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For patients suffering bradycardia, i.e., too slow heart rhythm, the common treatment is having a pacemaker implanted. The pacemaker system consists of the pacemaker and a pacing lead. The pacing lead is connected to the pacemaker and at the other end there is a stimulation electrode. The most common conductor material is a cobalt-based super alloy (MP35N® or 35N LT®), with the main constituents Ni, Co, Cr and Mo. The pacemaker electrode is often made of a substrate material with a rough surface coating. The substrate materials are predominantly platinum/iridium alloy and titanium. The material choice is of great importance for the performance and stability during long-term service. Excellent corrosion resistance is required to minimize elution of metal ions in the human body. In this thesis, the electrochemical behaviour and corrosion resistance of the Co-based alloys and Ta (as electrode substrate), in a phosphate buffer saline (PBS) solution with and without addition of H2O2, was investigated by means of potentiodynamic polarization, cyclic voltammetry, electrochemical impedance spectroscopy and simulated pacemaker pulsing. The metal release from the Co-based alloy during the passivation treatment and exposure in the synthetic biological media was measured by using inductive coupled plasma - atomic emission spectroscopy (ICP-AES). Moreover, surface composition was analyzed by using x-ray photoelectron spectroscopy. The results show that the chemical passivation of Co-based alloy 35N LT® increased the corrosion resistance and reduced Co release significantly, even in more hostile environment, i.e. PBS with addition of H2O2. The increased corrosion resistance is due to the Cr enrichment in the surface layer. The reduced Co release is due to a preferential dissolution of Co from the surface oxide layer during the chemical passivation. The electrochemical investigation of uncoated and rough TiN coated Ta show that uncoated Ta is not suitable electrode material due to formation of a highly resistive surface oxide film. Whereas the rough TiN coated Ta exhibits desirable electrochemical performance for pacemaker electrodes. The addition of H2O2 in the PBS has a large influence on the electrochemical behaviour of Ta, but the influence is small on the rough TiN coated Ta. / QC 20101122

Yes / In this study, anti-corrosion concrete for sewage system was developed with nano TiO2 (NT) and reactive powder concrete (RPC). The corrosion resistances of NT modified RPC (NTMRPC) in high concentration enhanced sewage were investigated from the perspectives of biological, physical and chemical corrosion resistances, respectively. In addition, mechanical properties of NTMRPC after sewage corrosion were also studied. Research results indicated that NT can endow RPC with antimicrobial property through their microorganism biodegradation properties. The inhibition and elimination rates of NTMRPC to its surface microorganisms were 37.35% and 80.93%, respectively. After sewage corrosion, the surface roughness, mass loss and deterioration depth of RPC were decreased by 62.57%, 15.48% and 18.44% due to the NT inclusion, respectively. In addition, the pH values of RPC in the deterioration depth ranges of 0-3 mm and 3-6 mm were increased by 11.45% and 23.62%, respectively. NT can restrain the strength deterioration of RPC in high concentration enhanced sewage. This may be due to the improved sewage biological anti-corrosion performances of RPC by inhibiting/eliminating the microorganisms on the surface of RPC as well as the enhanced sewage physical/chemical anti-corrosion performances of RPC by improving the compactness of RPC. / The authors thank the funding provided by the National Science Foundation of China 513 (51978127 and 51908103), and National Key Research and Development Program of China 514 (2018YFC070560 and 2017YFC0703410).

Surface integrity of manufactured components has a critical impact on their functional performance. Magnesium alloys are lightweight materials used in the transportation industry and are also emerging as a potential material for biodegradable medical implants. However, the unsatisfactory corrosion performance of Mg alloys limits their application to a great extent. Surface integrity factors, such as grain size, crystallographic orientation and residual stress, have been proved to remarkably influence the functional performance of magnesium alloys, including corrosion resistance, wear resistance and fatigue life. In this dissertation, the influence of machining conditions, including dry and cryogenic cooling (liquid nitrogen was sprayed to the machined surface during machining), cutting edge radius, cutting speed and feed rate, on the surface integrity of AZ31B Mg alloy was investigated. Cryogenic machining led to the formation of a "featureless layer" on the machined surface where significant grain refinement from 12 μm to 31 nm occurred due to dynamic recrystallization (DRX), as well as increased intensity of basal plane on the surface and more compressive residual stresses. Dry and cryogenic burnishing experiments of the same material were conducted using a fixed roller setup. The thickness of the processed-influenced layer, where remarkable microstructural changes occurred, was dramatically increased from the maximum value of 20 μm during machining to 3.4 mm during burnishing. The burnishing process also produced a stronger basal texture on the surface than the machining process. Preliminary corrosion tests were conducted to evaluate the corrosion performance of selected machined and burnished AZ31B Mg samples in 5% NaCl solution and simulated body fluid (SBF). Cryogenic cooling and large edge radius tools were found to significantly improve the corrosion performance of machined samples in both solutions. The largest improvement in the material's corrosion performance was achieved by burnishing. A finite element study was conducted for machining of AZ31B Mg alloy and calibrated using the experimental data. A user subroutine was developed and incorporated to predict the grain size changes induced by machining. Good agreements between the predicted and measured grain size as well as thickness of featureless layers were achieved. Numerical studies were extended to include the influence of rake angle, feed rate and cutting speed on the featureless layer formation.

