Made available in DSpace on 2014-10-09T12:23:59Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:07:58Z (GMT). No. of bitstreams: 1 01070.pdf: 2677585 bytes, checksum: 886f210d3f6431136fa09330d68b8fa2 (MD5) / Dissertacao (Mestrado) / IEA/D / Faculdade de Filosofia Letras e Ciencias Humanas, Universidade de Sao Paulo - FFLCH/USP

Seven β-triketimine nickel complexes C1-C7 with composition [L1-7Ni(μ-Br)2NiL1- 7][BArF4]2, where L1 = HC{C(Me)=N(2,4,6-Me3C6H2)}3, L2 = HC{C(Me)=N(2,6- Me2C6H3)}3, L3 = HC{C(Me)=N(2,4-Me2C6H3)}3, L4 = HC{C(Me)=N(2-MeC6H4)}3, L5 = HC{C(Me)=N(2,4,6-Me3C6H2)}2{C(Me)=N(2,6-Me2C6H3)}, L6 = HC{C(Me)=N(2,4,6-Me3C6H2)}{C(Me)=N(2,6-Me2C6H3)}2, and L7 = HC{C(Me)=N(2,4,6-Me3C6H2)}{C(Me)=N(2,6-iPr2C6H3)}2 were synthesized from the interaction of nickel(II) bromide with L1-7 in the presence of NaBArF (BArF = [(3,5- (CF3)2C6H3)4B]−). These complexes were then fully characterized by single-crystal X- ray diffraction (XRD), MALDI-MS and elemental analysis. From XRD results, they were found to be five-coordinated dimeric bromide-bridged species [LNi(μ- Br)2NiL][BArF]2. The geometry at nickel was distorted square pyramidal, with the τ parameter in the range 0.05 to 0.28. In addition, an enamine-diimine nickel complex C8: (L2-NiBr2) was synthesized from triketimine ligand L2 and nickel dibromide in THF, thus lacking the weakly co-ordinating BArF anion. This complex was found to be pseudotetrahedral, where only two of the three imine nitrogen atoms co-ordinated. These two nitrogen atoms and two bromine atoms formed the coordination shell of Ni(II). The six-membered ring [Co-N1-C2-C3-C4-N2] adopted a boat conformation. These complexes (C1-C7) were screened in the polymerization of ethylene monomer using methylaluminoxane (MAO) as cocatalyst in toluene as solvent at 30°C. It was observed that the steric and electronic variations conferred on the complexes by ligands L1-7 had a strong influence on the activity and also on the properties of the produced polyethylene. The catalytic activity decreased in the order C2 > C1 > C6 > C5 > C7 in the range 3229 to 271 kg PE (mol Ni)-1 h-1 for a standard set of conditions (3 bar ethylene, 30 ̊C, Al:Ni 2000), while the catalysts C3 and C4, bearing only a single ortho substituents, were inactive under identical conditions. Those conditions also had strong influences on catalyst activity and polymer properties: Al:Ni ratio in the range 500 to 3000 maximized activity at 2000. For the polymerization temperature in the range 20 to 50 °C, the activity was maximized at 30 °C, while the number of branches increased with temperature while Mn decreased due to increased chain transfer. Increasing the polymerization pressure resulted in fewer branches while the molecular weight increased because of high concentration of ethylene monomer. The effect of the nature of the counterion on polymerization activity and on the polymer properties was investigated when ethylene was polymerized by C8 (N,N-Ni) and C2 (N,N,N-Ni). It was found that polyethylene produced by C8 had significantly greater crystallinity (Tm 59 ̊C, 35 branches per 1000 carbons) than that produced by C2 (Tm 36 ̊C, 53 branches per 1000 carbons). The presence of the weakly nucleophilic counterion (BArF) as in C2, may have facilitated chain walking, resulting in a branched polymer, whereas [MeMAO]- (C8) was a slightly more nucleophilic counterion impeding chain walking. Furthermore, activity was also much greater for C2 than for C8. This is the first report of an anion effect on branching.

