This thesis reports on the challenge of applying an innovative ‘soft-soft nanocomposite’ design strategy to establish synthesis parameters that affect the performance of coatings based upon water-borne latexes, which is driven by the environmental and legislative need to develop feasible alternatives to solvent-borne coatings. A framework emulsion polymerisation formulation to synthesise core-shell latexes with (poly[(butyl acrylate)-co-(butyl methacrylate)]) core and (poly[(butyl acrylate)-co-(butyl methacrylate)-co-(diacetone acrylamide)]) shell copolymer phases in a controlled manner was established, with high monomer conversions and approximately constant particle numbers. Retention of particle morphology in the films was confirmed using atomic force microscopy (AFM). The effect of adding adipic acid dihydrazide to the latex post-polymerisation to facilitate crosslinking of the shell phase during film formation was found to have a significant effect on the stress-strain properties of latex films. A core:shell mass ratio of 80:20 was found to be optimum in all crosslinked systems tested. Increasing the amount of crosslinking in the shell phase of the particles was found to have an effect on the large strain tensile properties of films, leading to strain hardening with reduced extension to break and higher failure stresses at higher crosslinker levels. Core phase copolymer Tg had a very significant effect upon the low strain mechanical properties, with Young’s modulus values of 5-180 MPa being accessible in the range of core Tg¬s from 5 – 25 oC, although little difference in mechanical behaviour was seen when varying the shell phase Tg from 5 – 15 oC. Adding 2 wt% methacrylic acid (MAA) to the shell phase copolymer gave an additional improvement in the low strain tensile region, with a Young’s modulus of 425 MPa being realised. However, it was found that additional amounts of MAA (up to 5 wt% in the shell phase) were deterious to film properties, with low Young’s modulus and poor extensibility. This was interpreted as being due to an increased concentration of ionomeric crosslinks restricting interparticle chain diffusion and keto-hydrazide crosslinking. Studies to evaluate the mechanical performance of soft-soft nanocomposite films compared to binder latexes used in commercial products were favourable, and showed that a high level of versatility with regards to mechanical properties is possible.

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Thesis (M.Sc.(Engineering)--University of the Witwatersrand, Faculty of Engineering and the Built Environment, School of Chemical and Metallurgical Engineering, 2012,. / The objective of this research was to improve alumina (Al2O3) mechanical and electrical properties by reinforcement using multi-walled carbon nanotubes (MWCNTs) and titanium carbide (TiC). The objective of the study was achieved with interesting and challenging difficulties along the way. The MWCNTs were initially coated with boron nitride (hBN) in order to improve the Alumina-CNTs interface which was previously discovered to be weak and also to protect them from reacting with Al2O3 during sintering. The coating of CNTs with hBN was done using nitridation method. This method was unsuccessful since it was not possible to coat each CNT individually. Dispersing hBN coated CNTs proved to be impossible without pealing the off the hBN coating. The “flaking off “of the hBN coating from the CNTs revealed that the CNT-hBN interface was weak; therefore uncoated CNTs were used for this study. The starting powders (Al2O3, TiC and CNTs) were individually dispersed before they were mixed together. TiC and Al2O3 were dispersed using an ultrasonic probe which was done successfully. The CNTs were dispersed by an ultrasonic probe and then attritor milled with the use of polyvinylpyrolidone (PVP) as a dispersant. The dispersed Al2O3 and TiC (30 wt%) powders were mixed in a planetary ball mill. The composite powder was sieved and sintered using SPS with temperature and pressure programmed to be 1700˚C, 35MPa respectively. In making the Al2O3+CNT composite powder, the already dispersed Al2O3 and CNTs (1 wt%) were mixed in a planetary ball mill, after sieving the powder it was sintered using SPS at 1600˚C, 35MPa (programmed conditions). Lastly in making the Al2O3+CNT+TiC composite, the already dispersed TiC, CNTs and Al2O3 were all mixed in a planetary ball mill, after sieving it was sintered using SPS at 1650˚C, 35MPa (programmed conditions). For comparison of properties, dispersed monolithic Al2O3 was also sintered using SPS at 1600˚C, 35 MPa. The density results showed that the monolithic Al2O3 was 99.8% dense, , Al2O3+CNTs was 99.4%, Al2O3+TiC+CNTs was 99.2% and Al2O3+TiC sample was 99.0%. The mechanical properties of the samples were measured using the indentation method. The hardness and fracture toughness of the samples were; Al2O3= 3.3MPa√m (17 GPa), Al2O3+CNTs = 4.2MPa√m (18 GPa), Al2O3+TiC = 4.8 MPa√m (23 GPa) and Al2O3+TiC+CNT= 5.0 MPa√m (23 GPa). The electrical properties showed that incorporating CNTs and TiC into Al2O3 improved Al2O3 electrical conductivity. The measured electrical conductivity of the ceramic samples were; Al2O3 iii ≈ 0 Sm-1, Al2O3+CNTs= 30 S.m-1, Al2O3 +TiC + CNTs = 6855 S.m-1 and Al2O3+TiC = 9664 S.m-1. The CNTs improved Al2O3 mechanical properties slightly inhibiting grain growth by pinning the grain boundary movement and also by crack bridging. The Al2O3 electrical conductivity was increased by the CNTs network that was located along the alumina grain boundaries. The TiC improved Al2O3 mechanical properties slightly inhibiting grain growth and through crack deflection mechanism. The addition of TiC into Al2O3 increased the electrical conductivity by serving as a conducting continuous secondary phase. The results show that the CNT-hBN interface is weak. The addition of CNTs and TiC into monolithic Al2O3 slightly improved its mechanical and electrical properties but it density was slightly compromised. CNTs and TiC slightly improved monolithic alumina hardness by in inhibiting Al2O3 grain growth and the fracture toughness through crack deflection and crack bridging mechanisms. The CNTs network located at the Al2O3 grain boundaries not only aided in improving Al2O3 hardness but also served as transport medium for electrons hence increasing the Al2O3 electrical conductivity. Addition of TiC into Al2O3 increased its electrical conductivity by conducting electrons from one TiC grain to the adjacent grain. The large increase in electrical conductivity upon addition of TiC is due to the presence of a continuous TiC phase within Al203.

