Biomateriais metálicos devem apresentar uma combinação de propriedades como resistência à corrosão, biocompatibilidade e resistência mecânica. Os aços inoxidáveis austeníticos, especialmente do tipo AISI 316L, aliam estas propriedades com a possibilidade de fabricação a um baixo custo. No entanto, são susceptíveis à corrosão nos fluidos fisiológicos e seus produtos de corrosão podem causar reações alérgicas ou infecciosas nos tecidos vizinhos ao implante. No presente trabalho, a aplicação de revestimentos obtidos por processos de deposição física de vapor (PVD) sobre um aço inoxidável austenítico do tipo AISI 316L foi realizada a fim de aumentar sua resistência à corrosão e biocompatibilidade. Os filmes depositados foram de nitreto de titânio (TiN), carbonitreto de titânio (TiCN) e de carbono tipo diamante (DLC). Estes materiais têm alta dureza e resistência ao desgaste, além de biocompatibilidade intrínseca, características altamente desejáveis para aplicações biomédicas. A caracterização do comportamento eletroquímico do aço com os três tipos de revestimentos mostrou que a presença de defeitos na superfície das camadas depositadas exerce uma influência negativa sobre a resistência à corrosão do substrato. A presença dos defeitos foi evidenciada por microscopia eletrônica de varredura. Foi proposto um mecanismo, com base nos dados obtidos por espectroscopia de impedância eletroquímica, para explicar a evolução do comportamento eletroquímico do aço com os diferentes revestimentos ao longo do tempo de imersão. Foram também empregados dois tratamentos de passivação da superfície do aço em soluções de ácido sulfúrico e ácido nítrico, a fim de aumentar a resistência à corrosão do substrato. Os resultados indicaram que os tratamentos utilizados não foram eficientes para melhorar esta característica, mas podem ser modificados visando um desempenho superior. As propriedades eletrônicas dos filmes passivos formados, tanto sobre o aço sem tratamento de passivação como sobre o aço passivado, foram estudadas utilizando a abordagem de Mott-Schottky. Os filmes apresentaram um caráter duplex, mostrando comportamento de um semicondutor altamente dopado acima e abaixo do potencial de banda plana. A concentração de dopantes no filme passivo foi associada à resistência à corrosão do material. Os três revestimentos PVD investigados apresentaram comportamento não citotóxico. Considerando a diminuição do coeficiente de atrito do aço 316L, os revestimentos de TiCN e o DLC foram os mais eficientes. Estas características, aliadas ao fator custo, sugerem que a aplicação comercial destes materiais sobre implantes ortopédicos pode ser viável. No entanto, a resistência à corrosão, conforme a avaliação realizada no presente estudo, não foi adequada quando comparada ao desempenho do aço sem nenhum tipo de revestimento. Ao final do texto, são apresentadas algumas sugestões a fim de conseguir um desempenho superior para a capacidade protetora dos revestimentos PVD. / Metallic biomaterials must present a combination of properties such as corrosion resistance, biocompatibility and mechanical resistance. Austenitic stainless steels, especially AISI 316L combine these properties with the easy of fabrication at low cost. However, they are prone to corrosion in physiological solutions. Furthermore, their corrosion products may lead to infectious ou allergenic reactions in the tissues around the implant device. In the present work, coatings produced by physical vapour deposition (PVD) methods have been applied on the surface of a 316L stainless steel to increase its corrosion resistance and biocompatibility. Three thin films were tested: titanium nitride (TiN), titanium carbonitride (TiCN) and diamond-like carbon (DLC). These materials present high hardness, wear resistance and intrinsic biocompatibility that are key features when considering biomedical applications. The characterization of the electrochemical behavior of the stainless steel coated with the three different films showed that the presence of surface defects are deleterious to the corrosion resistance of the substrate. These defects were observed using scanning electron microscopy. The evolution of the electrochemical behavior of the coated steel was explained through a mechanism based on the experimental results obtained using electrochemical impedance spectroscopy. Two different passivation treatments were carried out on the stainless steel surface, either in sulfuric or nitric acid solutions, to increase its corrosion resistance. The results suggested que these treatments were not efficient, but may be modified to improve its performance. The electronic properties of the passive films of the non-passivated and passivated stainless steel were studied using the Mott-Schottky approach. The films presented a duplex character. Below the flatband potential the behavior is typical of a highly doped type-p semiconductor. Above the flatband potential is typical of a highly doped type-n semiconductor. The doping concentration in the passive film was determined and associated with the corrosion resistance of the substrate. All PVD coatings investigated showed non-cytotoxic behavior. DLC and TiCN coatings decreased the friction coefficient of the stainless steel substrate. These properties allied with the stainless steel low cost recommend their commercial use for implants materials purposes. Nevertheless the corrosion resistance presented by the coated-steel was inferior to that of the bare steel and should be improved. At the end of the present text, some suggestions are proposed in order to improve the corrosion protection performance of the PVD coatings.

