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Recent developments in the field of nano-structured materials for technological as well as scientific prospective are quite interesting. In this context carbon plays a dominant role. Few examples such as carbon nanotubes (CNTs), fullerene, nanostructured diamond, as well as, amorphous carbon film, particularly, diamond-like carbon (DLC) coating are the areas of today’s research. This thesis deals with ECR plasma deposition of carbon in two different forms, i.e., Diamond-like carbon (DLC) and carbon nanotubes (CNTs) In the case of DLC coatings the chemical vapor deposition (CVD) and sputtering CVD configuration has been used. The carbon nanotubes have been grown using CVD configuration. DLC films were deposited by ECR-rf CVD mode, as well as, ECR sputtering mode. In case of CVD films, about 0 — 100 Watts rf bias was employed in steps of 20 Watts, corresponding to effective negative self bias voltage of 15 — 440 V. CH4 and C2H2 have been used as source gas for CVD films. Microwave power was optimized at 300 Watts. In case of sputtering, a cylindrical graphite target (diameter 9 cm and length 6 cm) kept at the exit of the Ar plasma was biased with -200 V. Films were deposited on floating substrate (temperature ~100 oC). Films were deposited on Si, quartz, and steel substrates and characterized by FT-IR, Raman, UV-Visible, Photoluminescence spectroscopy (PL), spectroscopic ellipsometry. Nanoindentation was used to evaluate the film’s elastic property. Pin-on-disk measurement was used to study the tribological property of the films. Electrical properties of the films deposited on Si [p-(100), 10 Ω cm] were studied using picoammeter / source measuring instrument by two probe method. FT-IR analysis showed sp3C-H absorption peak at 2930 cm-1 for the CVD films, while sputtered films did not show any C-H absorption. Raman spectroscopy was used to evaluate bonding aspects as well as hydrogen content of the films. Comparison of sp3C : sp2C among the films was done based on I(D) / I(G) of the Raman peaks, while hydrogen content was estimated based on background slope of the Raman spectra. It was observed that increase in rf bias induces more sp2C while hydrogen content decreases. An optimum substrate bias of 40 Watts was predicted from the Raman spectra. For sputtered films Raman spectra indicated the formation of nanocrystal diamond in a-C matrix. UV-Visible-NIR optical transmission spectroscopy was used to determine the band gap (Tauc), E0, of the films. It showed that increase in rf bias increases the absorption coefficient α. The films deposited from CH4 with a substrate bias of 0 and 20 Watts (i.e., high hydrogen content in the film) followed (hνα)1/2 = const. (hν –E0), while other films hνα = const. (hν –E0) ( h is Plank constant ν is frequency of light). E0 varied from 1.1 — 2.5 eV. It was assumed that for π--π* transition follows root relation while π--σ * transition follows linear relation. Spectroscopic ellipsometry was used to determine optical constants, film thickness, and interface thickness. Deposition rate found out to be ~100 nm / mints for C2H2, ~10 nm / mints for CH4, and ~2.5 nm /mints for sputtered films. Formation of interface layer of thickness about 5 —30 nm due to high energy ion bombardment takes place for the films deposited at 40 Watts rf bias or higher. Band gap and related phenomena was revisited from the data that was obtained from this instrument which reasonably matches with the earlier results. PL experiments were carried out at room temperature using lamp excitation source as well as laser excitation source (457.9 nm wavelength). In case of lamp excitation source any wavelength from 200 —900 nm region can be selected. PL spectra showed that there are two sources of PL signal, one from nanocrystal diamond and other from sp2C phase. To obtain PL signal from diamond UV excitation wavelength was required. This diamond phase is highly efficient emitter as compared to sp2C phase. Based on the closeness of diamond’s optical centre labeling of the peaks was done. For CVD films N3 ( 457 nm), H4 (495 nm), H3 (520 nm), [N-V]0 (~590 nm) optical centers of diamond was observed. For sputtered films [N-V]0 (2.08 eV), H3 (2.38 eV), H4 (2.50 eV), N3 (2.81eV), N3 (2.96 eV), 3.3 eV ( undocumented peak), 5RL ( 4.14 eV) optical centers of diamond as well as band-edge emission (5.01 eV ) was observed. Nanoindentation technique was used to estimate the elastic property and related phenomena of the films. It shows that the films are having hardness of 5—17 GPa and reduced modulus of 20 —120 GPa depending on the deposition parameters. All