This master thesis is focused on producing orthopaedic implant materials and measuring their corrosion properties. It describes the bone and its structure, types, bone ossification and healing. It defines functions of orthopaedic implants and mentions the types of implants – biodegradable and non-biodegradable. The thesis interprets what corrosion is, what categories of corrosion exist and how does the corrosion influence orthopaedic implants. Preparing the solution of stimulated body fluid and manufacturing samples of different metal combinations (of iron, manganese, phosphorus, magnesium, silver and zinc) is included in this thesis, together with corrosion measurements, microscopic observations, EDAX analysis, metallographic analysis, microhardness testing of samples and pH changes measurements of solutions, and the results are interpreted and explained.

Concrete is a popular construction material for bridges, due to its high durability and energy efficiency. An important concern for concrete bridges is the possible occurrence of chloride- induced corrosion in prestressing strands and reinforcing bars, which may substantially impact the service life of such structures. Chloride- induced corrosion is a complicated electrochemical process which is affected by heat transfer, moisture flow and transport of chemical species through the concrete pore network. Reliable and robust analytical tools are required to allow multi-physics simulations of steel corrosion. This study has developed a nonlinear finite element analysis program, called VT-MultiPhys, to enable multi-physics simulations, including analyses of chloride-induced corrosion. The program includes constitutive laws, element formulations and global solution schemes to allow the analysis of steady-state (static) and time-dependent (dynamic) problems, involving multiple, coupled processes such as mechanical deformation, heat transfer, mass flow and chemical reactions combined with advective/diffusive transport of the various species. Special analysis schemes, based on the streamline-upwind Petrov-Galerkin (SUPG) method, have also been implemented to address the spatial instabilities which characterize analyses of advection-dominated transport. The finite element modeling scheme, constitutive laws and boundary conditions for analysis of chloride-induced corrosion are described in detail. The constitutive laws can be combined with inelastic material models to capture the damage (e.g., cracking) due to chloride-induced corrosion. A set of verification analyses is presented, to demonstrate the capabilities of VT-MultiPhys to conduct different types of simulations and reproduce the closed-form analytical solutions of simple cases. Validation analyses for heat conduction, moisture flow and chloride transport, using data from experimental tests in the literature, are also presented. / Master of Science / The deterioration of concrete structures and infrastructures due to the chloride-induced corrosion in prestressing strands and reinforcing bars may substantially impact the service life of such structures. Chloride-induced corrosion is a complicated electrochemical process which is initiated and proceeds due to the chloride attacks at the surfaces of concrete structures and ends in the volume expansion, cracking and spalling of concrete. Due to the lack of comprehensive modeling tool, which can simultaneously comprise the influential factors in chloride-induced corrosion, the realistic estimation of the service life of reinforced concrete structures is still challenging. Reliable and robust analytical tools are required to allow multi-physics simulations of steel corrosion. This study has developed a comprehensive finite element analysis program, called VT-MultiPhys, for calculating and monitoring the contribution of chloride ions to chloride-induced corrosion during service life of concrete structures. The present analysis program enables modeling of the coupled physical process including heat transfer, moisture flow and transport of chemical species through the concrete pore network. Also, by modeling the influence of flexural cracks on chloride transport in concrete, the analysis program is able to predict the rate of steel corrosion in cracked concrete structures. A set of verification analyses is presented, to demonstrate the capabilities of VT-MultiPhys to conduct different types of simulations of heat conduction, moisture flow and chloride transport and the comparison is found to be satisfactory. The element formulations and solution algorithms in VT-MultiPhys also allow the investigation of other long-term deterioration mechanisms, such as carbonation-induced corrosion, alkali-silika reaction (ASR) and sulfate attack. The present contribution will hopefully enable and facilitate future research in these topics, through the formulation and implementation of proper constitutive laws and chemical reaction equations.

No description available.

