The preparation of a glide path prior to the use of rotary nickel titanium instrumentation reduces torsional stress and the risk of rotary nickel titanium instrument separation. The objective of this in vitro study was to evaluate 3 different glide path preparation techniques in respect of:  Percentage change of curvature from original canal anatomy; and  The occurrence of aberrations in canal anatomy (ledging, zipping and elbows). One hundred and twenty S-shaped Endo-Training-Blocks were selected. The canals were injected with India ink dye. The blocks were indexed with 3 bur marks and placed into a template before pre-instrumentation images were acquired digitally. The blocks were randomly divided into four groups of thirty each. Glide paths were prepared by a single operator with stainless steel hand K-files only, up to ISO size 20 (group 1, control), stainless steel hand K-files in the M4 reciprocating hand-piece up to ISO size 20 (group 2), hand K-files to ISO size 10 then NiTi rotary PathFiles (group 3) and hand K-files to ISO size 10 then NiTi rotary X-Plorer files (group 4). After glide path preparation the blocks were replaced into the template and post-instrumentation images were digitally acquired. Percentage change of curvature from original canal anatomy: Pre-instrumentation and post-instrumentation images were imported into Rhinoceros software to determine the end points of the canal curves and calculate the percentage change of canal curvature for the radii of apical and coronal curves. The data was collected and tabulated. Differences in canal curvature modification were statistically analysed with respect to logarithmic transformed change from baseline using ANCOVA (p<0.001) with logarithmic transformed pre-instrumentation values as covariate. After establishing preparation differences, both for change from baseline (pre-instrumentation) for apical and coronal curves, specific differences were tested using Fisher’s LSD for pairwise comparisons. Prepared groups differed significantly (p<0.001) and in particular, group 1 (Hand K-files) (control) and group 2 xiii (Hand K-files in M4 Safety reciprocating hand piece) differed significantly from all the other groups while group 3 (Hand K-files and PathFiles) and group 4 (Hand K-files and X-Plorer files) did not differ significantly. Group 3 (Hand K-files and PathFiles) and group4 (Hand K-files and X-Plorer files) were also superior to group1 (Hand K-files) (control) and group2 (Hand K-files in M4 Safety reciprocating hand piece). The occurrence of aberrations in canal anatomy (ledging, zipping and elbows): Pre-instrumentation and post-instrumentation images were superimposed using Adobe Photoshop software. The images were imported into a PowerPoint presentation and examined by three different blinded clinicians independently, for the presence of aberrations. There were no differences between the examiners in their assessment of the images. The data was collected and tabulated. The incidence of canal aberrations was analysed using Fisher’s exact test (p<0.05). The groups differed significantly regarding the number of aberrations (p=0.005). In particular, group 1 (control) (Hand K-files) and group 2 (Hand K-files in the M4 reciprocating hand piece) did not differ statistically (p=0.254; 20% and 6.67%). However group 2 (hand K-files in the M4 reciprocating hand piece) also did not differ significantly from group 3 (Hand K-files and PathFiles) and Group 4 (Hand K-files and X-Plorer files) (p=0.326). There were no aberrations detected in the rotary NiTi groups (group 3 and group 4). / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Odontology / unrestricted