the films show highly elastic response at lower load, i.e., at low indentation depth where elastic recovery is 85—95 %. At higher load substrate effect comes into the picture. Further morphology in and around the region was evaluated using scanning probe microscopy (SPM). It was shown that substrate effect comes into picture that is based on film’s thickness as well as its elastic property. Films were further characterized by pin-on-disk experiments. C2H2 based films were used because of high deposition rate. Since 40 Watts, 60 Watts, and 100 Watts films adhere well with steel only on these films tribological test was possible. A hardened bearing-steel was used as substrate and a 2 mm diameter cylindrical pin made of tool steel was use as pin. Studies were carried out with three different loads of 20, 40, and 60 N. Friction coefficient varied from 0.02 — 0.04 and wear rate was found to be 10-6 — 10-9 mm3 / N m. A sputtered film of 0.1 μ m on the top of the CVD film, in many respects, enhances the tribological properties. It was shown that certain amount of wear is required for low friction of DLC. Electrical characterization of the films deposited from CH4 showed that they are highly insulating with resistivity of 1013 —1011 Ω-cm, and current conduction mechanism has been found to be predominantly space charge limited conduction (SCLC). Similar to the observations of Tauc’s relation, the film deposited with 0 and 20 Watts bias behave differently and followed the relation , where as, all other films exhibited the relation ( α, n are constants). It signifies that for 0 and 20 Watts rf biased films traps are uniformly distributed across the band gap while for others it decreases from the conduction band. For 0 and 20 Watts rf biased films no Ohmic current was observed at a detection level of 10-11 A. 40 Watts and higher rf biased films showed that three distinct regions in the I-V curves; initially Ohmic region, next to it SPLC region, and finally breakdown region. Increase in rf bias causes increase in Ohmic current. Film deposited from C2H2 showed diode-like behavior with higher conduction current limited by resistive control, and the resistivity of the films was ~ 109 — 105 Ω-cm. Difference in resistivity between the films deposited from CH4 and C2H2 was explained by considering the impurities in the source gas resulting in nitrogen doping concentration. Increase in Ohmic current for the CH4 films was explained by assuming the widening of the σ--σ * gap. Similar diode-like behavior was observed with the sputtered film. The last part of the work deals with the growth mechanism of aligned CNTs and their field emission (FE) properties. Nanotubes were grown at 700 0C on Ni coated (thickness 40 nm, 70 nm, and 150 nm) Si substrate using a mixture of CH4 and H2 gas. Microwave power of 500 Watts was optimized for nanotube growth. Nickel nanoparticle formation mechanism from a continuous Ni film was explained by considering the stress that is generated due to the difference in thermal expansion coefficients of Si and Ni at 700 oC. Though the thicker film such as 150 nm does not form nanoparticle due to stress, hydrogen induced fragmentation of the film due the brittleness of the film even causes formation of finer nanoparticles. A substrate bias in the range 0— 250 V was used to align the nanotubes. Perfectly aligned CNTs were obtained at -250 V substrate bias. The density of the tubes varied from 108 —109 / cm2 while its length was 0.5 — 2 μ m. Due to hydrogen induced fragmentation of the films, 150 nm Ni thick film showed smallest diameter 2 — 5 nm CNTs. 40 nm films showed nanotube diameter of 10 — 30 nm and 150 — 300 nm while 70 nm showed 10 — 30 nm diameter nanotubes. Diameter of the nanotubes was estimated using transmission electron microscopy (TEM). Field emission analysis of these CNTs was done using Fowler-Nordheim (F-N) plot and the investigation revealed that the field emission properties strongly depend on density and aspect ratios. The non-linearity in the F-N plot or current saturation phenomena was explained in terms of change in work function due to heating effect during FE which was pronounced in case of longer nanotube. Suitable efficient cold-cathode emitters for a particular usage (assuming that the variables are applied field and emission current) could be designed from the obtained results. An ammonia gas sensor using thick nonaligned CNTs was realized. For this purpose a thick film of CNTs (~ 0.5 μm) was deposited. This sensor can detect 100 ppm level of ammonia. About 1.5 — 4.5 % change of resistance depending on ammonia concentration (100 —1000 ppm) was observed.

