system. The new approach, 'Distributed Value Property Zones,' available in Visual MODFLOW, is used to reconstruct the subsurface zones of the Al-Najaf region aquifer, and then its effect is compared with those manual and automated (PEST) approaches. Results show that the model has become more accurate with the use of the new approach, as the calibration and results analyses revealed. The assessment of the Al-Najaf region groundwater aquifer has revealed a degree of insufficiency of the required pumping demand, which reflects dry areas in both of the aquifer's layers. In addition, with pumping, the Euphrates River loses water of 7458 m³/day to the aquifer, while without pumping, it gains 28837 m³/day from the rainfall's recharge. The distributed value property zones approach achieves a precise groundwater model to assess the state of the Al-Najaf region aquifer.

Keywords: Al-Najaf region, distributed value property zones approach, hydraulic conductivity, groundwater modelling using visual MODFLOW

Procedia PDF Downloads 171

Authors: Syed A. Bukhari, Ankur Goswmai, Dale Hume, Thomas Thundat

Abstract:

Here we demonstrate mechanical detection of photo-induced Insulator to metal transition (MIT) in ultra-thin vanadium dioxide (VO₂) micro strings by using < 100 µW of optical power. Highly focused laser beam heated the string locally resulting in through plane and along axial heat diffusion. Localized temperature increase can cause temperature rise > 60 ºC. The heated region of VO₂ can transform from insulating (monoclinic) to conducting (rutile) phase leading to lattice compressions and stiffness increase in the resonator. The mechanical frequency of the resonator can be tuned by changing optical power and wavelength. The first mode resonance frequency was tuned in three different ways. A decrease in frequency below a critical optical power, a large increase between 50-120 µW followed by a large decrease in frequency for optical powers greater than 120 µW. The dynamic mechanical response was studied as a function of incident optical power and gas pressure. The resonance frequency and amplitude of vibration were found to be decreased with increasing laser power from 25-38 µW and increased by1-2 % when the laser power was further increased to 52 µW. The transition in films was induced and detected by a single pump and probe source and by employing external optical sources of different wavelengths. This trend in dynamic parameters of the strings can be co-related with reversible Insulator to metal transition in VO₂ films which creates change in density of the material and hence the overall stiffness of the strings leading to changes in string dynamics. The increase in frequency at a particular optical power manifests a transition to a more ordered metallic phase which tensile stress onto the string. The decrease in frequency at higher optical powers can be correlated with poor phonon thermal conductivity of VO₂ in conducting phase. Poor thermal conductivity of VO₂ can force in-plane penetration of heat causing the underneath SiN supporting VO₂ which can result as a decrease in resonance frequency. This noninvasive, non-contact laser-based excitation and detection of Insulator to metal transition using micro strings resonators at room temperature and with laser power in few µWs is important for low power electronics, and optical switching applications.

Keywords: thermal conductivity, vanadium dioxide, MEMS, frequency tuning

Procedia PDF Downloads 120

Authors: F.I. Adeosun, A.A. Idowu, D.O. Odulate,

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The aims of carrying out this experiment were to determine the water quality and to investigate if the various human and ecological activities around the river have any effect on the physico-chemical parameters of the river’s resources with a view to effectively utilizing these resources. Water samples were collected from two stations on the surface water of Lower Ogun River Akomoje biweekly for a period of 5 months (January to May, 2011). Results showed that temperature ranged between 24.0-30.7oC, transparency (0.53-1.00 m), depth (1.0-3.88 m), alkalinity (4.5-14.5 mg/l), nitrates (0.235-5.445 mg/l), electrical conductivity (140-190µS/cm), dissolved oxygen (4.12-5.32 mg/l), phosphates (0.02 mg/l-0.7 5 mg/l) and total dissolved solids (70-95).The parameters at the deep end (station A) accounted for the bulk of the highest values; there was however no significant differences between the stations at P˂0.05 with the exception of transparency, depth, total dissolved solids and electrical conductivity. The phosphate value was relatively low which accounted for the low productivity and high transparency. The results obtained from the physico-chemical parameters agreed with the limits set by both national and international bodies for drinking and fish growth. It was however observed that during the period of data collection, catch was low and this could be attributed to low level of primary productivity due to the quality of physico-chemical parameters of the water. It is recommended that the agencies involved in the management of the river should put the right policies in place that will effectively enhance proper exploitation of the water resources. More research should also be carried out on the physico-chemical parameters since this work only studied the water for five months.