The distribution of Archean Nickel sulphide deposits reflects tectonic controls operating during the evolution of the granitoid greenstone terrains. Important deposits of komatiitic-affinity are concentrated within, and adjacent to, younger (∼2.7 Ga), rift-related greenstone belts (e.g. Canada, Western Australia and Zimababwe). Two important classes of Archean Nickel sulphide deposits exist, formerly known as "Dunitic" and "Peridotitic", these are now referred to as Group I and Group II deposits, based on their characteristic structure and composition. Mineralization varies from massive and matrix to disseminated, and is nearly always concentrated at the base of the host unit. Primary ores have a relatively simple mineralogy, dominated by pyrrhotite-pentlandite-pyrite, and to a lesser degree millerite. Metamorphic grades tend to range from prehnite-pumpellyite facies through to lower and upper amphibolite facies. Genesis of Group I and II deposits is explained by the eruption of komatiites into rift-phase greenstone belts, as channelized flows, which assimilated variable amounts of footwall rocks during emplacement. Sulphide saturation was dependent on the mode of emplacement and, the amount of sulphidic sediments that became assimilated prior to crystallization. This possibly accounts for variations in ore tenor. The Six Mile Deposit (SMD) in Western Australia, is an adcumulate body of the Group IIB-type, exhibiting disseminated mineralization. The ore has been "upgraded" due to hydration and serpentinization. A profound weathering sequence exists, which was subsequently utilized during initial exploration. Exploration techniques has been focused on Western Australia, as it is here that the most innovative ideas have emerged.

Carbon encapsulated metal nanoparticles are an increasingly important class of materials due to the wide range of electronic, magnetic and mechanical properties they display. However, traditional deposition techniques are often complex or lead to a poor quality film. Ionised magnetron sputter deposition is a promising development to traditional magnetron sputtering which combines film deposition with ion bombardment. By adding an RF powered, inductively coupled plasma positioned between the deposition targets and the substrate, the ionisation fraction of the depositing flux is greatly increased. This additional ion flux can then be controlled through the use of an electrical substrate biasing. This controls the energy flux to the surface and therefore the resulting microstructure. Carbon-nickel thin films were grown by ionised magnetron sputter deposition. The films themselves were characterised using a wide variety of techniques to measure not only their structure but their properties. Additionally, the inductively coupled plasma itself was characterised using a Langmuir probe. It was determined that upon application of a negative substrate biasing, the ion flux to the growing film remained constant, however the energy of the species increased. This resulted in a columnar structure of nickel carbide which coarsened as the bias (and therefore the energy of the ions) was increased. Conversely the application of a positive bias gives a large flux of low energy bombardment. This led to the formation of metallic nickel nanoparticles (? 30 nm diameter) which were surrounded by several layers of ordered graphitic shells forming a so-called "nano-onion" structure. The transition between these phases is a result of an increase in adatom mobility when there is a high flux, low energy ion bombardment which allows the nickel and carbon to phase separate. Upon separating, the nickel templates graphite growth due to their similar bond lengths leading to the formation of the graphitic cages. The transition between these two structures is measured through X-ray diffraction which shows a transition from the hexagonal carbide phase to the cubic nickel phase. This is accompanied by an increase in ordering of the carbon as the bias is increased as measured by Raman spectroscopy. Additionally, it is observed that there is an increase in carbon ordering when a negative bias is applied, due to the additional energy from ion bombardment leading to graphite formation. Magnetic measurements showed a transition from a non-magnetic state when the structures were largely carbide, to a magnetic state when metallic. However at room temperature the structures display superparamagnetic behaviour due to the small size of the particles. Measurements of electronic conductivity showed a negative temperature coeffcient of resistivity for all samples demonstrating no metallic conduction path was present. A large drop in resistivity as the temperature increases was assigned to thermally activated conduction. At low temperatures the conductivity is dependent on tunnelling across small regions of amorphous carbon, while at higher temperatures it is possible to excite the electrons into a conduction band allowing them to conduct more easily.

An investigation was conducted on the mechanisms of bond formation between alloys of nickel and single crystals of alumina. Nickel-titanium, nickel-chromium, and nickel-zirconium powder mixtures were cleaned with purified hydrogen gas at 800°C and were individually melted under vacuum (10⁻⁵ m.m. of Hg) in contact with alumina. Interfacial energy measurements at 1500°C were made by the sessile-drop method. The bond surfaces were examined by X-ray fluorescence and X-ray diffraction techniques. The bond formation in all cases appeared to involve two basic mechanisms - metal solute segregation and interfacial reaction. By interfacial measurements and X-ray fluorescence analyses, the solute atoms, titanium and chromium, were shown to be selectively adsorbed at the metal-ceramic interface. Interfacial reaction products were detected by X-ray diffraction methods. The adsorbed titanium reacted with the alumina to produce an interfacial layer of alpha titanium sesqui oxide (⍺-Ti₂0₃). Adsorbed chromium similarly reacted with the alumina to form an interfacial compound. However, this compound could not be identified. With nickel-zirconium alloys, the violence of the reaction between zirconium and alumina made experimental measurements impossible. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

