Thesis (M.S.)--Ohio University, August, 2004. / Includes bibliographical references (p. 141-148)

Thesis (M.S.)--Ohio University, August, 2004. / Title from PDF t.p. Includes bibliographical references (p. 141-148)

The 'high-pressure' atmospheric (TIG) arc plasma is studied by means of a multi-Langmuir probe system. In order to determine the appropriate regime of operation, definitions of the plasma parameters for the description of the argon arc are considered and evaluations are presented. A description of the probe basic techniques is followed by an in-depth discussion of the different regimes of probe operation. The emphasis is put on atmospheric and flowing (arc) regimes. Probe sheath theories are compared and “Nonidealities” like cooling due to plasma-probe motion and probe emission mechanisms are then described. The extensive literature review reveals that the existing probe theories are inappropriate for a use in the TIG arc, because of ‘high’ pressure (atmospheric), broad range of ionization across the arc, flowing conditions, and ultimately, to the uncertainty about onset of Local Thermodynamical Equilibrium. The Langmuir probe system is built to operate in floating and biased conditions. The present work represents the first extensive investigation of electrostatic probes in arcs where the experimental difficulties and the primary observed quantities are presented in great detail. Analysis methodologies are introduced and experimental results are presented towards a unified picture of the resulting arc structure by comparison with data from emission spectroscopy. Results from different measurements are presented and comparison is made with data on TIG arcs present in literature. Probe obtained temperatures are lower than the values obtained from emission spectroscopy and this ‘cooling’ is attributed to electron-ion recombination. However, it is believed that probes can access temperatures regions not attainable by emission spectroscopy. Only axial electric potential and electric field are obtained because of the equipotential-probe requirement. Estimations of the sheath voltage and extension are obtained and a qualitative picture of the ion and electron current densities within the arc is given.

Submitted by ALONSO HERNAN RICCI CASTRO null (alonso_elfisico@yahoo.com) on 2017-08-17T17:22:54Z No. of bitstreams: 1 Castro_AHR_PHD.pdf: 57242725 bytes, checksum: 36378feb1c1464a31ab9ed5824539173 (MD5) / Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-08-23T17:50:32Z (GMT) No. of bitstreams: 1 castro_ahr_dr_guara.pdf: 57242725 bytes, checksum: 36378feb1c1464a31ab9ed5824539173 (MD5) / Made available in DSpace on 2017-08-23T17:50:32Z (GMT). No. of bitstreams: 1 castro_ahr_dr_guara.pdf: 57242725 bytes, checksum: 36378feb1c1464a31ab9ed5824539173 (MD5) Previous issue date: 2017-06-26 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este trabalho teve como objetivo o estudo dos parâmetros que influenciam o comportamento de um jato de plasma em pressão atmosférica e sua aplicação em deposição de filmes poliméricos. Com esta finalidade, foram utilizadas duas diferentes configurações de eletrodos em jatos de argônio: um de eletrodo anular externo e outro com eletrodo cilíndrico interno. Também foram utilizadas três geometrias diferentes de bocal de saída do jato (cônico fechado, reto e cônico aberto), usando um eletrodo cilíndrico interno. Os jatos de plasma de argônio operam em modo filamentar, com os filamentos se espalhando por todo o volume do tubo dielétrico, disposto coaxialmente ao eletrodo. Neste trabalho também foi desenvolvido um jato de plasma para a deposição de filmes poliméricos, constituído de um eletrodo de alta tensão em forma cilíndrica localizado no eixo longitudinal do jato, e um eletrodo aterrado na forma de anel que está fixado ao redor do bocal do jato. O estudo foi iniciado com a comparação de dois métodos utilizados para o cálculo da potência. Para os dois jatos de plasma observou-se que o método mais adequado para calcular a potência de descarga é o método da figura de Lissajous, que fornece um erro experimental menor que 3 %. Após realizar a caraterização elétrica dos jatos de plasma, pode-se observar que a potência e a forma de onda da corrente dependem de diferentes parâmetros, que são apresentados em ordem da maior a menor influência da distância bocal-substrato, do fluxo de gás, do tipo de substrato e da geometria do bocal. A deposição de filmes poliméricos foi influenciada pela geometria do jato de plasma e do fluxo dos gases. Os filmes depositados sem movimento do substrato apresentam uma taxa de deposição de 1 m/min. A análise XPS mostrou que os filmes são constituídos em sua maioria por grupos alifáticos C-C/C-H e em menor proporção por hidroxila, éster e ácido carboxílico. Mediante a implementação de uma plataforma móvel foi possível depositar filmes poliméricos em uma grande área, o que amplia a gama de aplicações dos jatos de plasma desenvolvidos neste trabalho. / The goal of this work was to study the parameters which influence the electrical behavior of a atmospheric pressure plasma jet and its application for polymeric films deposition. For this purpose, two different configurations of electrodes were used in argon jets: one with an external annular electrode and the other with an internal cylindrical electrode. Also, three different jet nozzle geometries were adopted using an internal cylindrical electrode: tapered nozzle, straight nozzle and enlarged nozzle. The argon plasma jets operate in filament mode, with the filaments spreading throughout the volume of the dielectric tube, arranged coaxially to the electrode. On this work, a plasma jet system was developed to deposit polymer films, this system consists of a cylindrical high voltage electrode located in the longitudinal axis of the jet, and a grounded electrode in the form of a ring that is fixed around the nozzle of the jet. The study started comparing both methods for calculation of the power of plasma jets. Afterwards, it was concluded that the best method was the Lissajous method giving 3 % of experimental error. After electrical characterization of the plasma jet it was found that the power and current were influenced by different parameters, presented in order of their importance: distance, gas flow, type of substrate and nozzle geometry. The polymer films deposition was influenced by the plasma jet geometry and the gas flow. The films deposited without movement have 1 m/min of deposition rate. The XPS analysis shows that the films are made mostly from aliphatic groups C-C/C-H and in lesser extension by hydroxyl, ester and carboxylic acid. Through implementation of mobile platform was possible to deposit polymer films over larger area.