Sobre opiso desenvolvem-se todas as atividades a que se destina a edificação. Falhas Em sua execução, tais como, empenamentos, placas soltas, bolhas e manchas têm como conseqüências, desde o desconforto pessoal de andar em uma superfícieirregular, ao risco de acidentes de trabalho, contaminação de produtos por poeira, de salinhamento de equipamentos ou até mesmo a interferência no processo de produção, podendo provocar a paralisação parcial ou total da atividade produtiva da empresa.Tais problemas, muitas vezes são decorrentes do excesso de umidade do substrato de concreto, quando da aplicação do revestimento, por não ter tido o tempo de secagem adequado, de maneira a atingir o nível de umidade ideal. O excesso de água residual decorrente da umidade do substrato é uma das principais causas geradoras de patologias nos pisos de concreto quando utilizados revestimentos suscetíveis à presença de água. O comportamento da umidade do concreto é resultado de uma complexa ação entre a quantidade de água física e quimicamente ligada, durante a hidratação do cimento e a capacidade de transporte de água do sistema de poros do concreto. Neste contexto, o presente trabalho procura contribuir na sistematização do conhecimento sobre o assunto, descrevendo, inicialmente, o comportamento de bases de concreto frente à ação da água e os fatores que a influenciam: grau de hidratação, condições de equilíbrio e fluxo de umidade. É mostrado como ocorre a secagem do concreto e a influencia do tempo de cura, relação água/cimento do concreto e condições ambientes sobre o tempo necessário para que a umidade do concreto atinja o nível ideal para o início do revestimento do piso. São descritos os testes utilizados para a medição do nível de umidade do concreto, enfatizando os de caráter quantitativo, baseados na medição do teor de umidade, taxa de emissão de vapor de água e umidade relativa interna do concreto. Valores dos níveis ideais de umidade, em conformidade com o tipo de teste aplicado e materiais empregados, estabelecidos por entidades representativas de fabricantes de revestimentos para pisos de concreto, são apresentados como referências. O texto é finalizado com a apresentação das recomendações que visam facilitar a secagem do concreto e aspectos a serem observados quando da realização da medição do nível de umidade. / On the floor are developed all the activities the building is destined to. Faults in its execution, such as warping, loose plates, bubbles and stains, bring about from the personal discomfort of walking on an irregular surface, to the risk of workplace accidents, contamination of product due to dust, misalignment of equipment or even the interference in the production process, which may cause a partial or total stalling of the company productive activity. Such problems often derive from excess moisture in the concrete substrate, when the lining is applied, for not having been dried long enough, so as to attain the ideal moisture level. The excess residual water deriving from substrate moisture is one of the main causes generating pathologies on concrete floors when linings susceptible to the presence of water are used. The moisture behavior of concrete derives from a complex action between the amount of physical and chemically related water, during the hydration of the cement and the water transport capacity of the concrete pore system. In thisn context, the present work aims to contribute in systematizing the knowledge on the matter, initially describing the behavior of the concrete bases concerning the action of water and the factors influencing this: degree of hydration, balance conditions and humidity. The work shows how the drying of concrete occurs and the influence of the curing time flux, concrete water/cement ratio and ambient conditions on the time required for the concrete moisture to attain the ideal level to start the floor lining. The tests used to measure the concrete moisture level are described, emphasizing those of quantitative character, based on the measurement of the moisture content, water vapor emission rate and the concrete relative internal humidity. Values of the ideal levels of moisture, in accordance with the type of test applied and materials employed, established by representative manufacturer entities for concrete floors linings, are presented as references. The text concludes with the presentation of recommendations that aim to make the drying of concrete easier and aspects to be observed when the measurement of the moisture level is performed.