In this dissertation electrochemical nickel oxide formation in alkaline solution and the electro-oxidation of glycerol on polycrystalline electrodes are studied as a function of temperature. This is done using electrochemical impedance spectroscopy (EIS), Tafel analysis, cyclic voltammetry, chronoamperometry, and chronopotentiometry among other techniques. Additionally, in order to facilitate the study of aqueous alkaline systems beyond the normal boiling point of water, an electrochemical cell was designed utilizing a self-pressurizing autoclave. This allowed for the study of aqueous alkaline systems up to 140 °C. Product analysis of glycerol electro-oxidation on nickel was performed at various temperatures using HPLC. A reaction pathway for the organic products was determined. At su ciently high temperatures a polymer was discovered. This polymer product was characterized by DLS, DSC, CP-MAS NMR, and ATR-IR and determined to likely be a pseudo-polysaccharide. DSC analysis suggests that the polymer exists as three distinct structures, and DLS analysis suggests that the polymer exists in three di erent size distributions. The lack of a glass transition temperature in the DSC spectrum indicates that it is likely thoroughly cross-linked. The aging process of alpha-Ni(OH)2 to beta-Ni(OH)2 was studied as a function of temperature using cyclic voltammetry and dynamic EIS. This lead to the observation that beta-Ni(OH)2 does not appear to form on the oxide surface at 100 °C and above. A methodology was developed for preferentially stabilizing either beta-NiOOH or gamma-NiOOH on the electrode surface. This methodology was used to determine that beta-NiOOH is the better oxygen evolution catalyst of the two oxide phases. The reversible potential of Ni(OH)2 oxidation was observed to have a shift of -1:14 mV K-1, and this data was used in a thermodynamic analysis to identify the nickel species involved in the reaction. Based on data from the literature the oxidation of NiO or Ni(OH)2 to NiO2 appears to best match the observed data. Mechanistic analysis was performed for glycerol on nickel in alkaline solution using a combination of Tafel analysis, cyclic voltammetry, AC voltammetry, and EIS. This study indicates that glycerol oxidation behaves differently on gamma-NiOOH and beta-NiOOH, perhaps explaining the discrepancy between various pieces of data found in the literature. Tafel analysis led to the observation that there appear to be two di erent glycerol oxidation regimes. Below 80 °C, alpha = 0.5, indicating that the rate determining step is an electron transfer step with no pre-equilibrium electron transfers. At 80 °C and above alpha = 1, indicating that the rate determining step has no electron transfer and one pre-equilibrium electron transfer. This was determined to be caused by the transition of the underlying nickel oxide phase from gamma-NiOOH to beta-NiOOH because the change is retained upon cooling. Additionally, EIS showed two semicircles which indicates the presence of one kinetically signifficant adsorbed intermediate. These observations were incorporated into a detailed proposed reaction mechanism. / Graduate

Includes bibliographical references. / X-ray crystallographic studies have been used to elucidate the structures of two new Werner clathrates. ... The chloroform molecule is disordered, lying on a two-fold axis. Stoicheiometric characterization of the clathrates was determined using various chemical techniques, including mass spectroscopy, proton nuclear magnetic resonance and complex iometric titration. The clathrating phase of the second clathrate was investigated by guest-loss studies on a McBain balance followed by X-ray powder photography. Host-quest non-bonded interactions of both clathrate compounds were studied using atom-pair potentials.

Chlorite is a ferrous silicate mineral occurring as afracture filling mineral in the Swedish granite bedrock thatsurrounds the area of the candidate Swedish geologicalrepositories for nuclear waste. To investigate the importance of chlorites as a naturalbarrier for radionuclide migration sorption of Ni(II) onto anatural chlorite was chosen as the studied system. The sorptionbehaviour was studied using batch technique under differentexperimental conditions by varying the concentration ofbackground electrolyte, pH and initial nickel concentration.Our experiments showed that sorption is dependent of pH; belowpH 4 no sorption occurs and in the pH range 7-11 the sorptionmaxima was found. The sorption shows no dependence of ionicstrength in our experiments and together with pH dependency weconclude that the sorption of nickel to chlorite is mostlyoccurring through surface complexation. The distributioncoefficient, Kd, was determined for our results and in the range formaximal sorption the Kdis approximately 103cm3/g. Our experimental data were described using a diffuse doublelayer model, including strong and weak surface sites, in thesoftware PHREECQ and the results obtained from PHREEQC werealso used for a fit of the data in the software FITEQL. Thesurface complexes that dominate the sorption of nickel tochlorite from our model are Chl_ONi+(weak) and for pH above 9 Chl_ONi(OH)-(weak). Flow-through technique was used in ourinvestigations regarding the dissolution rate of a naturalchlorite and the experimental results show that the dissolutionrate of chlorite is strongly pH dependent and at pH 2 thehighest dissolution rate (RSi) could be determined to 7• 10-11mol/(m2s) based on silica data. Keywords:chlorite, nickel, sorption, surfacecomplexation, dissolution rate.