A cold atmospheric pressure plasma source was investigated as an alternative pre-treatment for carbon fibre reinforced epoxy substrates prior to bonding. For reference, common surface pre-treatments were also investigated (peel ply, manual abrasion, and grit blasting). In the aerospace industry, the peel ply, is usually added to one side of the composite surface during manufacture and peeled off prior to bonding. Peel ply can be used independently or in combination with other techniques. The strength of the bonded joints of the different pre-treatments was assessed through tensile lap shear tests. It was found that combining peel ply with plasma increased the joint strength by 10% whereas manual abrasion or grit blasting after peel ply improved the strength of the joints by 15% and 20% respectively. The effect of pre-treating the composite substrate side without peel ply (bag side) was also investigated. The strength of the joints produced without any pre-treatment was increased by 99% for manual abrasion, 134% for grit blasting and by 146% for plasma. Comparing both surfaces of the composite substrates, it was found that using peel ply improved the performance of the joints by 91%. In order to understand better the effects of the different pre-treatments, surface characterisation of the substrates (surface roughness, surface free energy, and analysis of chemical changes) was also conducted. The effect of roughness did little to affect the strength values (for both surfaces of the composite). The adhesive used in this research was very good at wetting the surface, regardless of the roughness. However, when the adhesive was able to wet the surface, the relationship between bond strength and surface free energy was unclear. Plasma was shown to increase levels of oxygen at the surface and reduce/eliminate the concentration of fluorine at the surface on the bag side of the composite.