Inscrite dans le cadre d’un projet ANR, la thèse porte sur l’étude et le développement des revêtements poudres UV en vue du recouvrement de panneaux de bois. La thèse détaille les spécificités de ces formulations et de la technologie associée afin de constituer une bibliographie solide propre à ce domaine. Les travaux expérimentaux se basent sur des formulations modèles comprenant une résine poudre UV (uréthane diacrylate ou polyester diméthacrylate) et un photoamorceur. Une étude mécanistique permet de montrer les influences de la température et de la viscosité, de l’intensité lumineuse et de l’atmosphère sur la réactivité des formulations modèles. Il est également démontré que les mécanismes de terminaison spécifiques à ces systèmes suivent des processus mixtes: bimoléculaire, pseudo-monomoléculaire et recombinaison des radicaux primaires. La prédominance des différents processus dépend de l’avancement de la réaction. La formation du réseau de réticulation est ensuite étudiée en fonction de la source d’irradiation: convoyeur semi-industriel doté de lampes UV ou système LED émettant autour de 395 nm. Les caractéristiques du réseau de réticulation (Tg, densité de réticulation, module d’Young) sont reliées aux propriétés des revêtements finaux (flexibilité, résistance à la rayure ou au solvant). L’utilisation d’acrylates multifonctionnels a un impact sur les longueurs de chaînes et la densité de réticulation. En vue d’applications spécifiques, il est finalement proposé d’incorporer une argile modifiée avec de l’Argent au sein des formulations modèles pour obtenir des revêtements poudres UV antibactériens homogènes possédant de bonnes propriétés de résistance. / In the frame of a project of the Agency National Research (France), the thesis deals with the study and the development of UV powder coatings dedicated to wood based panels. The work describes the main features of these formulations and the associated technology in order to offer a strong bibliography specific to this area. The experiments are based on model formulations containing an UV powder resin (diacrylate urethane or dimethacrylate polyester) and a photoinitiator. A mechanistic study allows highlighting the influence of temperature and viscosity, light intensity and atmosphere on the reactivity of the model formulations. It is also shown that the termination mechanisms specific to theses systems follow mixed processes: bimolecular, pseudo-monomolecular and primary radical termination. The predominance of the different processes is related to the reaction conversion. The building of the crosslinking network is then studied depending of the irradiation source: semi-industrial conveyor equipped with UV lamps or LED system emitting around 395 nm. The characteristics of the crosslinking network (Tg, crosslinking density, Young’s modulus) are linked to the final coatings properties (flexibility, scratch and solvent resistance). The incorporation of multifunctional acrylates affects the chains length and crosslinking density. To reach specific applications, it is finally proposed to add a silver-modified clay into model formulations to obtain homogeneous antibacterial UV powder coatings exhibiting good resistance properties.

The proposed dissertation thesis deals with the characterization of HVOF and APS-thermally sprayed coatings prepared on the AZ31 and AZ91 magnesium substrates. The theoretical part of the thesis describes in-detail Mg substrates used in the experimental part of the thesis. There are also characterized materials and coatings based on NiCrAlY and FeCrNiMoSiC metals, WC-CoCr cermets, and YSZ ceramic materials. At the end of the theoretical part, the literary research summarizing the characterization and analysis performed on thermally sprayed coatings on Mg alloys. Based on the theoretical knowledge, the characterization of Mg substrates and deposited coatings was performed in terms of the surface morphology, microstructure, and the chemical composition using the light microscopy (LM) and scanning electron microscopy with energy-dispersive spectroscopy (SEM+EDS). The phase composition of the coatings was analyzed using the X-ray diffraction (XRD). The diffractions corresponding to the sprayed coatings were compared with the feedstock powders, i.e. materials used for the spraying of the coatings. The characterization of the prepared coatings in terms of the mechanical and tribological properties was performed. The hardness and microhardness of the coatings as well as the coefficient of friction, and the wear rate were measured. The last chapter of the experimental part deals with the evaluation of the electrochemical corrosion properties by the potentiodynamic measurements in a 3.5% NaCl solution. In the case of exposed samples, the evaluation of the surface and coating/substrate interface was performed using LM and SEM with EDS. The mechanism of the corrosion attack and degradation was determined from the acquired knowledge and base on the results of the short-term measurements. Based on the measured results, it can be stated that the deposited coatings were successfully applied on the surface of both Mg alloys. All the coatings increase the surface hardness of the Mg alloys and significantly improve their tribological properties. However, except for FeCrNiMoSiC coatings, the corrosion properties of Mg alloys deteriorate due to the fact that the corrosion environment can pass through the coating to the less noble Mg substrate and the corrosion microcells are created.