Different metals and metal complexes have been used as catalysts in many industries such as commodity petrochemicals, fine and specialty chemicals, polymers, environmental services, agrochemicals and pharmaceuticals. Although these catalysts allow for increased reaction rates and selectivity, they can also be toxic, expensive and of limited supply (cf. Pt group metals). This has led researchers to the intensive study of first row metal catalysts, with nickel standing out as the most widely studied to date. As found for other first row metal catalysts, nickel’s easy access to oxidation states 0-3 allows for a number of different one- and two-electron mechanisms and novel transformations. In Chapter 2 we use a phosphine-free, tridentate N,N,N ligand to generate an active catalyst for the C-N cross-coupling reaction of aryl halides with amines. The catalyst demonstrated excellent turnover numbers (up to 484) for the amination reactions that are proposed to proceed through a Ni(I)-Ni(III) cycle. In Chapter 3 we investigate the Ni coordination chemistry of a biomimetic SNS thiolate ligand. Protonation of the Ni bis(thiolate) complex, Ni(-SNS)2, removes one SNS ligand, affording crystals of a thiolate-bridged dimer dication, {[Ni(--SNS)]2}2+ that exhibits unique anionic tridentate ligand dynamics. Dissolving these crystals, even in weakly-coordinating solvents such as dichloromethane, gives a mixture of ‘naked’ Ni2+ and paramagnetic, trinuclear {[Ni(--SNS)2]2Ni}2+. Although this equilibrium lies far to the right (no diamagnetic dication visible in NMR), addition of ancillary ligands proceeds smoothly to provide several mono- and dinuclear Ni thiolate products, [Ni-SNS)L]n – potential bifunctional catalysts for further studies. In Chapter 4 we demonstrate using chemical and electrochemical techniques that one-electron reduction of Ni(-SNS)2 triggers quantitative imine C-C bond coupling, forming [Ni(S2N2)]- with a redox-active ligand. Spectroelectrochemical studies indicated reversible oxidation and reduction steps give three stable redox states, ([Ni(S2N2)]0/-/2-), that were characterized by NMR, EPR and UV-Vis spectroscopy, X-ray diffraction and computational chemistry. While the Ni(0) dianion (and not the Ni(I) anion) reacted reversibly with phenol and carbon dioxide, results from Chapter 5 showed that reactions with strong electron-acceptor fluoroalkenes proceeded more cleanly with the Ni(I) anion. The latter reactions afforded a mixture of fluoroalkenyl and fluoroalkyl products resulting from C-F bond activation and electron transfer/H atom abstraction, respectively. In Chapter 6 we discuss our results in the context of the current state of the art and suggest some avenues for future development.