Biomateriais metálicos devem apresentar uma combinação de propriedades como resistência à corrosão, biocompatibilidade e resistência mecânica. Os aços inoxidáveis austeníticos, especialmente do tipo AISI 316L, aliam estas propriedades com a possibilidade de fabricação a um baixo custo. No entanto, são susceptíveis à corrosão nos fluidos fisiológicos e seus produtos de corrosão podem causar reações alérgicas ou infecciosas nos tecidos vizinhos ao implante. No presente trabalho, a aplicação de revestimentos obtidos por processos de deposição física de vapor (PVD) sobre um aço inoxidável austenítico do tipo AISI 316L foi realizada a fim de aumentar sua resistência à corrosão e biocompatibilidade. Os filmes depositados foram de nitreto de titânio (TiN), carbonitreto de titânio (TiCN) e de carbono tipo diamante (DLC). Estes materiais têm alta dureza e resistência ao desgaste, além de biocompatibilidade intrínseca, características altamente desejáveis para aplicações biomédicas. A caracterização do comportamento eletroquímico do aço com os três tipos de revestimentos mostrou que a presença de defeitos na superfície das camadas depositadas exerce uma influência negativa sobre a resistência à corrosão do substrato. A presença dos defeitos foi evidenciada por microscopia eletrônica de varredura. Foi proposto um mecanismo, com base nos dados obtidos por espectroscopia de impedância eletroquímica, para explicar a evolução do comportamento eletroquímico do aço com os diferentes revestimentos ao longo do tempo de imersão. Foram também empregados dois tratamentos de passivação da superfície do aço em soluções de ácido sulfúrico e ácido nítrico, a fim de aumentar a resistência à corrosão do substrato. Os resultados indicaram que os tratamentos utilizados não foram eficientes para melhorar esta característica, mas podem ser modificados visando um desempenho superior. As propriedades eletrônicas dos filmes passivos formados, tanto sobre o aço sem tratamento de passivação como sobre o aço passivado, foram estudadas utilizando a abordagem de Mott-Schottky. Os filmes apresentaram um caráter duplex, mostrando comportamento de um semicondutor altamente dopado acima e abaixo do potencial de banda plana. A concentração de dopantes no filme passivo foi associada à resistência à corrosão do material. Os três revestimentos PVD investigados apresentaram comportamento não citotóxico. Considerando a diminuição do coeficiente de atrito do aço 316L, os revestimentos de TiCN e o DLC foram os mais eficientes. Estas características, aliadas ao fator custo, sugerem que a aplicação comercial destes materiais sobre implantes ortopédicos pode ser viável. No entanto, a resistência à corrosão, conforme a avaliação realizada no presente estudo, não foi adequada quando comparada ao desempenho do aço sem nenhum tipo de revestimento. Ao final do texto, são apresentadas algumas sugestões a fim de conseguir um desempenho superior para a capacidade protetora dos revestimentos PVD. / Metallic biomaterials must present a combination of properties such as corrosion resistance, biocompatibility and mechanical resistance. Austenitic stainless steels, especially AISI 316L combine these properties with the easy of fabrication at low cost. However, they are prone to corrosion in physiological solutions. Furthermore, their corrosion products may lead to infectious ou allergenic reactions in the tissues around the implant device. In the present work, coatings produced by physical vapour deposition (PVD) methods have been applied on the surface of a 316L stainless steel to increase its corrosion resistance and biocompatibility. Three thin films were tested: titanium nitride (TiN), titanium carbonitride (TiCN) and diamond-like carbon (DLC). These materials present high hardness, wear resistance and intrinsic biocompatibility that are key features when considering biomedical applications. The characterization of the electrochemical behavior of the stainless steel coated with the three different films showed that the presence of surface defects are deleterious to the corrosion resistance of the substrate. These defects were observed using scanning electron microscopy. The evolution of the electrochemical behavior of the coated steel was explained through a mechanism based on the experimental results obtained using electrochemical impedance spectroscopy. Two different passivation treatments were carried out on the stainless steel surface, either in sulfuric or nitric acid solutions, to increase its corrosion resistance. The results suggested que these treatments were not efficient, but may be modified to improve its performance. The electronic properties of the passive films of the non-passivated and passivated stainless steel were studied using the Mott-Schottky approach. The films presented a duplex character. Below the flatband potential the behavior is typical of a highly doped type-p semiconductor. Above the flatband potential is typical of a highly doped type-n semiconductor. The doping concentration in the passive film was determined and associated with the corrosion resistance of the substrate. All PVD coatings investigated showed non-cytotoxic behavior. DLC and TiCN coatings decreased the friction coefficient of the stainless steel substrate. These properties allied with the stainless steel low cost recommend their commercial use for implants materials purposes. Nevertheless the corrosion resistance presented by the coated-steel was inferior to that of the bare steel and should be improved. At the end of the present text, some suggestions are proposed in order to improve the corrosion protection performance of the PVD coatings.

