A firm knowledge about the interaction between the metal surface and adsorbed molecules is imperative for formulating procedures to synthesize nanoparticles (NPs) with predetermined shape and size. The ligand‐metal interaction during NP formation can be mimicked on an electrode surface by electrosorbing ligand molecules on a charged metal surface. Electrochemical methods can provide an ideal platform to study the adsorption behaviour of molecules at the solid‐liquid interface. In addition to classical electrochemical techniques, the combination of spectroscopy with electrochemical methods amplifies mechanistic insights about the surface adsorption processes. The adsorption behaviour of pyridine and one of its derivatives, 4‐dimethylamino pyridine (DMAP) have been well studied due to their potential application in nanoparticle synthesis. However, prior to this work, there has been very limited and conflicting literature available about the adsorption of of pyridine derivatives analogous to DMAP. Among the pyridine derivatives that were studied, some reports indicate that, other than DMAP, only 4‐methoxy pyridine (MOP) can stabilize gold nanoparticles. However, very little is known about the possible differences in the adsorption energy and general behaviour of MOP compared to DMAP. Resolving this knowledge gap is imperative to resolving the conflicting information about pyridine‐based stabilizers for metal nanoparticle applications. The adsorption behaviour of MOP on different crystallographic Au surfaces as a function of pH and surface potential has been investigated in this project. These studied were carried out using classical electrochemical methods including chronocoulometry and differential capacity, as well as modern spectroscopic techniques like Surface Enhanced Infrared Absorption Spectroscopy (SEIRAS). The thermodynamic parameters obtained from electrochemical data shows that adsorption features of MOP is similar to that of DMAP. However, there is a significant difference in the adsorption strength of MOP and DMAP at positive potentials. The SEIRAS data provides much more detailed information about the potential depended orientation of MOP on polycrystalline Au. Cumulative analysis of electrochemical and spectroscopic data provides strong evidence that MOP can stabilize Au(111) facets over wide pH ranges. Moreover, this work provides convincing evidence that the basic nature of substituted pyridine alters the metal to ligand adsorption strength.