The aim of this work was to investigate the effects that a magnetic field can induce during the electrodeposition of Ni and Ni-Fe alloys. Special regard was given to mass transport controlled effects. Magnetic field effects on the nucleation and growth of ferromagnetic layers and on the properties of electrodeposited layers (like grain size, texture, morphology or roughness) were investigated. The influence of a magnetic field on the magnetic properties of Ni layers and on the composition of Ni-Fe alloys was also studied. Nucleation and growth of thin Ni layers on gold electrodes under a superimposed magnetic field were analysed in-situ with the Electrochemical Quartz Crystal Microbalance technique. Three theoretical models were chosen for characterizing the Ni nucleation: Scharifker-Hills (SH), Scharifker-Mostany (SM) and Heerman-Tarallo (HT). The AFM images proved that more nuclei appear in a magnetic field in the case that the Lorentz force and the natural convection act in the same direction. From all the models, the HT model gave the best agreement with the AFM results. When the Lorentz force and the natural convection act in the same direction, an increase of the Ni partial current with the magnetic field was obtained. When they act in opposite directions, the Ni current was influenced just at the beginning of deposition (first 10 seconds). At longer times, the magnetic field has no effect on the Ni current. However, the total current (jNi+jHER) decreases with the magnetic field. In the absence of a macroscopic MHD convection, the Ni current decreases with the magnetic field the first 10-15 seconds of deposition. On longer time scales no influence of the magnetic field could be noticed for this configuration. When the magnetic field was applied perpendicular to the electric current, an increase of the hydrogen evolution reaction (HER) with the magnetic flux density was noticed. Hydrogen reduction is mass transport controlled. Therefore, the magnetic field will increase the limiting current of the HER. Optical microscopy images showed that the hydrogen bubbles were circular in the absence of the MHD convection and that they presented a tail when a Lorentz force was present. The direction of the tail depends on the net force induced by the natural and MHD convections. The interplay between the natural and MHD convections proved to be important during Ni-Fe alloy deposition, too. When the Lorentz force and the natural convection act in the same direction, an increase of the Fe content of the alloys with the magnetic field was observed. When the Lorentz force was perpendicular to the natural convection, no significant changes were observed in the composition of the layers. The alloy composition did not change with the magnetic field when the electric current was parallel to the magnetic field lines. Two surfactants were used in the case that Ni was electrodeposited from a sulfamate bath: SDS and sulfirol 8. The Ni layers obtained from a sulfamate bath with sulfirol 8 presented larger grains compared to the layers deposited from a bath free of surfactants. This increase of the grain size was attributed to the incorporation of the surfactant in the deposit. Coarser layers were obtained in a magnetic field (applied perpendicular to the electric current) when the electrodeposition was done from an electrolyte with surfactants. The number of grains increased with the magnetic field for the Ni layers electrodeposited from a bath free of surfactants and for a bath with SDS. As a consequence, the grain size decreased. In the case of the electrolyte with sulfirol 8, the number of grains decreased with the magnetic field, and their size increased. For the Ni-Fe alloys, which contained less than 10 at% Fe, the preferred crystalline orientation changes from (220), in the absence of a magnetic field, to (111), (when the magnetic field was applied perpendicular to the electric current). When the magnetic field lines were parallel to the electric current, both the (111) and (220) textures were preferred in almost the same proportion. As a general conclusion of this work it can be said that by choosing the right experimental condition, one can improve the morphology and the properties of the deposited layers by applying a magnetic field. At the same time, the mass transport processes can be influenced by a magnetic field.

Tars have been identified as one of the major impurities associated with the utilization of biomass gasification fuel gas. Tars may result in blockages, plugging, corrosion and catalyst deactivation, leading to serious operational and maintenance problems during biomass gasification. Therefore, tar removal is essential to insure economic and effective fuel gas utilization. This study investigates the catalytic activity of zeolites, and nickel-supported zeolites for tar removal. Tests were conducted using a bench scale reactor and naphthalene as a model tar compound. Zeolites with varying pore sizes and acidity were tested to evaluate the effect of pore size and acidity on tar removal. Test results suggested that the catalytic activity increased with an increase in pore size and the number of acidic sites on the zeolite. The steam reforming ability of nickel towards naphthalene removal was evaluated by impregnating nickel on zeolites; this impregnation improved the activity of the catalysts significantly. Long term catalytic activity tests were performed, which showed that nickel supported ZY-30 and ZY-80 had the best naphthalene conversion, with naphthalene conversions of greater than 99%, followed by nickel- supported ZY-5.2, SiO2/Al2O3, and chabazite, respectively. This study also evaluated the catalytic activity of montmorillonite and nickel- supported montmorillonite as tar removal catalysts. Montmorillonite, and Ni-montmorillonite were tested for their efficiency in reforming tars. Also, the efficacy of nickel-supported montmorillonite catalyst was tested as a function of nickel content, reaction temperature, naphthalene loading, and the steam to carbon ratio. The results demonstrated that montmorillonite was catalytically active in removing naphthalene. In addition, Ni-montmorillonite had very high activity towards naphthalene removal via steam reforming, with removal efficiencies of greater than 99%. The activation energy was calculated for Ni-montmorillonite assuming first order kinetics and was found to be 84.5 kJ/mole. Long-term activity tests showed that the catalyst was active with naphthalene removal efficiencies of greater than 95%, which were maintained over a 97-hour test period. Very little loss of activity was observed with a drop in removal from 97 to 95%. The drop in catalytic activity was attributed primarily to a decrease in catalyst surface area, nickel sintering, and coke formation.

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