Crevice corrosion experiments have been conducted on Inconel 600 and Inconel 625 exposed to two principle test solutions of 1 M NaCl and 1 M NaCl + 0.01 M Na₂S₂0₃ (Sodium Thiosulphate) at three temperatures, 22°C, 55 °C and 80°C. The crevice corrosion tests were performed in a corrosion cell which was constructed from PTFE (Polytetrafluoroethylene, Teflon) and Pyrex glass. Features of the cell included the utilization of an artificial Teflon-metal crevice and provisions to monitor crevice corrosion current, active crevice corrosion potential and active crevice pH. Additional experiments included potentiodynamic anodic polarization tests on pure Ni, Alloy 600, and Alloy 625 in bulk solution environments and in simulated crevice solutions. Crevice corrosion morphology and compositional analysis of the corrosion products was studied using a scanning electron microscope equipped with an X-ray energy dispersive spectroscopy (EDS) system. Results show that crevice corrosion rates increase with increasing temperature for Alloy 600 in both principle test solutions. X-ray EDS analysis indicated that an insoluble nickel sulphide corrosion product formed on Alloy 600 in a solution of 1 M NaCl + 0.01 M Na₂S₂0₃. For the Alloy 600, in a solution of 1 M NaCl + 0.01 M Na₂S₂0₃, initiation times were significantly reduced and crevice corrosion propagation rates enhanced, as compared to Alloy 600 in 1 M NaCl. The decrease in initiation times has been attributed to the destabilizing nature of the S₂O₃⁻² species on the passive oxide film. Enhanced propagation rates have been attributed to the presence of H₂S in the crevice solution and the formation of an adsorbed species Ni(H₂S)ads which enhances the anodic dissolution reaction. The H₂S in the active crevice solution originated from the thermodynamically favoured electrochemical reduction of the S₂0₃⁻² species in the active crevice solution. Experiments on Alloy 625, which is alloyed with molybdenum, (Mo), show that it was virtually immune to crevice corrosion as compared to Alloy 600 which is not alloyed with Mo. The resistance of Alloy 625 to crevice corrosion initiation has been attributed to the stabilizing nature of MoO₂ in the passive oxide film. For an actively corroding system, the formation of the molybdate species MoO₄⁻² may act as an anodic inhibitor and effectively enhance the repassivation of the passive film. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

Studies have been made of both the solid state and supersolidus sintering characteristics of spherical cupronickel powders. Observations were made of the structural changes and shrinkage rates in specimens sintered in vacuum and in hydrogen. It was concluded that the early stage of solid state sintering (up to one hour at 1200°C) was dominated by Nabarro-Herring creep. Calculations of the stresses at necks during sintering were consistent with the proposed mechanism. No solute segregation to necks occurred during sintering, contrary to earlier observations by Kuczynski with other copper alloys. When pre-sintered cupronickel powder ( 68 μm) aggregates were heated to a temperature above the equilibrium solidus, melting was nucleated first at high angle grain boundaries (necks) and particle surfaces (voids). Most melting was intragranular, nucleated at interdendritic sites of above-average copper content. Solid-liquid equilibrium was established in less than one minute at the supersolidus temperature. The dihedral angle in the system was less than or equal to zero. Growth of solid grains during supersolidus sintering obeyed a parabolic rate law consistent with a model of growth due to phase boundary reaction-controlled solution and precipitation. Shrinkage during supersolidus sintering proceeded in several distinct stages. Prior to attainment of equilibrium; i.e. within the first minute above the solidus (Stage 1), contraction could be attributed to a melting and melt accommodation sequence, plus flattening by the the local operation of solution and precipitation. Beyond this (Stages 2 and 3) all densification was attributed to solution-precipitation, including grain growth. In the final stage of shrinkage (Stage 3) the rate of contraction was controlled by the rate of escape of gas from closed pores. Comparisons have been made between the supersolidus sintering of cupronickel and the liquid-phase sintering of iron-copper. The processes are seen to have little in common. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