Thesis (PhD)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: This dissertation considers the wideband modelling of capacitive voltage sensors for open-air transmission line applications. Two novel topologies were introduced, namely a differential parallel plate sensor with a floating faraday cage for the interface instrumentation and a coaxial sensor mounted around the earth conductor with a faraday cage connected to the earth conductor. The modelling and analysis procedures included the derivation of equivalent circuit models in order to simulate the calibration factor, the loading effect of the interface instrumentation and the effect of leakage to ground, both in the time- and frequency domain. In order to obtain a flat frequency response from very low frequencies (less than 5 Hz) to very high frequencies (several MHz) it is important that the interface instrumentation have a high input impedance and galvanic isolation be maintained. This was achieved by developing interface instrumentation with a fibre-optic link operated from battery power. The instrumentation represents a fairly unique approach in that the data is digitised before transmission across the serial fibre-optical link, where-as conventional interfaces use analogue optical technology. Despite the added complexity and high power requirements introduced by the digitising process, the improved versatility is expected to yield a superior interface solution. The instrumentation has a bandwidth of approximately 6 MHz, with an optional anti-aliasing filter at 1 MHz. Special consideration should be given to the support structure as any unbalanced leakage to ground will introduce variations in the frequency response towards the low-frequency end. Leakage of a 100 MQ was found to influence the frequency response of the circuit up to frequencies of 1 kHz. Extensive simulation studies were conducted to obtain qualitative and quantitative insight into the differential sensor topology and the associated electric fields. The improvement of a differential plate sensor over the traditional single element plate sensor was demonstrated using twodimensional simulations. Further simulations with a three-dimensional package showed that the two-dimensional simulations are insufficient, because the boundary conditions and end effects have a great influence on the calibration factor of the sensor. Extensive laboratory tests were also undertaken to evaluate the sensor topology as well as the effects of the interface instrumentation and leakage to ground. Excellent correlation were found between the measured and simulated waveforms, both in the time- and frequency domains regarding the calibration factor as well as the added poles or zeros at low frequencies. It can therefore be deduced that a valid circuit model was suggested for these sensor topologies in the frequency range from 10 Hz to 1 MHz. Keywords: Capacitive sensors, Open-air voltage sensors / AFRIKAANSE OPSOMMING: Hierdie verhandeling beskou die wyeband modellering van kapasitiewe spanningsensors vir opelug transmissie lyn toepassings. Twee oorspronklike topologieë is voorgestel, naamlik 'n differensiële parallel plaat sensor met 'n aparte faraday hok vir die koppelvlak instrumentasie en 'n koaksiale sensor wat rondom die aardgeleier monteer word met die faraday hok ook aan die aardgeleier gekoppel. Die modellerings en analise prosedures het ingesluit die afleiding van ekwivalente stroombaanmodelle vir simulasie van die kalibrasiefaktor asook die belasingseffek van die koppelvlak instrumentasie en lekweerstand na grond in beide die tyd- en frekwensie gebiede. Om 'n plat frekwensieweergawe te verkry vanaf baie lae frekwensies (laer as 5 Hz) tot by baie hoë frekwensies Cn paar MHz), is dit belangrik dat die koppelvlak instrumentasie 'n hoë intreeimpedansie het en galvaniese isolasie verseker word. Dit was bereik deur koppelvlak instrumentasie te ontwikkel met 'n optiese vesel koppeling wat met battery krag aangedryf word. Die instrumentasie verskaf 'n redelik unieke aanslag in die opsig dat die data gemonster word voordat dit oor die seriële optiese vesel skakel gestuur word, terwyl konvensionele koppelvlakke analoog optiese tegnologie gebruik. Ten spyte van die toegevoegde kompleksiteit en hoë drywingsvereistes van die versyferingsproses, het die instrumentasie se veelsydigheid toegeneem tot die mate dat dit as 'n beter koppelvlak oplossing beskou word. Die instrumentasie het 'n bandwydte van ongeveer 6 MHz, met 'n opsionele teen-vou filter by 1 MHz. Die ondersteuningstruktuur is van besondere belang aangesien enige ongebalanseerde lekweerstand na grond afwykings in die frekwensieweergawe sal veroorsaak aan die lae frekwensie kant. Lekweerstand van 100 MQ sal die frekwensieweergawe beïvloed tot by ongeveer 1 kHz. Uitgebreide simulasies is gedoen om kwalitatiewe en kwantitatiewe insig in die differensiële sensor topologie en die geassosieerde elektriese velde te verkry. Die verbetering van 'n differensiële parallel plaat sensor in vergelyking met die tradisionele enkel element plaat sensor is demonstreer met twee-dimensionele simulasies. Verdere simulasies met 'n drie-dimensionele pakket het gewys dat die twee- dimensionele simulasies onvoldoende is aangesien grensvoorwaardes en randeffekte 'n groot invloed het op die kalibrasiefaktor van die sensor. Uitgebreide laboratorium toetse is ook gedoen om die sensor topologie sowel as die effekte van die koppelvlak instrumentasie en lekweerstand na grond te evalueer. Uitstekende korrelasie is gevind tussen gemete en voorspelde golfvorms, in beide die tyd- en frekwensie gebied met betrekking tot die kalibrasie faktor sowel as die toegevoegde pole en zeros by lae frekwensies. Die gevolgtrekking is dus dat 'n geldige stroombaanmodel voorgestel is vir die sensor topologieë vir die frekwensie bereik van 10Hz to 1 MHz. Sleutelwoorde: Kapasitiewe sensors, Ope-lug spanningsensors

Switched reluctance motor (SRM) has become a competitive selection for many applications of electric machine drive systems recently due to its relative simple construction and its robustness. The advantages of those motors are high reliability, easy maintenance and good performance. The absence of permanent magnets and windings in rotor gives possibility to achieve very high speeds (over 10000 rpm) and turned SRM into perfect solution for operation in hard conditions like presence of vibrations or impacts. Such simple mechanical structure greatly reduces its price. Due to these features, SRM drives are used more and more into aerospace, automotive and home applications. The major drawbacks of the SRM are the complicated algorithm to control it due to the high degree of nonlinearity, also the SRM has always to be electronically commutated and the need of a shaft position sensor to detect the shaft position, the other limitations are strong torque ripple and acoustic noise effects.

