This thesis examines the use of zinc for electroplating and compares its use to other metals. Experiments conducted to gather data indicated circumstances which resulted in optimal results.

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The aim of this work is to produce a manufacturing strategy for high current (>10 mA) field emission (FE) devices for military (microwave generation) and civilian (particle accelerator electron beam) applications using carbon nanotubes (CNT) as base material. With a particular focus on the relationship of the laser time pulse duration used for cutting CNTs and how this affects the field emission performance. Material selection for this work was narrowed to CNT as they possess unique characteristics such as: high aspect ratio; high thermal conductivity; high chemical stability and high current carrying capacities up to a theoretical limit of 1,200 MA∙cm-1 making them an ideal material for FE. The CNT material studied in this work is produced in two distinct forms, fibres (∅~7-10 μm) and films (h~30 μm), using a floating catalyst chemical vapour deposition process which produces high quantities of CNT material with mixed mechanical and electrical properties. The material is difficult to handle because of its dimensions and is susceptible to environmental changes i.e. electrostatic forces. In order to reduce the variability in electrical properties, a laser purification process was developed. The process consists of locally irradiating an infra-red (IR) laser several microseconds directly at the material. A percentage is vaporised (mainly non-conductive or defective material) and the remaining CNT material shows very high crystallinity with an increase of up to ten times (G/D ratio > 100) compared to the original material and electron mean free path is increased by an order of magnitude. The production strategy is based on directly coating the CNT material with copper using an electroplating process. This allowed for CNT fibre and film to be easily handled and improved the overall electrical contact. Emitter geometry was customised by a laser cutting process to achieve increased enhancement factor geometries, in this case, triangles with 29 tips whilst reducing FE variability. FE performance was quantified by testing the devices in a continuous DC mode with a sweep up to 1,000 V until the material suffered catastrophic failure. The gap distance between the tip of the triangles and the anode was varied to increase the electric field until failure. FE results using the production strategy improved more than 400% compared to untreated material. Applications for these devices are intended to be in the creation of high energy electron beam lines and generation of high powered directed microwaves.

Resumo: Os revestimentos de zinco são os mais amplamente utilizados na proteção do aço contra a corrosão. Atualmente, estes vêm sendo substituídos por ligas, como o Zn- Ni, pois têm revelado melhores propriedades mecânicas, maior resistência à corrosão quando comparados aos revestimentos de zinco de mesma espessura, além de poderem ser aplicados em temperaturas mais elevadas. Outros revestimentos de ligas de zinco formados com elementos do grupo VIIIB têm se mostrado promissores por apresentarem propriedades semelhantes e protegerem o aço por ação galvânica. Neste trabalho, eletrodepósitos de Zn, Zn-12%Ni, Zn-0,6%Co e Zn-<3%Fe-0,6%Co obtidos sobre aço SAE 1010, a partir de banhos alcalinos comerciais foram tratados por cromatização e caracterizados quanto às propriedades mecânicas, morfologia, comportamento eletroquímico e resistência à corrosão em solução de NaCl 3,5% e na presença de oxi-ânions do grupo VIB. Os estudos foram realizados através de medidas de microdureza, rugosidade, MEV, EDS, DRX e técnicas eletroquímicas. Dentre os eletrodepósitos estudados, o de Zn-Ni mostrou maior valor de rugosidade, enquanto os demais apresentaram resultados próximos aos do substrato de aço. As ligas Zn-Ni e Zn-Fe-Co apresentaram maior dureza em relação ao Zn. Através de DRX foi verificado que os eletrodepósitos são cristalinos, sendo identificada na liga Zn-Ni a presença das fases g (Ni5Zn21) e d (Ni3Zn22), responsáveis pela sua maior resistência à corrosão. As ligas tratadas por cromatização revelaram maior resistência à corrosão, tanto nos ensaios de salt spray, como nos ensaios eletroquímicos. O principal produto de corrosão encontrado sobre os eletrodepósitos, após os ensaios de salt spray e de imersão em solução de NaCl 3,5 %, foi o Zn5(OH)8Cl2.H2O, não sendo detectados óxidos ou hidróxidos formados... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The zinc coatings are the most widely used in protecting steel against corrosion. Currently, these are being replaced with alloys such as Zn-Ni, for they have shown better mechanical properties, higher corrosion resistance when compared to zinc coatings of equal thickness, and can be applied at higher temperatures. Other zinc alloys coatings formed with elements of group VIIIB were shown to be promising because they have similar properties and protect the steel by galvanic action. In this study, electrodeposited Zn, Zn-12% Ni, Zn-0.6%Co and Zn-<3% Fe-0.6% Co coatings obtained on steel SAE 1010, from alkaline baths have been treated with commercial chromate and characterized by the mechanical properties, morphology, electrochemical behavior and corrosion resistance in NaCl 3.5% and in presence of oxy-anions of group VIB. The studies have been performed by measurements of hardness, roughness, optical microscopy, SEM, EDS, XRD and electrochemical techniques. Among the studied electrodeposits, Zn-Ni showed higher roughness, while others showed results similar to the steel substrate. Ni-Zn and Zn-Fe-Co alloys showed higher hardness in relation to Zn. By XRD it has been observed that electrodeposits are crystalline, being identified in Zn-Ni alloy phases presence of g (Ni5Zn21) and d (Ni3Zn22), responsible for its higher corrosion resistance. Alloys treated by chromate have revealed greater corrosion resistance both in salt spray tests and in electrochemical tests. The main corrosion product found on electrodeposits, after salt spray and immersion in 3.5 % NaCl solution tests, was Zn5(OH)8Cl2.H2O, not being detected oxides or hydroxides formed with metals. All electrodeposits protect steel by galvanic action, for they have presented corrosion potentials more negative than that of steel. Chromate or molybdate addition to the electrolyte further extends the stability range, which shows... (Complete abstract click electronic access below) / Orientador: Roberto Zenhei Nakazato / Coorientador: Luis Rogerio de Oliveira Hein / Banca: Marcelo dos Santos Pereira / Banca: Alain Laurent Marie Robin / Banca: Cecílio Sadao Fugivara / Doutor