The pressure on clean and sustainable energy supplies is increasing. In this regard energy conversion by electrochemical processes plays a major role, for both fuel cell reactions and electrolysis reactions. The sulphur dioxide oxidation reaction (SOR) is a common reaction found in the Hybrid Sulphur Cycle (HyS) and the HyS is a way to produce large-scale hydrogen (H2). The problem with the use of the HyS and fuel cells is the cost involved as large amounts of Pt are required for effective operation. The aim of the study was to determine whether there was an alternative catalyst which was more efficient and cost-effective than Pt. The oxygen reduction reaction (ORR), the ethanol oxidation reaction (EOR) and SOR were studied by means of different electrochemical techniques (cyclovoltammetry (CV), linear polarization (LP) and rotating disk electrode (RDE)) on polycrystalline platinum (Pt) and palladium (Pd). The SRR and EOR are common reactions occurring at the cathode and anode, respectively, in fuel cells and these reactions have been investigated extensively. The reason for studying the reactions was as a preparation for the SOR. This study compared polycrystalline Pt and Pd for the different reactions, with the main focus on the SOR as Pd is considerably cheaper than Pt, and for the SOR polycrystalline Pd has by no means been investigated intensively. Polycrystalline Pt and Pd were compared by different electrochemical techniques and analyses. The Koutecky-Levich and Levich analyses were used to (i) calculate the number of e- involved in the relevant reaction, (ii) to determine whether the reaction was mass transfer controlled at high overpotentials and (iii) whether the reaction mechanism changed with potential. Next the kinetic current density ( k) was calculated from Koutecky-Levich analyses, which was further used for Tafel slope analyses. If it was not possible to carry out the analyses, the activation energy (Ea) was used to determine the electrocatalytic activity of the catalyst. The electrocatalytic activity was also determined by comparing onset potentials (Es), peak potentials (Ep) and limited/maximum current density ( b/ p) of each catalyst. This study was only a preliminary study for the SOR and therefore, further studies are certainly required. It seemed Pd shows better electrocatalytic activity than Pt for the SRR in an alkaline electrolyte because of similar Es, but Pd produced a higher cathodic current density. Pt showed a lower Es than Pd for the SRR in an acid electrolyte, but Pd delivered a higher cathodic current density. This, therefore, means that the SRR in an acid electrolyte is kinetically more favourable on Pd than on Pt. For the EOR better electrocatalytic activity was obtained with Pd than with Pt in an alkaline electrolyte due to higher current densities at lower potentials and Pd showed lower Ea values than Pt in the potential range normally used for fuel cells. Pd was inactive for EOR in an acid electrolyte, while a reaction occurred on Pt. A possible reason for this observation may be due to the H2 absorbing strongly on Pd thus blocking the active positions on the electrode surfaces, preventing further reaction. Pd showed higher electrocatalytic activity for the SOR due to lower Es and higher current densities at low potentials. From the RDE studies it was established that the SRR in an alkaline electrolyte on polycrystalline Pt and Pd was mass transfer controlled at low potentials (high overpotentials), but the SRR in an acid electrolyte was only mass transfer controlled on Pt. The SOR was not mass transfer controlled on polycrystalline Pt and Pd at high potentials (high overpotentials). These assumptions were confirmed by Levich analysis. Using Koutecky-Levich analysis, it was determined that the reaction mechanism on polycrystalline Pt and Pd changed with potential for SRR in an alkaline electrolyte and the SOR. For the SRR in an acid electrolyte the reaction mechanism remained constant with changes in potential on polycrystalline Pd, but the reaction mechanism on polycrystalline Pt changed with potential. These assumptions were confirmed by the number of e-, calculated using Koutecky-Levich analyses. Levich and Koutecky-Levich analyses were not performed for EOR as an increase in rotation speed did not produce an increase in current density. Tafel slope analyses were conducted by making use of overpotentials and k, where possible. As in the case of ethanol, it was not possible to execute Koutecky-Levich analyses and, therefore, it was not possible to perform Tafel slope analyses using k. Tafel slope analyses for the EOR was therefore performed with normal current densities at 0 rotations per minute (rpm). The reaction mechanisms on Pt and Pd for the SRR in alkaline and acidic electrolytes differed due to different Tafel slopes. Pt and Pd displayed similar Tafel slopes for the EOR in alkaline electrolyte, thus suggesting that the reaction mechanisms on Pt and Pd were the same. For the SOR it seemed that the reaction mechanism on Pt and Pd were similar because of similar Tafel slopes. This was only a preliminary and comparative study for polycrystalline Pt and Pd, and the reaction mechanism was not further studied by means of spectroscopic techniques. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