abstract: ABSTRACT Programmable metallization cell (PMC) technology uses the mechanism of metal ion transport in solid electrolytes and electrochemical redox reactions to form metallic electrodeposits. When a positive bias is applied from anode to cathode, atoms at the anode are oxidized to ions and dissolve in the solid electrolyte. They travel to the cathode under the influence of an electric field, where they are reduced to form electrodeposits. These electrodeposits are filamentary in nature and grow in different patterns. Devices that make use of the principle of filament growth have applications in memory, RF switching, and hardware security. The solid electrolyte under investigation is tungsten trioxide with copper deposited on top. For a standard PMC, these layers are heated in a convection oven to dope the electrolyte. Once the heating process is completed, electrodes are deposited on top of the electrolyte and biased to grow the filaments. What is investigated is the rate of dendritic growth to applied field on the PMC and the composition of the electrolyte. Also investigated are modified three-terminal PMC capacitance change devices. These devices have a buried sensing electrode that senses the increasing capacitance as the filaments grow and increase the upper electrode area. The rate of dendritic growth in the tungsten trioxide and copper electrolyte of different chemistries and applied field to the PMC devices is the important parameter. The rate of dendritic growth is related to the change of capacitance. Through sensing the change in capacitance over time the modified PMC device will function as an odometer device that can be attached to chips. The attachment of these devices to chips, help in preventing illegal recycling of old chips by marking those chips as old. This will prevent would-be attackers from inserting modified chips in systems that will enable them to by-pass any software security precautions. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2019

The electrochemical double layer (EDL) at the solid–liquid interface is the near surface region where important electrochemical processes (e.g., electrodeposition, corrosion, and heterogeneous catalysis) take place. Subtle changes in the electrode surface material/topography and the nature of the fluid medium can drastically alter interactions between liquid molecules and the solid surface. A better understanding of this interfacial region can help advance numerous applied fields, such as battery technologies, solar cells, double layer capacitors, and carbon dioxide capture/conversion. Ionic liquids (IL) are an emerging class of solvents that could replace traditional aqueous/non-aqueous solvents due to their advantageous physiochemical properties (e.g., wide solvent window, high thermal stability, and excellent solvating power). However, our understanding of the near-surface structure of ILs in the EDL is still being developed. This thesis focuses on the fundamental electrochemical behavior of ILs to help understand its interfacial behavior in three main areas: 1) the nature of capacitance-potential relationships in neat ILs, 2) the role of ‘user-defined’ experimental variables on capacitive electrochemical measurements, and 3) the impact of IL + water mixtures on experimental data. The general shape of capacitance-potential curves can suggest at the broad architecture of the EDL region. Fundamental capacitive studies of the IL EDL show a wide range of results, even for similar electrochemical systems. Theoretical predictions suggest the capacitance-potential curve should exhibit bell- or camel-shaped curvature depending on the nature of the IL. Experimental observations have demonstrated several functional shapes such as U-shaped, bell-shaped, camel-shaped, and relatively featureless responses. Much of the work in this thesis starkly contrasts theoretical expectations by demonstrating capacitive behavior that is analogous to high temperature molten salts and dilute aqueous electrolytes with metallic and non-metallic electrode materials. However, our systematic studies of a model IL electrochemical system reveal that there are several ‘user-defined’ experimental variables (i.e. potential scan direction, data acquisition protocol, experimental technique, and potential range probed) which in some instances can significantly impact the resulting capacitance curvature. Some of these variables are often overlooked in the literature and our efforts are aimed at uniting the scientific community in this area to help better compare and understand results. An additional experimental variable of importance is the sorption of water into ILs, which is nearly impossible to prevent due to their hygroscopic nature. The presence of water is known to have a significant effect on the resulting mixtures’ bulk and interfacial properties. While the interaction between ILs and water can significantly vary depending on the nature of the IL, this thesis demonstrates that within small quantities (e.g., < 5000 ppm) of sorbed water there are only minor changes in spectroscopic and electrochemical responses. Collectively, the work outlined in this thesis helps the scientific community better understand electrochemical measurements in IL solvents by examining key analytical variables associated with capacitive measurements. The fundamental electrochemical studies described in this thesis demonstrate that the solid-liquid interface for IL solvents is response to even subtle changes in surface chemistries. These governing interfacial properties have ramifications in myriad applications from energy storage to lubrication.

Thesis (M.S.)--State University of New York at Binghamton, Department of Electrical and Computer Engineering, 2006. / Includes bibliographical references.

In this work the electrostatics of the pneumatic conveying of granular materials in a non-conducting (PVC) vertical pipe is studied using Electrical Capacitance Tomography (ECT) system. The non-conducting wall in general attains static charges arising from particle-wall collisions in the initial periods of conveying process and then reaches equilibrium with the surroundings. The polarity of particles and conveying pipe inner wall agrees reasonably well with the contact potential difference measurements. The perturbations in the capacitance signal due to charge accumulation are larger with smaller air superficial velocity. The denser flow regimes give larger wall residual charge. Wall charging process shows similar trend by surface potential and ECT measurements. The addition of small amount (0.5% by weight) of anti-static agent (Larostat-519) in the powder form decreases the electrostatic charge generation by altering the patterns for particle-particle and particle-wall collisions. / Singapore-MIT Alliance (SMA)