Epoxy coatings are currently the most popular corrosion protection mechanism for steel reinforcement in structural concrete. However, these coatings are easily damaged on worksites, negating their intended purpose. This study investigates self-healing coatings for steel reinforcement to introduce an autonomous healing mechanism for damaged coatings. Coatings were applied to steel coupons, intentionally damaged, and introduced to a corrosive environment via aerated salt-water tanks. Performance of the experimental coatings was evaluated qualitatively and quantitatively. Adhesion strength and effects of coating thickness were also studied. Results from coated steel coupons subjected to damage and submerged in salt-water aeration tanks exhibited improved corrosion resistance performance with self-healing coatings. However, self-healing coatings have comparable poor adhesion to the substrate as do conventional coatings. This paper shows preliminary results demonstrating the potential benefits of self-healing coatings for steel reinforcement and identifies numerous avenues for future research.

Nickel-boron coatings are used to improve friction and wear properties (and, in some cases, corrosion resistance). The nickel-boron coating investigated here is 5-6 wt% boron, and is deposited by electroless plating on a 1018 steel substrate. It is amorphous as-plated, and heat treatment is used to crystallize the coating to improve its hardness. To better understand and predict the effects of heat treatment, samples that had been isothermally annealed at various temperatures from 500ºC to 800ºC for either 2h or 5h were examined by several methods to determine the diffusion effects taking place during annealing. Samples were examined by XRD, both at the coating surface and at multiple depths within the coating. Optical microscopy and SEM were used to view the structure of the coating in cross-section. Cross sections were etched and examined by optical microscopy and SEM, as well as EDS, which was used to develop a Ni-Fe composition profile at the coating-substrate interface. Microhardness measurements were taken and used to develop microhardness profiles. Additional samples were annealed to investigate boron oxidation at the coating surface. Based on the data, there is a reduced amount of Ni3B near the outer surface of the heat-treated coatings, with the thickness of the resultant γ-Ni layer increasing with annealing time and temperature, from 2.4 to just over 13 µm. This low-boron region indicates that boron is diffusing out through the surface of the coating and oxidizing, which the literature indicates should result in the formation of B2O3. Because B2O3 is water-soluble, it is likely that it dissolved during the water quench that concluded most anneals. Diffraction and EDS data also indicate interdiffusion of the nickel in the coating and the iron in the steel substrate. This leads to the formation of a soft interdiffusion layer between the Ni3B coating bulk and steel substrate that appears to be a mix of ferrite and Ni3Fe.

Lead-based and lead-free ferroelectric ceramic materials were prepared at low sintering temperatures with particular regard to their applications in thick film piezoelectric components. This project is focused on the development of processing methods and novel compositions to be used for thick film production by electrophoretic deposition (EPD) on heat-resistant alloys. Lead-based glasses and an oxide mixture (LiCO3, Bi2O3 and CuO), denoted LBCu, with low melting points were used as sintering aids for lanthanum-doped lead zirconate titanate (PLZT) ceramics. The required temperature to achieve dense ceramics was reduced from 1250 to 950 °C. It was found that the highest ferroelectric properties were obtained by the use of LBCu in comparison with those incorporating glass additives due to the shielding effect of the glass phase between the ferroelectric grains. However, the results of thick film preparation shown that the samples with glass additives were much smoother and relatively free of cracks up to 1000 ÂoC. In terms of lead-free ceramics, novel compositions were prepared, based on (Ba,Ca)(Zr,Ti)O3-(K0.5Bi0.5)TiO3 (BCZT-KBT) solid solutions having various Ca and Zr contents. The new solid solutions exhibited interesting features comprising core-shell type microstructures and relaxor ferroelectric behaviour in addition to reduced sintering temperatures and higher Curie point compared with BCZT ceramics. The required sintering temperature reduced to 1125 °C at 65% KBT, in comparison with 1500 °C for pure BCZT. The results showed that the compositional heterogeneity in the shell regions was reduced by air quenching, relative to that of the slow-cooled state, due to the retention of the more chemically-homogeneous high temperature state by the quenching process. The improvements were evident in increased polarisation, piezoelectric coefficient and depolarisation temperature values. However, the slow-cooled samples exhibited high reversible strain levels due to the presence of polar nanoregions (PNRs) in the ergodic state within the shell regions. Comparing the results obtained for two BCZT compositions, it was demonstrated that the stability of the ferroelectric tetragonal phase in slow-cooled BCZT-KBT samples was improved for the ceramic with lower Ca and Zr concentrations, denoted x=0.06, in comparison with that for higher levels, denoted x=0.15. Moreover, the electric field-induced ferroelectric state in the quenched ceramic with x=0.06 was found to be more stable during heating, giving rise to an enhanced depolarisation temperature.