The pressure on clean and sustainable energy supplies is increasing. In this regard energy conversion by electrochemical processes plays a major role, for both fuel cell reactions and electrolysis reactions. The sulphur dioxide oxidation reaction (SOR) is a common reaction found in the Hybrid Sulphur Cycle (HyS) and the HyS is a way to produce large-scale hydrogen (H2). The problem with the use of the HyS and fuel cells is the cost involved as large amounts of Pt are required for effective operation. The aim of the study was to determine whether there was an alternative catalyst which was more efficient and cost-effective than Pt. The oxygen reduction reaction (ORR), the ethanol oxidation reaction (EOR) and SOR were studied by means of different electrochemical techniques (cyclovoltammetry (CV), linear polarization (LP) and rotating disk electrode (RDE)) on polycrystalline platinum (Pt) and palladium (Pd). The SRR and EOR are common reactions occurring at the cathode and anode, respectively, in fuel cells and these reactions have been investigated extensively. The reason for studying the reactions was as a preparation for the SOR. This study compared polycrystalline Pt and Pd for the different reactions, with the main focus on the SOR as Pd is considerably cheaper than Pt, and for the SOR polycrystalline Pd has by no means been investigated intensively. Polycrystalline Pt and Pd were compared by different electrochemical techniques and analyses. The Koutecky-Levich and Levich analyses were used to (i) calculate the number of e- involved in the relevant reaction, (ii) to determine whether the reaction was mass transfer controlled at high overpotentials and (iii) whether the reaction mechanism changed with potential. Next the kinetic current density ( k) was calculated from Koutecky-Levich analyses, which was further used for Tafel slope analyses. If it was not possible to carry out the analyses, the activation energy (Ea) was used to determine the electrocatalytic activity of the catalyst. The electrocatalytic activity was also determined by comparing onset potentials (Es), peak potentials (Ep) and limited/maximum current density ( b/ p) of each catalyst. This study was only a preliminary study for the SOR and therefore, further studies are certainly required. It seemed Pd shows better electrocatalytic activity than Pt for the SRR in an alkaline electrolyte because of similar Es, but Pd produced a higher cathodic current density. Pt showed a lower Es than Pd for the SRR in an acid electrolyte, but Pd delivered a higher cathodic current density. This, therefore, means that the SRR in an acid electrolyte is kinetically more favourable on Pd than on Pt. For the EOR better electrocatalytic activity was obtained with Pd than with Pt in an alkaline electrolyte due to higher current densities at lower potentials and Pd showed lower Ea values than Pt in the potential range normally used for fuel cells. Pd was inactive for EOR in an acid electrolyte, while a reaction occurred on Pt. A possible reason for this observation may be due to the H2 absorbing strongly on Pd thus blocking the active positions on the electrode surfaces, preventing further reaction. Pd showed higher electrocatalytic activity for the SOR due to lower Es and higher current densities at low potentials. From the RDE studies it was established that the SRR in an alkaline electrolyte on polycrystalline Pt and Pd was mass transfer controlled at low potentials (high overpotentials), but the SRR in an acid electrolyte was only mass transfer controlled on Pt. The SOR was not mass transfer controlled on polycrystalline Pt and Pd at high potentials (high overpotentials). These assumptions were confirmed by Levich analysis. Using Koutecky-Levich analysis, it was determined that the reaction mechanism on polycrystalline Pt and Pd changed with potential for SRR in an alkaline electrolyte and the SOR. For the SRR in an acid electrolyte the reaction mechanism remained constant with changes in potential on polycrystalline Pd, but the reaction mechanism on polycrystalline Pt changed with potential. These assumptions were confirmed by the number of e-, calculated using Koutecky-Levich analyses. Levich and Koutecky-Levich analyses were not performed for EOR as an increase in rotation speed did not produce an increase in current density. Tafel slope analyses were conducted by making use of overpotentials and k, where possible. As in the case of ethanol, it was not possible to execute Koutecky-Levich analyses and, therefore, it was not possible to perform Tafel slope analyses using k. Tafel slope analyses for the EOR was therefore performed with normal current densities at 0 rotations per minute (rpm). The reaction mechanisms on Pt and Pd for the SRR in alkaline and acidic electrolytes differed due to different Tafel slopes. Pt and Pd displayed similar Tafel slopes for the EOR in alkaline electrolyte, thus suggesting that the reaction mechanisms on Pt and Pd were the same. For the SOR it seemed that the reaction mechanism on Pt and Pd were similar because of similar Tafel slopes. This was only a preliminary and comparative study for polycrystalline Pt and Pd, and the reaction mechanism was not further studied by means of spectroscopic techniques. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

No description available.