The optimal conditions for deposition of zinc-nickel alloys onto stainless steel discs in alkaline solutions have been examined. In the past cadmium has been used because it shows good corrosion protection, but other methods are being examined due to the high toxicity and environmental threats posed by its use. Zinc has been found to provide good corrosion resistance, but the corrosion resistance is greatly increased when alloyed with nickel. The concentration of nickel in the deposit has long been a debated issue, but for basic solutions a nickel concentration of 8-15% appears optimal. However, deposition of zinc-nickel alloys from acidic solutions has average nickel concentrations of 12-15%. Alkaline conditions give a more uniform deposition layer, or better metal distribution, thereby a better corrosion resistance. Although TEA (triethanolamine) is most commonly used to complex the metals in solution, in this work I examined TEA along with other complexing agents. Although alkaline solutions have been examined, most research has been done in pH ≥ 12 solutions. However, there has been some work performed in the pH 9.3-9.5 range. This work examines different ligands in a pH 9.3-9.4 range. Direct potential plating and pulse potential plating methods are examined for optimal platings. The deposits were examined and characterized by XRD.

soldagem de aços inoxidáveis duplex AID SAF 2205 utilizando o processo Metal Active Gas (MAG) ainda tem poucos dados e referências, estes aços são conceituados devido ao seu equilíbrio entre resistência mecânica e à corrosão, resultado de sua microestrutura composta por austenita e ferrita. A soldagem dos aços inoxidáveis duplex exige um controle de aporte térmico, da composição química do metal de adição e gás de proteção. Mínimas mudanças em parâmetros e composição dos consumíveis podem afetar diretamente a estrutura formada na região da solda. Neste trabalho, o objetivo foi estudar a influência da utilização do processo de soldagem MAG com diferentes energias aplicadas ao AID SAF 2205, sobre a resistência à corrosão das amostras resultantes. Foram usados quatro valores de energias de soldagem, entre 0,6 e 1,1 kJ/mm, sendo a maior energia limitada à espessura das chapas, que era de 5 mm. Quando foi analisada a microestrutura formada na região da solda, a quantificação de ferrita na zona afetada pelo calor apresentou uniformidade nas amostras, independendo da energia de soldagem. Contudo, a quantidade de ferrita no metal de solda diminuiu à medida que a energia aumentou. A precipitação de nitretos de cromo foi observada no interior de alguns grãos de ferrita e/ou próximo a regiões com austenita secundária intragranular. Os perfis de microdureza Vickers não apresentaram nenhum valor acima de 300 HV, e nenhum comportamento diferenciado de acordo com área de indentação. A resistência à corrosão não apresentou mudanças consideráveis, o metal base e as regiões da solda nas quatro condições se comportaram de forma muito similar. Os ensaios de imersão em cloreto férrico, seguindo a ASTM G48, permitiram observar a formação de pites, mas a quantidade e densidade destes não pode ser associada a uma região da solda específica ou variação de energia de soldagem. Os valores de parâmetros eletroquímicos, OCP, ECORR, e EPIT, após os ensaios de polarização potenciodinâmica de acordo com a ASTM G5, tiveram pouca variação, mostrando um comportamento em corrosão similar para o metal base e para os metais de solda das quatro diferentes condições de energia de soldagem empregadas. / Welding of AID SAF 2205 duplex stainless steels using the Metal Active Gas (MAG) process still has few data and references, these steels are conceptualized due to their balance between mechanical resistance and corrosion, resulting from their microstructure composed of austenite and ferrite. The welding of duplex stainless steels requires a control of the thermal input, the chemical composition of the addition metal and the shielding gas. Minimal changes in parameters and composition of consumables will directly affect the structure formed in the region of the weld. In this work, the objective was to study the influence of the MAG welding process with different energies applied to AID SAF 2205, on the corrosion resistance of the resulting samples. Four values of welding energies were used, between 0.6 and 1.1 kJ / mm, with the greatest energy limited to the thickness of the plates, which was 5 mm. When the microstructure formed in the region of the weld was analyzed, the quantification of ferrite in the zone affected by the heat showed uniformity in the samples, independent of the welding energy. However, the amount of ferrite in the weld metal decreased as the energy increased. The precipitation of chromium nitrides was observed in the intermetallic was associated with grain boundaries α / γ, inside some ferrite grains, close to regions with secondary intragranular austenite. The Vickers microhardness profiles showed no value above 300 HV, and no behavior differed according to the indentation area. The corrosion resistance did not change considerably, the base metal and the regions of the weld in the four conditions behaved very similarly. Ferric chloride immersion assays, following ASTM G48, allowed to observe the formation of pites, but the amount and density thereof can not be associated with a specific weld region or weld energy variation. The values of electrochemical parameters, OCP, ECORR, and EPIT, after the potentiodynamic polarization tests according to ASTM G5, showed little variation, showing a similar corrosion behavior for the base metal and the solder metals of the four Different welding energy conditions employed.