Un grand nombre d’applications de plasmas à pression atmosphérique sont en développement. Une obtention de plasma à haute réactivité chimique pour un faible coût énergétique est possible par l’utilisation de décharges nanosecondes répétitivement pulsées (DNRP).Cette recherche concerne plus particulièrement l’effet des NRPD en combustion assistée par plasma. Cette dernière permet l’utilisation de flammes pauvres, qui produisent moins de NOx et qui sont par conséquent moins polluantes.Pour comprendre les phénomènes physico-chimiques qui régissent les NRPD, différents diagnostiques optiques et mesures électriques ont étaient mis en place.L’efficacité de la combustion est très sensible à l’oxygène atomique (O). Nous avons présumé dans nos travaux que la production de cette oxygène ce faisant via un mécanisme a deux étapes où l’azote de l’air produis par impact électronique de l’azote excité aux états (A,B,C), qui réagis ensuite avec l’oxygène moléculaire donnant de l’oxygène atomique.Les densités d’états excités N2(B) et N2(C) on été déterminées par spectroscopie d’émission. L’état N2(A) est lui mesure par spectroscopie d’absorption en cavité résonnante. L’évolution de la concentration de l’oxygène atomique est déterminée par TALIF et on a noté jusqu'à 50% de dissociation de l’oxygène moléculaire en oxygène atomique. Des mesures résolues spatialement et temporellement ont été effectuées. L’élévation de la température du gaz dans la décharge a été établie. Des mesures électrique de tension et de courant ont permis l’estimation de l’énergie déposée par pulse.En résume ses mesures nous ont permis de mieux comprendre et de caractériser une DNRP dans l’air. Le fait que les temps de décroissance et les valeurs de l’évolution des concentrations des états excités de l’azote coïncident avec ceux de la production de l’oxygène atomique et que le gaz voit sa température s’élever de quelques centaines de degrés tendent à valider le mécanisme à deux étapes proposé. / In the last decade, nanosecond repetitively pulsed discharges (NRPD) had became very popular, because they allow to produce high electron densities and active species for an energy efficiency unequalled in air at atmospheric pressure.This thesis targets more particularly the effect of the NRP discharges in plasma-assisted combustion. NRP discharges can stabilize low temperature flames, which produce fewer NOx and are consequently less polluting. Few studies have investigated the mechanism of action of the plasma on flames.We have studied the kinetic mechanism of the atomic oxygen production, known as “two-step” or “ultrafast” mechanism. Where the nitrogen excited states (states A3Su,+, B3Pg, C3Pu) produced by electron impact during the 10ns-pulse dissociate oxygen with a heat release.To this end, various optical diagnostic techniques and electrical measurements, with time and space resolution of nanoseconds and hundreds of micrometers, have been set up.Densities of the excited states N2(B) and N2(C) have been determined by quantitative emission spectroscopy. The density of N2(A) state, was measured by a sensitive detection technique, Cavity-Ring Down Spectroscopy (CRDS). Finally the time evolution of the density of atomic oxygen was determined by Two-Photon Absorption Laser Induced Fluorescence or TALIF. In addition, an increase of the gas temperature related to the two-step mechanism was determined by emission spectroscopy.The work of this thesis represents the first experimental confirmation of the two-step mechanism suggested in the literature. At atmospheric pressure, this mechanism is found to dissociate up to 50 % of molecular oxygen and heats the gas by about 1000 K.As a summary, the work of this thesis allowed characterizing and better understanding nanosecond repetitively pulsed discharges in the air at atmospheric pressure and determining the production on the key active species, atomic oxygen.

Dans cette thèse nous avons étudié l'influence de surfaces diélectriques sur la dynamique de propagation de décharges à pression atmosphérique. Tout d'abord, pour les simulations 2D réalisées dans ce travail, nous avons optimisé les performances du code de décharge en utilisant des schémas numériques performants et des techniques de parallélisation. Nous avons ensuite étudié la dynamique de propagation d'une décharge dans l'air à pression atmosphérique dans une géométrie pointe-plan avec un plan diélectrique sur la cathode. Puis, nous avons étudié l'influence d'un obstacle plan diélectrique sur la dynamique de propagation d'une décharge. Nous avons montré que selon les caractéristiques du diélectrique, l'amplitude et la polarité de la tension appliquée, une seconde décharge peut s'initier ou pas dans l'air derrière le diélectrique. La comparaison des résultats avec les expériences a montré que dans une géométrie pointe-plan avec une pointe fine et une tension très élevée, une seule décharge de forme conique est observée. Un bon accord est obtenu sur le diamètre de la décharge et sa vitesse de propagation. Avec un obstacle plan diélectrique entre les électrodes, la dynamique de ré-allumage est plus rapide dans les simulations. Pour améliorer la comparaison avec les expériences, nous avons étudié l'influence de plusieurs processus physico-chimiques. Pour finir, nous avons étudié la dynamique de décharges à pression atmosphérique dans des tubes diélectriques. Pour un mélange He-N2, nous avons montré l'importance des réactions à trois corps. Enfin, nous avons montré l'influence du diamètre du tube sur la structure des décharges dans un mélange He - N2 et dans l'air. / In this Ph.D. thesis, we have carried out 2D numerical simulations to study the influence of dielectric surfaces on the propagation dynamics of plasma discharges at atmospheric pressure. First we have improved the computational efficiency of the discharge code used in this work in implementing parallelization techniques and more efficient numerical schemes. Second we have studied the dynamics of an air discharge at atmospheric pressure in a point-to-plane geometry with a dielectric layer on the cathode plane. Then, we have studied the influence of a dielectric layer obstacle in the inter-electrode gap. We have shown that depending on the characteristics of the dielectric layer and the amplitude and polarity of the applied voltage, a second discharge may reignite or not below the dielectric in the second air gap. The comparison of simulation results with experiments has shown that in a point-to-plane geometry with a sharp point and a high over-voltage, a single conical discharge structure is observed. A good agreement on the discharge diameter and propagation velocity has been obtained. With a dielectric obstacle in the gap, the simulated reignition dynamics is faster than in the experiments. To improve the agreement, we have studied the influence of several physico-chemical processes. Finally, we have studied the dynamics of discharges in dielectric tubes at atmospheric pressure. For a He -N2 mixture, we have put forward the importance of three body reactions. Last, the influence of the tube radius on the structure of discharges in He - N2 and air is discussed.