No description available.

No description available.

Thesis (MBA)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Retailing is a common modern day phenomenon for which there are many angles of research widely and easily available. Retailing in the context of the global paint and coatings industry however, is a more specified and unique field of study of which resources for research are few. Having had the opportunity of a first-hand close-up inside look into, not only one of the world’s leading paint and coatings companies, but also the global leader in company-owned paint and coatings retailing. This global leader not only led to the origin of my research, but also rekindled the passion within for the global paint and coatings industry and trade. Prior to my employment by PPG, towards the end of 2013, I intentionally embarked on a journey with The Sherwin Williams Company during 2011 to 2013, in collaboration with my current employer at the time, Duraline paints, who afforded me the opportunity only a few people had or ever will.. During the course of four years, I had the opportunity to not only meet a series of wonderful people across the various segments, as well as internal departments of the Sherwin Williams Company globally. Additionally I also had the opportunity to visit the company’s headquarters, 101 Prospector Avenue, Cleveland, Ohio, on numerous occasions whilst staying in close proximity for the duration of the training and strategic planning sessions, in preparation to duplicate the SHW in South Africa. During my involvement with The Sherwin Williams Company, it was evident that the backbone of the company’s sales model, was the consistency as well as continuous growth of the Paint Stores Group; which is the leading North American retail segment of SHW. Since 2011, in an effort to establish the best method of implementation of this sales model in South Africa, various concepts were explored from several angles. It became evident that much research was required to establish feasibility of the SHW sales model in South Africa. Preliminary research however, would have had to be conducted of what the SHW sales model entailed and how it would benefit the company in being a global leader, thereby also exploring the possibility of it being an industry best practice as foundation to what was precisely required to be implemented in South Africa, prior to establishing feasibility in South Africa. The preliminary research became the primary and sole focus of this research project, not only fulfilling the research needs as explained above, but also to serve as evidence of what I perceived the SHW company and the Paint Stores Group to be whilst dealing with the company.

<p>Razvijene su TiAlN/TiSiN i CrAlN/TiSiN nanoslojne prevlake u kojima je napravljen spoj nanoslojnog i nanokompozitnog dizajna. Akcenat je stavljen na proizvodnju prevlaka visoke tvrdoće i visoke otpornosti na lom. Proučavane su i jednoslojne TiAlN, nanokompozitne TiSiN i višeslojne TiAlN/TiSiN prevlake kako bi se utvrdilo kako dizajn utiče na osobine prevlaka. Sve prevlake pripremane su sa jednim, dva i tri stepena rotacije. Pokazano je da dizajn i vid rotacije značajno utiču na mikrostrukturu i teksturu prevlaka, a time na njihove mehaničke osobine, otpornost na lom, adheziju između prevlake i podloge, topografiju površine i tribološko ponašanje. Nanoslojne i nanokompozitne prevlake odlikuju se kompaktnom nanokristalnom mikrostrukturom, dok jednoslojne TiAlN prevlake imaju stubastu strukturu sa kristalnim zrnima veće veličine. Pri prelasku sa jednog na više stepeni rotacije mikrostruktura prevlaka postaje kompaktnija sa kristalnim zrnima manje veličine i manjom poroznošću. U skladu sa tim, najmanju hrapavost, najveću tvrdoću, najveću otpornost na lom i najveću otpornost na habanje imaju nanoslojne i nanokompozitne prevlake pripremane sa dva i tri stepena rotacije.