In order to meet the need of metallurgical industry in the world, a new MgAlON-BN composite which can be used for example in special refractory nozzles, tubes and break rings for the continuous casting of steel was studied in the present thesis. The aim was to understand the mechanism of synthesis and their physicochemical properties during the application. Thus, the thermodynamic properties, synthesis process, mechanical properties, thermal shock behaviour, thermal diffusivity/conductivity as well as corrosion resistance to molten iron containing oxygen and molten slag of MgAlON and MgAlON-BN composites have been investigated. The Gibbs energy of formation of MgAlON was estimated using the method proposed by Kaufman. The phase stability diagram of Mg-Al-O-N-B was investigated, and consequently the synthesis parameters were determined. MgAlON and MgAlON-BN composites were fabricated by hot-pressing method. The composites obtained this way were characterized by XRD, SEM, TEM and HREM analyses. A Matrix-flushing method was employed in the quantitative XRD analysis for the multi-component samples to understand the mechanism of synthesis. The relationship between mechanical properties and microstructure of the composites was investigated. The experimental results indicated that BN addition has significant influence on the mechanical properties of the composites. These can be explained by the fact that BN has low Young’s modulus, density and non-reactive nature as well as considerable anisotropy of many properties such as thermal expansion, thermal diffusivity/conductivity. Thus, the addition of BN in MgAlON is likely to lead to the presence of microcracks caused by the mismatch of thermal expansion coefficient. The microcracks result in the enhancement of the strength at elevated temperature and thermal shock durability of the composites. Effective thermal conductivities were evaluated from the present experimental results of thermal diffusivities, heat capacity and density. A model suitable for present composites has been derived based on Luo’s model. The predicted lines calculated by the model were in good agreement with experimental results. The reactions between the composites and molten iron as well as the slag were investigated by ‘‘finger’’ experiments and sessile drop experiments. Both experimental results indicated that the BN addition has positive influence on the corrosion resistance. These are attributed to the excellent corrosion resistance of BN to molten iron and slag, such as the higher contact angle between BN substrate and liquid iron and molten slag compared with that obtained for pure MgAlON. / QC 20100929

The aim of this research proj ect was to produce compositionally modulated zincnickel and zinc-nickel-manganese coatings usi ng a single bath process by variation of the applied electroplating current density. These could then be considered as possible replacements for electroplated cadmium. Zinc-nickel electrodeposits from both a simple bath and one containing the complexant tris(hydroxymethyl)methylamine (TRIS) were produced using either bath or by selective electroplating onto mild steel, 2014-T6 aluminium and 2000 series aluminium alloy connector shells. Zinc-nickelmanganese coatings were electroplated onto mild steel, using both DC and pulse electroplating from sulphate based baths containing either the complexant TRIS or sodium citrate. The coatings and the various electrodeposition processes were evaluated by thickness measurements, cun'ent efficiency calculations, composition detennination using energy dispersive X-ray anal ys is and SEM to examine the morphology. Corrosion characteristics were investigated by neutral salt fog exposure, alternate immersion, atmospheric trials, and electrochemical immersion tests including potential monitoring, galvanic and polarisation measurements. Other properties such as microhardness and surface electrical conductivity were also investigated. Compositionally modulated zinc-nickel and ziJlc-nickel-manganese were successfully deposited from single baths with nickel contents ranging from 5-20% Ni and manganese contents varying from 0-12% Mn. Current efficiency measurements showed the efficiency to be low especially for the zinc-nickel-manganese coatings, which exhibited a distinct morphology when electroplated from the citrate bath. Corrosion testing indicated that both coatings had a lower corrosion resistance than cadmium especially in accelerated tests, with a reduction in corrosion resistance being seen as the nickel content was increased; due to a decrease in density of the electroplate. This, and increasing through-thickness porosity promoted ennoblement of zinc-nickel and zinc-nickel-manganese leading to the coatings becoming nonsacri ficial to the substrate in accelerated tests. Zinc-nickel-manganese showed less white rust than zinc-nickel and exhibited lligher micro-hardness than zinc, cadmium and zinc-nickel. Electrical measurements indicated that both coatings were sufficiently conductive to meet the surface conductivity requirements for use on electrical connector shells.