Keywords: physical, chemical, parameters, water quality, Ogunriver

Procedia PDF Downloads 681

Authors: Onifade Yemi Sikiru, Vwoke Eruya

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An investigation has been made of the groundwater potentials of Erusu-Arigidi, Ondo State, Nigeria and using an electrical resistivity survey. This study was motivated to determine the electrical resistivity parameters of the area. This work aims to use the electrical resistivity method to explore the groundwater potentials of the study area. A total of ten vertical electrical soundings (VES) were conducted with a maximum electrode spacing of 150 m. The data was acquired using ABEM SAS 1000 Terrameter and processed using WINRESIST. The interpreted and analyzed results reveal four to six geoelectric layers. The VES curves obtained were QH, H, AAA, HKH, and HA. Findings from the study revealed that the geoelectric layer ranges from 3 to 5 layers. From the result, the Dar Zarrouk parameters longitudinal conductance (S) and transverse resistance (Tr), average longitudinal resistance (), transverse resistivity (), coefficient of anisotropy (λ), and reflection coefficient ranges from 0.22 to 1.45mhos, 67.12 to 4262.91 Ω/m², 8.81 to 76.12 Ω-m, 12.0 to 243.5 Ωm², 1.01 to 1.78, and 0.72 to 0.99 respectively. Deduction from S suggested that groundwater tends to be slightly vulnerable to surface contamination. Further findings from Dar Zarrouk parameters revealed that southwest parts of the study area tend to have high groundwater potential when compared to other parts of the study area. While hydraulic conductivity and transmissivity range from 0.003 to 0.051m/day, and 11.16 to 158.30m²/day, results obtained from H and T revealed northwest parts of the study area are considered to be aquiferous when compared to other parts of the research area.

Keywords: variation, isoresistivity, hydraulic conductivity, groundwater

Procedia PDF Downloads 77

Authors: Hamad Almohamadi, Nabeel Alharthi, Majed Alamoudi

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Biphasic electrodes featuring CuSx/NiSx electrodeposited on nickel foam have been investigated for their electrocatalytic activity in water splitting. The study investigates the impacts of an S-vacancy induced biphasic design on the overpotential and Tafel slope. According to the findings, the NiSx/CuSx/NF electrode with S-vacancy defects displays stronger oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activity with lower overpotential and a steeper Tafel slope than the non-defect sample. NiSx/CuSx/NF exhibits the lowest overpotential value of 212 mV vs reversible hydrogen electrode (RHE) for OER and −109 mV vs RHE for HER at 10 mA cm−2. Tafel slope of 25.4 mV dec−1 for OER and −108 mV dec−1 for OER found of that electrode. The electrochemical surface area (ECSA) and diffusion impedance of the electrode is calculated. The maximum ECSA, lowest series resistance and lowest charge transfer resistance are found in the *NiSx/CuSx/NF sample with S-vacancy defects, showing increased electrical conductivity and quick charge transfer kinetics. The *NiSx/CuSx/NF electrode was found to be stable for 80 hours in pure water splitting and 20 hours in sea-water splitting. The investigation comes to the conclusion that the enhanced water splitting activity and electrical conductivity of the electrode are caused by S-vacancy defects resulting in improved water splitting performance.

Keywords: water splitting, electrocatalyst, biphasic design, electrodeposition

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Authors: Sinwook Park, Gilad Yossifon

Abstract:

The presence of a floating electrode array located within the depletion layer formed due to concentration-polarization (CP) across a microchannel-membrane device, produces not only induced-charge electro-osmosis (ICEO) vortex and but also a bipolar current resulting from faradaic reactions. It has been shown that there exists an optimal SiO2 layer thickness of ~50nm which is sufficient to suppress bipolar currents (at least up to 5V applied voltage) but still enables ICEO vortices that stir the depletion layer, thereby affecting its I-V response. This effect is pronounced beyond the limiting current where the existence of the depletion layer results in increased local electric field due to decreased solution conductivity. This comprehensive study of the interaction of embedded electrodes with the induced CP in microchannel-perm selective medium systems, allows one to choose the thickness of the thin dielectric coating to either enhance the mixing as a means to control the diffuse layer, or suppress it, for example, in the case where electrodes are intended for local measurements of the solution conductivity with minimal invasion. In addition, the use of alternating-current electro-osmosis by activating electrodes results in further enhancement of the fluid stirring and opens new routes for on-demand spatiotemporal control of the CP length. In addition, the use of embedded heaters within the depletion layer generates electro-thermal vortices that in turn also control the CP length.

Keywords: AC electrokinetics, microchannel, concentration-polarization, bipolar current

Procedia PDF Downloads 497