Current municipal solid waste (MSW) practices have encouraged rapid waste degradation (stabilization) as an alternative to past methods of isolating the waste from the surrounding environment. There are challenges to rapid-stabilization technology, in particular, the management of the in-situ MSW moisture content.<p> The primary objective of this study was to evaluate the use of capacitance moisture probes for the purpose of measuring the moisture content within MSW. Capacitance moisture probes have not previously been used in MSW, however their use in agriculture is extensive and knowledge of their potential for monitoring MSW is limited.<p> The specific objectives of this research were to: i) establish a laboratory based correlation between sensor data and volumetric moisture content in MSW, ii) establish a correlation between field-installed capacitance sensors and moisture content derived from continuous-depth in-situ sampling of MSW, and iii) demonstrate the ability of capturing advancing/receding moisture fronts with the field-installed capacitance sensors.<p> Laboratory trials were conducted using hand-compacted MSW at volumetric moisture contents ranging from 15%-55% and a manual type of capacitance sensor. This series of laboratory trials successfully produced a correlation between sensor output and volumetric moisture content.<p> To evaluate the sensors in a real-world application, two configurations of capacitance moisture probes were installed in the field: i) an in-place, continuous-time capacitance probe, and ii) a portable, continuous-depth at discrete time, capacitance probe.<p> Field results indicated that capacitance moisture probes were able to capture the passing of both an artificially and naturally induced moisture front, though quantitative correlation between the in-situ moisture content of the sampled MSW and the readings of the sensors could not be achieved.<p> The reasons for this were a combination of three factors:<p> 1. The introduction of void-space during sensor installation significantly reduced sensor output;<p> 2. Poor MSW sampling technique resulted in 57% recovery (causing the exact origin of samples to be unknown); and<p> 3. The sampling technique disturbed the MSW samples, resulting in incorrect volumetric moisture contents in the samples.

Current municipal solid waste (MSW) practices have encouraged rapid waste degradation (stabilization) as an alternative to past methods of isolating the waste from the surrounding environment. There are challenges to rapid-stabilization technology, in particular, the management of the in-situ MSW moisture content.<p> The primary objective of this study was to evaluate the use of capacitance moisture probes for the purpose of measuring the moisture content within MSW. Capacitance moisture probes have not previously been used in MSW, however their use in agriculture is extensive and knowledge of their potential for monitoring MSW is limited.<p> The specific objectives of this research were to: i) establish a laboratory based correlation between sensor data and volumetric moisture content in MSW, ii) establish a correlation between field-installed capacitance sensors and moisture content derived from continuous-depth in-situ sampling of MSW, and iii) demonstrate the ability of capturing advancing/receding moisture fronts with the field-installed capacitance sensors.<p> Laboratory trials were conducted using hand-compacted MSW at volumetric moisture contents ranging from 15%-55% and a manual type of capacitance sensor. This series of laboratory trials successfully produced a correlation between sensor output and volumetric moisture content.<p> To evaluate the sensors in a real-world application, two configurations of capacitance moisture probes were installed in the field: i) an in-place, continuous-time capacitance probe, and ii) a portable, continuous-depth at discrete time, capacitance probe.<p> Field results indicated that capacitance moisture probes were able to capture the passing of both an artificially and naturally induced moisture front, though quantitative correlation between the in-situ moisture content of the sampled MSW and the readings of the sensors could not be achieved.<p> The reasons for this were a combination of three factors:<p> 1. The introduction of void-space during sensor installation significantly reduced sensor output;<p> 2. Poor MSW sampling technique resulted in 57% recovery (causing the exact origin of samples to be unknown); and<p> 3. The sampling technique disturbed the MSW samples, resulting in incorrect volumetric moisture contents in the samples.

We report an intriguing giant dielectric and magnetodielectric (MD) response on double perovskite Pr2CoMnO6(PCMO) system. The Arrhenius plot indicates that the origin of giant dielectric is internal barrier layer capacitance. Meanwhile, at the highest applied magnetic field 9T, the giant dielectric constant around Tm ~ 150 K is enhanced almost ~ 20% (at 10 kHz frequency) compared with that at zero field. The observed positive MD effect is considered to be associated with the direct consequence of negative magnetoresistance changes (~ -20% at 150 K) which was calculated by temperature dependent impedance spectras. Concomitantly, a pronounced ferromagnetic ordering is observed near Tc ~ 150 K coinciding with Tm of £`¡¬(T). These experimental results suggest that the magnetoresistive and MD effect response is very strongly by magnetic property of PCMO.