Hard coatings deposited by physical vapour deposition (PVD) are commonly used to improve the scratch resistance and hardness of objects made of softer materials such as steel, and they can also be used as decorative coatings since they exhibit a wide range of different colours. In this research, stainless steel tableware utensils were coated with multilayer Ti/TiCN thin films to give the tableware a wear-resistant decorative finish. A cathodic arc PVD system was used to deposit the coatings since it has the potential to produce very dense coatings with excellent adhesion and wear-resistance properties in relatively short deposition times. Several system parameters were varied between deposition cycles to create a large set of samples which included: changing the amount of flatware present inside of the chamber during deposition, changing the size of the flatware used, changing the mounting location of the flatware inside of the chamber, and changing the depletion level of the titanium cathode targets used to deposit titanium. It was found that changing these variables had an effect on the deposition rate of the coating and thus had an effect on the thickness of the titanium interlayer, which was found to be an important factor in achieving good adhesion of the TiCN layer. The optimal titanium interlayer thickness was found to be in the range of approximately 120 to 230 nm. / Thesis / Master of Applied Science (MASc)

As vantagens relacionadas à utilização de revestimentos duros depositados via processos PAPVD (Plasma Assisted Physical Vapor Deposition) são bem conhecidas e dadas por suas propriedades. As principais propriedades destes filmes são a capacidade de não incrementar significativamente a rugosidade dos substratos em que são depositados, sua alta dureza conferindo alta resistência ao desgaste, baixa reatividade quando se trata de revestimentos de compostos cerâmicos e capacidade de reduzir o coeficiente de atrito de pares tribológicos inseridos em diversos meios. A nitretação a plasma de substratos antes da aplicação de um revestimento faz com que outros benefícios possam ser encontrados, dentre eles destacam-se o aumento da capacidade de sustentação de carga do substrato e a criação de uma região que propicia um gradiente de propriedades entre o substrato e o revestimento. Desta forma é caracterizado o tratamento dúplex, o qual consiste em um substrato nitretado seguido da aplicação de um revestimento. Através do processo de nitretação a plasma, camadas de difusão foram formadas em amostras de geometria cilíndrica do aço DIN X100CrMoV8-1-1, industrialmente utilizado para construção de ferramentas para operações de corte e estampagem. Duas profundidades distintas de camada de difusão foram formadas. O revestimento escolhido para este estudo foi o TiCN (carbonitreto de titânio), produzido industrialmente e disponível no mercado brasileiro. As técnicas de caracterização foram utilizadas para medir a rugosidade, a dureza, os perfis de composição química, as fases formadas, as tensões residuais e a adesão dos revestimentos. Após esta caracterização inicial, foram feitos ensaios utilizando a técnica de esfera-sobre-disco em amostras e de DST (Dobramento sob Tensão) em pinos com geometria específica com o objetivo de se avaliar o comportamento tribológico dos tratamentos dúplex desenvolvidos. / The advantages related to the utilization of hard thin films deposited on tools and components via PAPVD (Plasma Assisted Physical Vapor Deposition) are well known and given by their properties. The main properties of these coatings are their capacity to avoid significant roughness increase of the coated substrates, high hardness which provides high wear resistance, low reactivity in the case of ceramic coatings and the possibility to provide very low friction coefficient. The thin films associated with plasma nitriding (the so called duplex treatments) applied to the substrates can bring much more benefits. The coating load bearing capacity can be increased by the presence of the diffusion zone on the substrate that allows a gradient of mechanical properties from the coating to the core of the material. In this work, by plasma nitriding process, two distinct depths of diffusion layer were developed in samples and pins manufactured out of the DIN X100CrMoV8-1-1 steel. This steel grade is commonly used to manufacture tools for cutting and stamping operations. Following a previous work the chosen coating for this study was a graded TiCN (titanium carbonitride). The samples were characterized by several different techniques in order to access surface roughness, chemical composition profiles, present phases, residual stresses, hardness and adhesion of the obtained nitrided layer and coatings. After this initial characterization, tests were performed using a pin-on-disc apparatus and BUT (Bending under tension test) with the aim to evaluate the tribological behavior of the developed duplex treatment for for sheet metal forming application.