Radio frequency (rf) atmospheric pressure glow discharges (APGDs) have received growing attention for their exciting scope of new science and their immense potential for widespread applications. While geometrically similar to conventional low-pressure discharges used in the semiconductor industry for decades, rf APGDs present new physics that require investigation. This thesis presents an experimental and computational study of helium rfAPGDs aimed at making a contribution to the current understanding of these discharges and enabling their optimization for different applications. The timely interest and significance of this work is highlighted by the publication of different parts of this thesis in 10 peer-reviewed international journals. Starting with the electron trapping in rf APGDs, the thesis looks into the electron heating mechanism responsible for sustaining the discharges, the influence of the rf excitation frequency on the discharge characteristics, the role of impurities in the discharge chemistry as well as the evolution of the discharge as the size is reduced down to microplasma dimensions. The findings of this research are based on the synergistic use of electrical measurements, optical diagnostics and self-developed computational models. With the knowledge gained from this thesis, rf-APGDs can be readily used for a wide-range of applications including biological decontaminations, nanostructure fabrication and portable gas analyzers.

With 663 million people still without access to an improved drinking water source, there is no room for complacency in the pursuit of Sustainable Development Goal (SDG) Target 6.1: “universal and equitable access to safe and affordable drinking water for all” by 2030 (WHO, 2017). All of the current efforts related to water supply service delivery will require continued enthusiasm in diligent implementation and thoughtful evaluation. This cannot be over-emphasized in relation to rural inhabitants of low-income countries (LICs), as they represent the largest percentage of those still reliant on unimproved drinking water sources. In that lies the motivation and value of this thesis research- improving water supply service delivery in LICs. Manually operated suction pumps, being relatively robust, low cost, and feasible to manufacture locally, are an important technology in providing access to improved drinking water sources in LICs, especially in the context of Self-supply. It seems widely accepted that the water-lifting limit of suction pumps as reported in practice is approximately seven meters. However, some observations by our research group of manually operated suction pumps lifting water upwards of nine meters brought this “general rule of thumb” limit into question. Therefore, a focused investigation on the capabilities of a manually operated suction pump (a Pitcher Pump) was conducted in an attempt to address these discrepancies, and in so doing, contribute to the understanding of this technology with the intent of providing results with practical relevance to its potential; that is, provide evidence that can inform the use of these pumps for water supply. In this research, a simple model based on commonly used engineering approaches employing empirical equations to describe head loss in a pump system was used to estimate the suction lift limit under presumed system parameters. Fundamentally based on the energy equation applied to incompressible flow in pipes, the empirically derived Darcy-Weisbach equation and Hydraulic Institute Standards acceleration head equation were used to estimate frictional and acceleration head losses. Considering the theoretical maximum suction lift is limited to the height of a column of water that would be supported by atmospheric pressure, reduced only by the vapor pressure of water, subtracting from this the model was used to predict the suction lift limit, also referred to herein as the practical theoretical limit, assuming a low (4 L/min) and high (11 L/min) flow rate for three systems: 1) one using 1.25-inch internal diameter GI pipes, 2) one using 1.25-inch internal diameter PVC pipes, and 3) one using 2-inch internal diameter PVC pipes. In all considered cases, with an elevation equal to sea level, the suction lift limit was estimated to be over nine meters. At a minimum, the suction lift limit was estimated to be approximately 9.4 meters for systems using 1.25-inch internal diameter pipe and 9.8 meters for systems using 2-inch internal diameter pipe, with essentially no discernable effects noticed between pipe material or pipe age. Additionally, laboratory (field) trials using a Simmons Manufacturing Picher Pump and each of the aforementioned pipe specifications were conducted at the University of South Florida (Tampa, FL, USA) to determine the practical pumping limit for these systems. Results from the pumping trials indicated that the practical pumping limit- the greatest height at which a reasonable pumping rate could be consistently sustained with only modest effort, as perceived by the person pumping- for a Pitcher Pump is around nine meters (9 meters when using 1.25-inch internal diameter GI or PVC pipe and 9.4 meters when using 2-inch internal diameter PVC pipe). Therefore, results from this research present two pieces of evidence which suggest that the practical water-lifting limit of manually operated suction pumps is somewhere around nine meters (at sea level), implying that reconsideration of the seven-meter suction lift limit commonly reported in the field might be warranted.