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The main subject of the thesis is the investigation of palladium-iron alloy electrodeposition from aqueous solutions in general. Palladium-iron alloy deposits could be in principle a substitute for nickel or nickel-palladium deposits to avoid metal dermatitis. Nickel contact dermatitis is an especially sensitive allergy caused by decorative or functional use of nickel: it needs to be avoided in a number of applications. Electrochemical and chemical experiments have been carried out on several solutions with variable pH, salts and metal complexes to design a chemical and electrochemical stable electrolyte for palladium-iron alloy electrodeposition. Electrochemical measurements, physical and chemical analysis techniques, mechanical, optical, chemical and electrochemical measurements methods as well as different corrosion tests were used to describe the electrochemical processes and the properties of the palladium-iron deposits. Investigations have shown that from ammoniacal electrolytes electrodeposition in a wide range of composition is possible (pH = 7.5 - 10.5). Electrolyte consists of palladiurn as Pd(NH3)4CI2 and iron as iron(ill)-citrate. Composition of the deposited alloys depends mainly on the ratio of the metal ions in the electrolyte, while the effect of current density and electrolyte temperature is slight. Current efficiency depends on iron concentration in the electrolyte and is a maximum of ca. 85 %. Palladium-iron alloys with a higher content of palladium (>80.-%) show cracks because of the high internal stress (tensile stress) of those layers. Alloys with smaller content of palladium (<20 wt. -%) are less sensitive to cracking. Wear resistance and corrosion resistance of the palladium-iron alloys are similar or sometimes better to palladium, palladium-silver, palladium-cobalt or palladium-nickel deposits. Hardness of the palladium-iron layers increases with increasing iron content from 200 to 600 VHN. Contact resistance is low in the range of 0.5 to 1.5 mfl and barrier layer properties are excellent for gold and copper diffusion during services up to 160 degrees Celsius for 240 hours.

Thesis (Ph. D.)--West Virginia University, 1999. / Title from document title page. Document formatted into pages; contains xv, 207 p. : ill. (some col.) Includes abstract. Includes bibliographical references (p. 203-207).

Thesis (Ph.D.)--Bioengineering, Georgia Institute of Technology, 2008. / Committee Chair: Stephen P. DeWeerth; Committee Member: Bruce Wheeler; Committee Member: Michelle LaPlaca; Committee Member: Robert Lee; Committee Member: Steve Potter

Thesis (Ph. D.)--Columbia University, 1935. / Vita.