As vantagens relacionadas à utilização de revestimentos duros depositados via processos PAPVD (Plasma Assisted Physical Vapor Deposition) são bem conhecidas e dadas por suas propriedades. As principais propriedades destes filmes são a capacidade de não incrementar significativamente a rugosidade dos substratos em que são depositados, sua alta dureza conferindo alta resistência ao desgaste, baixa reatividade quando se trata de revestimentos de compostos cerâmicos e capacidade de reduzir o coeficiente de atrito de pares tribológicos inseridos em diversos meios. A nitretação a plasma de substratos antes da aplicação de um revestimento faz com que outros benefícios possam ser encontrados, dentre eles destacam-se o aumento da capacidade de sustentação de carga do substrato e a criação de uma região que propicia um gradiente de propriedades entre o substrato e o revestimento. Desta forma é caracterizado o tratamento dúplex, o qual consiste em um substrato nitretado seguido da aplicação de um revestimento. Através do processo de nitretação a plasma, camadas de difusão foram formadas em amostras de geometria cilíndrica do aço DIN X100CrMoV8-1-1, industrialmente utilizado para construção de ferramentas para operações de corte e estampagem. Duas profundidades distintas de camada de difusão foram formadas. O revestimento escolhido para este estudo foi o TiCN (carbonitreto de titânio), produzido industrialmente e disponível no mercado brasileiro. As técnicas de caracterização foram utilizadas para medir a rugosidade, a dureza, os perfis de composição química, as fases formadas, as tensões residuais e a adesão dos revestimentos. Após esta caracterização inicial, foram feitos ensaios utilizando a técnica de esfera-sobre-disco em amostras e de DST (Dobramento sob Tensão) em pinos com geometria específica com o objetivo de se avaliar o comportamento tribológico dos tratamentos dúplex desenvolvidos. / The advantages related to the utilization of hard thin films deposited on tools and components via PAPVD (Plasma Assisted Physical Vapor Deposition) are well known and given by their properties. The main properties of these coatings are their capacity to avoid significant roughness increase of the coated substrates, high hardness which provides high wear resistance, low reactivity in the case of ceramic coatings and the possibility to provide very low friction coefficient. The thin films associated with plasma nitriding (the so called duplex treatments) applied to the substrates can bring much more benefits. The coating load bearing capacity can be increased by the presence of the diffusion zone on the substrate that allows a gradient of mechanical properties from the coating to the core of the material. In this work, by plasma nitriding process, two distinct depths of diffusion layer were developed in samples and pins manufactured out of the DIN X100CrMoV8-1-1 steel. This steel grade is commonly used to manufacture tools for cutting and stamping operations. Following a previous work the chosen coating for this study was a graded TiCN (titanium carbonitride). The samples were characterized by several different techniques in order to access surface roughness, chemical composition profiles, present phases, residual stresses, hardness and adhesion of the obtained nitrided layer and coatings. After this initial characterization, tests were performed using a pin-on-disc apparatus and BUT (Bending under tension test) with the aim to evaluate the tribological behavior of the developed duplex treatment for for sheet metal forming application.