>Magister Scientiae - MSc / This thesis reports on the syntheses of new bimetallic iminopyridyl nickel(II) and palladium(II) complexes as catalyst precursors for ethylene ligomerization/polymerization. Tetrahydrophenyl-linked iminopyridyl ligands, pyridin-2-ylmethyl-{4-[(pyridin-2-ylmethylimino)-methyl]-benzylidene}-amine (L1) and (2-pyridin-2-yl-ethyl)-{4-[(2-pyridin-2-yl-ethylimino)-methyl]-benzylidene}-amine (L2) were prepared via condensation from terephthaldehyde and 2 molar equivalents of a primary pyridylamine. Alkyl-linked iminopyridyl ligands N,N'-bis-pyridin-2-ylmethylene-propane-1,3-diamine (L3), N,N'-bispyridin- 2-ylmethylene-butane-1,4-diamine (L4) and N,N'-bis-pyridin-2-ylmethylenepentane- 1,5-diamine (L5) were prepared by condensation of 2 equivalents of 2- pyridinecarboxaldehyde and a primary diamine. The ligands were obtained as either red oils or orange solids. These ligands were characterized using Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), mass spectrometry (MS), elemental analysis (EA), ultraviolet-visible spectrophotometry (UV-Vis) and thermal gravimetric analysis (TGA) where applicable. The tetrahydrophenyl-linked iminopyridyl ligands were subsequently used to prepare their corresponding homobimetallic palladium(II) and nickel(II) complexes. A 1:2 reaction of the ligands with PdCl2(COD), NiCl2(DME) and NiBr2(DME) gave palladium(II) and nickel(II) complexes C1-C6 in moderate to very good yields (58-94%). The palladium(II) complexes were found to be stable, but light-sensitive solids while the nickel(II) complexes were found to be stable, but light and air sensitive solids. These complexes were characterized using FTIR, NMR, EA, MS, UV-Vis and TGA. These complexes were then tested for catalytic activity of ethylene oligomerization. It was found that complexes C1 and C5 were highly active when activated by the cocatalysts methylaluminoxane (MAO) as well as ethyl aluminium dichloride (EADC). It was found that EADC gave the highest activity so the remaining catalysts (C3 and C6) were tested exclusively with EADC. All four complexes were active for ethylene oligomerization with yields of between 2.7-6.5 g, with C5 providing the highest activity and C1 the lowest. These catalysts were highly selective towards C4 oligomers with percentages ranging from 71-81%. Optimization studies were then carried out with C3 by varying the pressure and Al:Ni ratio.

Cross-coupling, which relies on the use of transition metals, is among the most utilized chemical means of establishing carbon-carbon or carbon-heteteroatom bonds between appropriately functionalized sp, sp2, or sp3 centres. However, most cross-coupling reactions rely on the use of palladium to synthesize valuable synthetic targets. This is problematic for the chemical industry as palladium is limited in supply and expensive. Chemists have therefore sought to replace palladium with first-row transition metals (e.g., iron, cobalt and nickel) and recent reports on cobalt and nickel catalyzed cross-coupling reactions indicate that these metals can be used in this capacity. Unfortunately, protocols developed (so far) for these metals are unsuitable for the synthesis of targets with base-sensitive functional groups as they involve strongly basic reaction conditions. Research in this thesis aims to develop both cobalt and nickel pre-formed catalysts that will display high catalytic activity in mildly basic reaction conditions. Current methodologies for cobalt and nickel cross-coupling reactions use either phosphine ligands or NHC ligands of moderate steric bulk (IMes or IPr). Recent advancements in the development of Pd-PEPPSI catalysts have demonstrated that both pre-forming the catalyst and using larger NHC ligands (IPent, IPentCl, or IHept) are required for high catalytic activity in weakly basic conditions. Thus, it was hypothesized that the development of pre-formed cobalt and nickel NHC complexes analogous to their Pd counterparts would improve reactivity in Negishi, Suzuki-Miyaura, and Buchwald-Hartwig amination cross-coupling reactions. Co(IPent)Cl2(Pyr), Co(IPentCl)Cl2(Pyr), and Co2IPr2(OAc)4 were prepared, identified by X-ray crystallography, and evaluated in preliminary Negishi cross-coupling reactions. These complexes were found to be ineffective, but Co2IPr2(OAc)4 was found to be effective for Suzuki-Miyaura cross-coupling. A base screen was performed to enable the use of weak bases, however, the reaction only worked by pre-forming the boronate with n-BuLi, rendering the reaction conditions intolerant of base-sensitive functional groups. [Ni(IPr)]2(µ-Cl)2 , Ni(IPr)Cl(allyl), and Ni(IPent)Cl(allyl) complexes were synthesized and evaluated in Buchwald-Hartwig aminations. Several bases were examined for these reactions but only sodium tert-butoxide was found to be effective. The presence of TEMPO and BHT in these transformations proved deleterious suggesting the involvement of radical intermediates. Finally, stoichiometric reactions were performed to isolate intermediates in the catalytic cycle, supporting the formation of nickel(0).