</p> / <p>With the aim to develop hard coatings characterized by both, high hardness<br />and high resistance to cracking, synergy between nanolayered and<br />nanocomposite design was made and nanolayered TiAlN/TiSiN and<br />CrAlN/TiSiN coatings were produced. Monolayer TiAlN, nanocomposite<br />TiSiN and multilayer TiAlN/TiSiN were also studied in order to find the<br />relation between the coating design and their properties. All coatings were<br />deposited with 1-fold, 2-fold and 3-fold rotation. It is shown that coating<br />design and type of rotation have great influence on coating microstructure<br />and texture, and in this way on their mechanical properties, resistance to<br />cracking, adhesion between coating and substrate, surface topography and<br />tribological behavior. Nanolayered and nanocomposite coatings are<br />characterized by compact nanocrystalline microstructure, while monolayer<br />TiAlN coatings have columnar structure with larger crystalline grains. By<br />increasing the number of rotational degrees from 1-fold to 3-fold size of<br />crystalline grains decreases and microstructure becomes more dense.<br />Therefore, nanolayered and nanocomposite coatings deposited with 2-fold<br />and 3-fold rotation are characterized by the highest hardness, highest<br />resistance to cracking, highest wear resistance and the smoothest surface<br />topography.</p>

As ligas de alumínio vêm sendo amplamente usadas nas indústrias aeronáuticas e automobilísticas por suas propriedades mecânicas superiores às do metal puro. Entretanto, como as propriedades de corrosão dessas ligas variam, sendo piores do que as do alumínio puro, surge a necessidade de estudos de diferentes métodos de proteção contra a corrosão. O uso de coberturas protetoras é uma alternativa para diminuir os processos corrosivos e, desta maneira, aumentar a vida útil desses materiais. Das coberturas de conversão existentes, as mais usadas ainda são à base de cromo, porém o cromo tem se mostrado danoso ao meio ambiente e à saúde humana. Por outro lado, as coberturas de conversão à base de óxidos de cério, ambientalmente mais corretas e menos nocivas, já têm sido usadas com sucesso para este propósito. Ademais, partindo do consenso sobre o bom desempenho da polianilina (PAni) em proteger metais oxidáveis contra a corrosão, inclusive o alumínio e suas ligas, o presente estudo propõe o desenvolvimento de proteção anticorrosiva de ligas de alumínio pela combinação de camadas de conversão à base de óxidos de cério associada com camadas de PAni nas ligas de alumínio das séries AA1xxx e AA6xxx. A combinação de camadas duplex surge como uma alternativa promissora por: (i) possibilitar a formação de pontos de ancoragem sobre a superfície, promovidos pelas camadas de conversão à base de óxidos de cério, para a posterior deposição de PAni; (ii) ampliar o uso das camadas de conversão à base de óxidos de cério isoladamente ou combinadas com PAni e (iii) promover o melhor sinergismo na proteção contra a corrosão das ligas de alumínio e de outros materiais pela associação e maior interação desses sistemas. / Aluminium alloys have been widely used in automobile and aircraft industries for their superior mechanical properties to the pure metal. However, as the corrosion properties of these alloys vary, being worse than those of pure aluminium, there is a need for studies of different methods of corrosion protection. The use of protective coverings appears as an alternative to reduce the corrosion process and thereby increase the useful life of these materials. Conversion of existing coverage, the most used are still based on chrome, but chrome has proven harmful to the environment and human health. Furthermore, coverage of cerium-based conversion, more environmentally friendly and healthy, have already been successfully used for this purpose. Furthermore, based on the consensus on the proper performance of polyaniline (PAni) to protect oxidizable metals against corrosion, including aluminium and its alloys, this study proposes the development of corrosion protection of aluminium alloys by combining layers of cerium conversion associated with layers of polyaniline on aluminium alloys AA1xxx and AA6xxx series. The combination of double layers arises as a promising alternative, which may: (i) facilitating formation of anchor points on the surface, driven by layers of cerium conversion, for the subsequent deposition of PAni (ii) expand the use of cerium conversion coatings alone or combined with PAni and (iii) promote synergy in protection against corrosion of aluminium alloys and other materials by the association and greater interaction of these systems.