As vantagens relacionadas à utilização de revestimentos duros depositados via processos PAPVD (Plasma Assisted Physical Vapor Deposition) são bem conhecidas e dadas por suas propriedades. As principais propriedades destes filmes são a capacidade de não incrementar significativamente a rugosidade dos substratos em que são depositados, sua alta dureza conferindo alta resistência ao desgaste, baixa reatividade quando se trata de revestimentos de compostos cerâmicos e capacidade de reduzir o coeficiente de atrito de pares tribológicos inseridos em diversos meios. A nitretação a plasma de substratos antes da aplicação de um revestimento faz com que outros benefícios possam ser encontrados, dentre eles destacam-se o aumento da capacidade de sustentação de carga do substrato e a criação de uma região que propicia um gradiente de propriedades entre o substrato e o revestimento. Desta forma é caracterizado o tratamento dúplex, o qual consiste em um substrato nitretado seguido da aplicação de um revestimento. Através do processo de nitretação a plasma, camadas de difusão foram formadas em amostras de geometria cilíndrica do aço DIN X100CrMoV8-1-1, industrialmente utilizado para construção de ferramentas para operações de corte e estampagem. Duas profundidades distintas de camada de difusão foram formadas. O revestimento escolhido para este estudo foi o TiCN (carbonitreto de titânio), produzido industrialmente e disponível no mercado brasileiro. As técnicas de caracterização foram utilizadas para medir a rugosidade, a dureza, os perfis de composição química, as fases formadas, as tensões residuais e a adesão dos revestimentos. Após esta caracterização inicial, foram feitos ensaios utilizando a técnica de esfera-sobre-disco em amostras e de DST (Dobramento sob Tensão) em pinos com geometria específica com o objetivo de se avaliar o comportamento tribológico dos tratamentos dúplex desenvolvidos. / The advantages related to the utilization of hard thin films deposited on tools and components via PAPVD (Plasma Assisted Physical Vapor Deposition) are well known and given by their properties. The main properties of these coatings are their capacity to avoid significant roughness increase of the coated substrates, high hardness which provides high wear resistance, low reactivity in the case of ceramic coatings and the possibility to provide very low friction coefficient. The thin films associated with plasma nitriding (the so called duplex treatments) applied to the substrates can bring much more benefits. The coating load bearing capacity can be increased by the presence of the diffusion zone on the substrate that allows a gradient of mechanical properties from the coating to the core of the material. In this work, by plasma nitriding process, two distinct depths of diffusion layer were developed in samples and pins manufactured out of the DIN X100CrMoV8-1-1 steel. This steel grade is commonly used to manufacture tools for cutting and stamping operations. Following a previous work the chosen coating for this study was a graded TiCN (titanium carbonitride). The samples were characterized by several different techniques in order to access surface roughness, chemical composition profiles, present phases, residual stresses, hardness and adhesion of the obtained nitrided layer and coatings. After this initial characterization, tests were performed using a pin-on-disc apparatus and BUT (Bending under tension test) with the aim to evaluate the tribological behavior of the developed duplex treatment for for sheet metal forming application.

Titanium alloys are major materials used in the airplane industry, and prospects show that airplane production will double in the next 20 years. Consequently, the demand for cutting tools for machining of titanium alloys will increase. The primary problem when machining titanium alloys is their low thermal conductivity. Crater wear is the main factor limiting tool life, and is generally caused by thermal diffusion due to high temperatures in the tool-chip interface. This master’s thesis was performed in collaboration with Sandvik Coromant, with the prospect to increase knowledge of how diffusion and chip formation influences crater wear progression. The aim was to study tool wear of cutting tools when turning Ti–6Al–4V. This was done by testing two different rake face geometries, both coated and uncoated, at cutting speeds of 30–115 m/min. Diffusion was investigated to learn about the impact it has on crater wear. Chips were examined to investigate chip formation and shear strain. The coated modified rake face insert showed less crater wear only for the initial few seconds of machining. Uncoated inserts with a modified rake face showed higher diffusion rate and faster crater wear progression than did standard inserts. The standard inserts showed twice as long tool life as did the modified inserts. No significant differences in the chip formation mechanism were found between modified and standard inserts. Cracks were found within shear bands that were thinner than usual, which suggest that the generation of cracks allows less shear deformation.