As atmospheric carbon dioxide (CO2) levels continue to rise due to anthropogenic fossil fuel utilization, the need to develop and employ alternative energy carriers becomes more and more critical. In recent years, interest in hydrogen (H2) has significantly increased as it is a clean and sustainable, alternative fuel, which can be both produced and utilized without greenhouse gas emissions; H2 can be produced via water electrolysis powered by renewable energy sources (RES), such as wind and solar energy, then, H2 can be utilized as a fuel in a hydrogen fuel cell, emitting only water as a by-product. Not only is H2 a clean alternative fuel, but it also provides an economically feasible way of storing renewable energy so that RES supply can be better regulated according to demand. Of the existing water electrolysis technologies, not many offer the ability to produce hydrogen both efficiently and at low cost. The alkaline environment of the more commonly employed traditional alkaline electrolyser allows for the use of non-noble metal electrocatalysts, as well as inexpensive cell materials. This process however suffers from an inefficient cell design. Conversely, the proton exchange membrane water electrolyser (PEMWE) utilizes a solid polymer electrolyte membrane, which allows for a compact, low resistance cell design. However, the harsh acidic environment of this device requires expensive platinum group metal (PGM) catalysts and expensive cell components. Anion exchange membrane water electrolysis (AEMWE) is a promising technology for low-cost, efficient H2 production as it combines the compact cell design of the PEMWE with the favourable alkaline environment of the traditional alkaline electrolyser. The electrochemical water splitting process is limited by the kinetically unfavourable oxygen evolution half-cell reaction (OER), which requires expensive rare catalysts such as iridium, to efficiently carry out the reaction. Nickel (Ni) is a promising inexpensive and abundant catalyst for the OER in alkaline media, due to its high activity and corrosion resistance. A significant increase in OER activity can be achieved by iron (Fe) incorporation into Ni catalysts. The addition of ceria (CeO2), a mixed ionic-electronic conductor with favourable oxygen storage and release properties, can also have a positive effect on catalytic performance. While developing electrocatalysts for improved OER performance is important, evaluating the studied materials as anodes in practical AEMWE devices is imperative as it accounts for the efficiency of the catalysts in electrode layers formed using an anion exchange ionomer (AEI). An AEI is a solid polymer electrolyte that serves as a binder for the particles as well as a hydroxide ion conductor in a catalytic layer of an AEMWE. The main objectives of this thesis are to (i) develop highly active NiFe-based nanoparticle (NP) catalysts with and without CeO2 for the promotion of the OER in AEMWE devices, and (ii) study the effects of commercial AEI type and amount on the efficiency of the produced NiFe-based particles in AEMWE anodes. These objectives will help further understand the behaviour of Ni-based catalysts in AEMWE systems, as well as the effects that catalyst-ionomer interactions can have on anode efficiency in carrying out the OER. The nanoparticles developed in this work were synthesized by an easily scalable chemical reduction method in ethanol using sodium borohydride. Results show that Ni NPs, which are around 4-6 nm in size, with 10 and 20 at% Fe, provide the highest OER performance. Incorporating small amounts of CeO2 into the NiFe materials results in better charge and mass transfer of the catalysts, however it introduces an additional ohmic resistance, which prevails over any OER-promoting interactions between NiFe and CeO2. The best NiFe-based catalysts with and without CeO2 were evaluated as anodes in a single cell AEMWE in combination with the commercial Fumatech Fumion® ionomer as well as the commercial Ionomr Innovations AemionTM ionomer. The single-cell AEMWE analysis of the various catalytic layers shows that Ni90Fe10 with 15 wt% Fumion® shows the best catalytic performance of 1.72 V at 0.8 A cm-2 in 1 M potassium hydroxide (KOH) at 50°C. Ni90Fe10 is also the most stable under operating conditions in comparison to the other tested Ni-based materials. While it was found that using 7 wt% AemionTM provided similar catalytic activity to 15 wt% Fumion®, results show that the AemionTM ionomer interacts with NiFe to inhibit the formation of NiOOH, the OER active phase. The results of this work highlight the complex interactions between Ni-based nanoparticles and anion exchange ionomers towards the OER and provide possible directions for future research and development in high performing Ni-based anodes for AEMWE.