If the analyses of trace components in complex organic samples are to be optimised, then these compounds must be isolated either physically or chemically from surrounding matrices. Ion mobility spectrometry (IMS) is an analytical technique used worldwide for the detection of on-site trace compounds. The technique can be optimised to isolate the target species from complex matrices through both physical separation, based on the mobility of the analyte ions at ambient pressure, and chemical discrimination through preferential ionisation of the target. Optimisation of the latter is commonly achieved through doping the spectrometer with a selective reagent gas, termed a dopant. The chemical processes required to optimise the responses of target analytes are dependent on the identity and concentration of the dopant. As such, a variety of dopants have been successfully implemented in ion mobility spectrometers. The technology for the deliverance of dopants in IMS is commonly through permeation sources, which provide a stable chemical environment in the ion mobility cell. Althoughrelatively inexpensive and durable, these devices are difficult to change and generally deliver a single dopant concentration. As a result, only one type of chemistry is possible and the responses cannot be optimised for a range of analytical applications. Such limitationsbecome increasingly significant when IMS is hyphenated to a chromatograph where a range of different dopant conditions may be sought over the course of a chromatographic run. This thesis sought to overcome these limitations through the development and implementation of piezoelectric dispensers, interfaced directly to the transport gas regions of IMS cells. The study demonstrates for the first time the ability to use piezoelectric dispensing as a dopant introduction methodology in IMS for controlling and calibrating a range of dopant chemistries. 2-butanol, acetone, dichloromethane, 1-chlorohexane, 4-heptanone and 1-bromohexane were the candidate dopants chosen for the studies, covering a wide range of physical and chemical properties. The novel technology was used to dispense the target dopants into IMS cells at concentration ranges over three orders of magnitude. Dopant chemistries were achieved within three seconds from the point of dispensing, administered in drop-ondemand formats, and could be delivered either transiently or at steady-state concentrations. The concept was validated through integrated spectral dopant responses. In transient control, dynamic linear relationships of R2 = 0.991 - 0.998 were achieved between dispensed dopant mass and peak area. Under continuous operation, the RSD of the dopant level was < 18% for all dopants. Clear out times for dopant responses were in the order of 3-5 seconds, indicating negligible hysteresis effects. The study also proved the concept of controlling monomer and dimer ion chemistries from 2-butanol actuations when interfaced to a differential mobility spectrometer at mass fluxes between 21 - 1230 ng m-3 , and the simultaneous control of dopants in negative and positive ionisation modes to RSDs <10%. This thesis describes the techniques used to optimise the piezoelectric dispensing of the full dopant range, as well as the full design protocols required to interface to mobility spectrometers. The outcomes from these studies provide a realisation for piezoelectric dispensers as a future mainstream dopant introduction technique for the analysis of complex samples.