Cutting tools are subject to extreme environment during processing, with hightemperatures and pressures. CVD coatings are used to increase lifetime andperformance of the WC/Co composite. Residual stresses in the coatings areinteresting as they may be destructive or constructive for the material duringoperation. Blasting is used to change the as-deposited tensile stress to compressive.The usefulness of X-ray diffraction (XRD) and nanobeam diffraction (NBD) forcharacterization of strains in the different coating layers has been investigated. XRDwith different anode materials has been used to determine the macrostress in thelayers and an attempt was done to calculate the average microstrain and crystallitesize. NBD was used to study the microstrain within single grains of the differentmaterials. A specimen preparation method has been developed for the studiedsamples using the FIB.The XRD analysis shows that the measurement condition is of great importanceduring stress measurements. The macrostress of the different samples show that theZrCN type coating is less stressed than the TiCN type coating after deposition. It isalso shown that the ZrCN type coating is less affected by the blasting. Determinationof microstrain and crystallite size from XRD needs further development.The NBD is a good method to evaluate microstrain within single grains, or betweengrains oriented in the same zone axis. The analyses show more strain within thegrains after blasting. The measurements indicate more strain variation in the Al2O3layer in the TiCN system compared to the ZrCN system.

Increasing productivity is a constant demand for the manufacturing industry. Low-carbon-steel is one of the most commonly used ferrous materials in the part manufacturing market. Improving productivity as well as making the process eco-friendly by implementing a dry machining condition is the essential goal of this study. Built-up-edge (BUE) is often formed in the low-carbon-steel machining process, which, results in poor surface finish and short tool life. The high-speed-machining technique can be used to reduce the BUE formation and realize an increase in productivity. Cubic boron nitride (CBN) tools are most commonly used in hard turning and cast-iron machining at high cutting speeds. There are a limited number of studies regarding low-carbon-steel machining with CBN under a high-speed and with a dry machining condition. In this study, the investigation shows the preferable type of CBN tool and the wear mechanisms involved during finish turning operations of AISI 1018 under high speed and dry machining conditions. Test results show that a low CBN content with a TiCN binder and smaller grain size offers the best tool life and surface integrity of the final part. Currently manufacturers use coated carbide tools with a recommended cutting speed of 200-300m/min with coolant to complete the finishing process for turning low carbon steel parts. In this study, by implementing CBN tools under the dry condition at 500 m/min cutting speed (speed was selected from the preliminary test performed using the uncoated CBN from 500 to 1200 m/min), the buildup edge formation has been reduced, tool life was measured to increase by 307% compared to the benchmark tool (Coated Carbide), and surface finish was measured in the range of 0.8-1.6μm Ra. / Thesis / Master of Applied Science (MASc)

Global warming and depletion in fossil fuels have forced the society to search for alternate, clean sustainable energy sources. An obvious solution to the aforesaid problem lies in electrochemical energy storage systems like fuel cells and batteries. The desirable properties attributed to these devices like quick response, long life cycle, high round trip efficiency, clean source, low maintenance etc. have made them very attractive as energy storage devices. Compared to many advanced battery chemistries like nickel-metal hydride and lithium - ion batteries, metal-air batteries show several advantages like high energy density, ease of operation etc. The notable characteristics of metal - air batteries are the open structure with oxygen gas accessed from ambient air in the cathode compartment. These batteries rely on oxygen reduction and oxygen evolution reactions during discharging and charging processes. The efficiency of these systems is determined by the kinetics of oxygen reduction reaction. Platinum is the most preferred catalyst for many electrochemical reactions. However, high cost and stability issues restrict the use of Pt and hence there is quest for the development of stable, durable and active electrocatalysts for various redox reactions. The present thesis is directed towards exploring the electrocatalytic aspects of titanium carbonitride. TiCN, a fascinating material, possesses many favorable properties such as extreme hardness, high melting point, good thermal and electrical conductivity. Its metal-like conductivity and extreme corrosion resistance prompted us to use this material for various electrochemical studies. The work function as well as the