This thesis primarily focuses on the electrochemical properties of the H₂/H⁺ redox couple, at various metallic electrodes in room temperature ionic liquids. Initially, a comprehensive overview of room temperature ionic liquids, RTILs, compared to conventional organic solvents is presented which identifies their favourable properties and applications, followed by a second chapter describing the basic theory of electrochemistry. A third chapter presents the general experimental reagents, instruments and measurements used in this thesis. The results presented in this thesis are summarized in six further chapters and shown as follows. (1) Hydrogenolysis, hydrogen loaded palladium electrodes by electrolysis of H[NTf₂] in a RTIL [C₂mim][NTf₂]. (2) Palladium nanoparticle-modified carbon nanotubes for electrochemical hydrogenolysis in RTILs. (3) Electrochemistry of hydrogen in the RTIL [C₂mim][NTf₂]: dissolved hydrogen lubricates diffusional transport. (4) The hydrogen evolution reaction in a room temperature ionic liquid: mechanism and electrocatalyst trends. (5) The formal potentials and electrode kinetics of the proton_hydrogen couple in various room temperature ionic liquids. (6) The electroreduction of benzoic acid: voltammetric observation of adsorbed hydrogen at a Platinum microelectrode in room temperature ionic liquids. The first two studies show electrochemically formed adsorbed H atoms at a metallic Pt or Pd surface can be used for clean, efficient, safe electrochemical hydrogenolysis of organic compounds in RTIL media. The next study shows the physicochemical changes of RTIL properties, arising from dissolved hydrogen gas. The last three studies looked at the electrochemical properties of H₂/H⁺ redox couple at various metallic electrodes over a range of RTILs vs a stable Ag/Ag⁺ reference couple, using H[NTf₂] and benzoic acid as proton sources. The kinetic and thermodynamic mechanisms of some reactions or processes are the same in RTILs as in conventional organic or aqueous solvents, but other remarkably different behaviours are presented. Most importantly significant constants are seen for platinum, gold and molybdenum electrodes in term of the mechanism of proton reduction to form hydrogen.

Master's thesis deals with new methods of preparing catalytic materials for positive electrode of an oxygen-hydrogen fuel cell and the influence of potassium permanganate or doping agent molar mass change on theirs attributes. Further it studies the use of proper measuring methods designed to qualify theirs attributes and the presentation of achieved results. In particular methods of linear sweep and cyclic voltammetry and the processing of data using Koutecky-Levich and Tafel plot and wave log analysis. Values of half-wave and onset potential and kinetic coefficient have been measured and calculated.

This work reports on the cobalt pyridinoporphyrazinate (CoTmtppa) as a platinum-group metal-free catalyst for hydrogen evolution and oxidation reactions with the possibility of use in hydrogen energy and hydrogen potentiometric sensing. A different interaction of CoTmtppa with various electrode substrates, highly oriented pyrolytic graphite (HOPG) and annealed gold (Au(111)), affects its electrocatalytic behaviour in hydrogen reactions. The formation of a hydride-type complex with the bonding of hydrogen atoms to cobalt centre is supposed to be the rate-determining step. In the case of hydrogen evolution, the maximum catalytic activity of mediator was reached at pH = 11,0, when the HOPG/CoTmtppa showed overpotential decrease by 300 mV and an almost 60-fold increase of current densities compared to HOPG. The electrocatalytic activity of Au(111)/CoTmtppa resulted in a further decrease of overpotential by 175 mV in comparison with HOPG/Co(I)Tmtppa. The electrochemical oxidation of hydrogen was found to depend on hydrogen source which was electrochemically generated on-site or molecular hydrogen supplied from an external source. In the case of electrochemically generated hydrogen, the maximum activity of HOPG/CoTmtppa was reached at pH = 2.1 and an additional it was observed 50 % increase in current...