No description available.

by Ku, Nim Chung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references. / by Ku, Nim Chung. / Acknowledgment --- p.i / Abstract --- p.ii / Table of contents --- p.iv / List of figures --- p.viii / List of tables --- p.xiv / Chapter Chapter One --- Introduction / Chapter 1.1 --- History of permanent magnet materials --- p.1 / Chapter 1.2 --- NdFeB intermetallic compound --- p.4 / References --- p.8 / Chapter Chapter Two --- Background / Chapter 2.1 --- Corrosion and corrosion control --- p.9 / Chapter 2.1.1 --- Electrochemical mechanisms --- p.10 / Chapter 2.1.2 --- Types of corrosion cell --- p.12 / Chapter 2.1.3 --- Types of corrosion --- p.14 / Chapter 2.1.4 --- Corrosion control --- p.15 / Chapter 2.2 --- Intermetallic compounds and phases --- p.19 / References --- p.26 / Chapter Chapter Three --- Instrumentation / Chapter 3.1 --- Introduction --- p.27 / Chapter 3.2 --- Vacuum evaporator --- p.28 / Chapter 3.3 --- Vacuum furnace --- p.29 / Chapter 3.4 --- Scanning electron microscopy (SEM) & Energy dispersive analysis (EDX) --- p.29 / Chapter 3.5 --- Corrosion chamber --- p.31 / Chapter 3.6 --- Vibrating sample magnetometer (VSM) --- p.31 / References --- p.43 / Chapter Chapter Four --- Moisture corrosion test on a bare NdFeB permanent magnet (without any coating) / Chapter 4.1 --- Introduction --- p.44 / Chapter 4.2 --- Experimental procedures --- p.45 / Chapter 4.3 --- Results from visual inspection --- p.45 / Chapter 4.4 --- Corrosion behavior --- p.46 / Chapter 4.5 --- Measurement of the saturated magnetization --- p.47 / Chapter 4.6 --- The effect of corrosion on the magnetic property of the NdFeB magnet --- p.48 / Chapter 4.7 --- Conclusions --- p.49 / References --- p.57 / Chapter Chapter Five --- Interfacial reaction between the A1 coating and the NdFeB magnet / Chapter 5.1 --- Introduction --- p.58 / Chapter 5.2 --- Experiments --- p.59 / Chapter 5.3 --- The Interaction between the A1 coating and Magnet --- p.60 / Chapter 5.4 --- Conclusions --- p.63 / References --- p.67 / Chapter Chapter Six --- Corrosion behavior of A1 coated NdFeB magnet in moist environment / Chapter 6.1 --- Introduction --- p.68 / Chapter 6.2 --- Experiments --- p.69 / Chapter 6.3 --- Results --- p.69 / Chapter 6.3.1 --- The annealed samples before corrosion test --- p.70 / Chapter 6.3.2 --- Microstructure changes after 3 days of corrosion --- p.70 / Chapter 6.3.3 --- Corrosion process in the annealed samples --- p.71 / Chapter 6.4 --- Corrosion behavior --- p.73 / Chapter 6.4.1 --- Effects of NaCl on the samples --- p.73 / Chapter 6.4.2 --- Effects of the inter-diffusion --- p.74 / Chapter 6.5 --- Conclusions --- p.75 / References --- p.79 / Chapter Chapter Seven --- Dual layer coating of either Ti/Al or Ni/Al on the NdFeB permanent magnet / Chapter 7.1 --- Introduction --- p.80 / Chapter 7.2 --- Experiments --- p.81 / Chapter 7.3 --- The Interaction between the A1 and Magnet --- p.81 / Chapter 7.3.1. --- The Ti/Al coated magnets --- p.82 / Chapter 7.3.2. --- The Ni/Al coated magnets --- p.83 / Chapter 7.4 --- Volume contraction of the intermetallic coatings --- p.84 / Chapter 7.5 --- Conclusions --- p.85 / References --- p.90 / Chapter Chapter Eight --- Conclusions and suggestions for further studies --- p.91

No description available.