bonding in the material can be tuned by varying the composition of carbon and nitrogen in the crystal lattice. The current study explores the versatility of TiCN as electrocatalyst in aqueous and non-aqueous media. One dimensional TiC0.7N0.3 nanowires are prepared by simple one step solvothermal method without use of any template and are characterized using various physicochemical techniques. The 1D nanostructures are of several µm size length and 40 ± 15 nm diameter (figure 1). Orientation followed by attachment of the primary particles results in the growth along a particular plane (figure 2). (a) (b) (c) Figure 1. (a) SEM images of TiC0.7N0.3 nanowires (b) TEM image and (c) High resolution TEM image showing the lattice fringes. (a) (b) (d) Figure 2. Bright field TEM images obtained at different time scales of reaction. (a) 0 h; (b) 12 h; (c) 72 h and (d) 144 h. The next aspect of the thesis discusses the electrochemical performance of TiC0.7N0.3 especially for oxygen reduction. Electrochemical oxygen reduction reaction (ORR) reveals that the nanowires possess high activity for ORR and involves four electron process leading to water as the product. The catalyst effectively converts oxygen to water with an efficiency of 85%. A comparison of the activity of different (C/N) compositions of TiCN is shown in figure 3. The composition TiC0.7N0.3 shows the maximum activity for the reaction. The catalyst is also very selective for ORR in presence of methanol and thus cross-over issue in fuel cells can be effectively addressed. Density functional theory (DFT) calculations also lead to the same composition as the best for electrocatalysis, supporting the experimental observations. Figure 3. Linear sweep voltammetric curves observed for different compositions of titanium carbonitride towards ORR. The next chapter deals with the use of TiC0.7N0.3 as air cathode for aqueous metal - air batteries. The batteries show remarkable performance in the gel- and in liquid- based electrolytes for zinc - air and magnesium - air batteries. A partial potassium salt of polyacrylic acid (PAAK) is used as the polymer to form a gel electrolyte. The cell is found to perform very well even at very high current densities in the gel electrolyte (figures 4 and 5). Figure 4 Photographs of different components of the gel - based zinc - air battery. (a) (b) Figure 5. a) Discharge curves at different current densities of 5, 20, 50 and 100 mA/cm2 for zinc-air system with TiC0.7N0.3 cathode b) Charge – discharge cycles at 50 mA/cm2 for the three electrode configuration with TiC0.7N0.3 nanowire for ORR and IrO2 for OER and Zn electrode (2h. cycle period). Similarly, the catalytic activity of TiC0.7N0.3 has also been explored in non-aqueous electrolyte. The material acts as a bifunctional catalyst for oxygen in non- aqueous medium as well. It shows a stable performance for more than 100 cycles with high reversibility for ORR and OER (figure 6). Li-O2 battery fabricated with a non-aqueous gel- based electrolyte yields very good output. (a) (b) (c) Figure 6. Galvanostatic charge –discharge cycles. (a) at 1 mA/cm2 (b) specific capacity as a function of no. of cycles (c) photographs of PAN-based gel polymer electrolyte. Another reaction of interest in non –aqueous medium is I-/I3-. redox couple. TiC0.7N0.3 nanowires show small peak to peak separation, low charge transfer resistance and hence high activity. The catalyst is used as a counter electrode in dye sensitized a solar cell that shows efficiencies similar to that of Pt, state of the art catalyst (figure 7). (a) (b) (c) Figure 7 (a) Cyclic voltammograms for I-/I3 - redox species on TiC0.7N0.3 nanowires (red), TiC0.7N0.3 particle (black) and Pt (blue). (b) Photocurrent density - voltage characteristics for DSSCs with different counter electrodes. TiC0.7N0.3 nanowire (black), TiC0.7N0.3 particle (blue), Pt (red). (c) Photograph of a sample cell. (a) (b) (c) (d) Figure 8 a) Comparison ORR activity for (i) NiTiO3(black), (ii) N-rGO (red), (iii) NiTiO3 – N-rGO (green) and (iv) Pt/C (blue) (b) Linear sweep voltammograms for OER observed on NiTiO3 – N-rGO composite (black), NiTiO3 (brown), N-rGO (blue), glassy carbon (red) in 0.5 M KOH. (c) Galvanostatic discharge curves of NiTiO3 – N-rGO as air electrode (d) Charge – discharge cycle at 5 mA/cm2 for the rechargeable battery with 10 min. cycle period. The last part of the thesis discusses about a ceramic oxide, nickel titanate. The electrocatalytic studies of the material towards ORR and OER reveal that the catalyst shows remarkable performance as a bifunctional electrode. A gel - based zinc - air battery fabricated with nickel titanate – reduced graphene oxide composite shows exceptional performance of 1000 charge-discharge cycles in the rechargeable mode (figure 8). Of course, the primary battery configuration works very well too The thesis contains seven chapters on the aspects mentioned above with summary and future perspectives given as the last chapter. An appendix based on TiN nanotubes and supercapacitor studies is given at the end.