Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Various types of anionic, non-ionic, cationic and zwitterionic additives are used in the coatings industry for the production of paints and colourants. These additives are added to enhance properties such as stabilization of pigment dispersions, wetting of pigments and improvement of open time and freeze/thaw stability. Very often the exact chemistry of these commercial additives is unknown and this is a limitation for new product developments. The identification and characterization of these multi-component polymeric materials continues to be a challenging task. This research presents the use of various advanced analytical techniques to identify and characterize commercial additives that are used in a multi-component colourant formulation. The focus of the present study is on additives that are based on poly(ethylene glycol) (PEG). The molar mass distribution of PEG-based additives was determined with liquid chromatography coupled to mass spectrometry (LC-MS) using solvent gradient elution and at critical conditions of adsorption (LCCC) of PEG. Using the combination of LC-MS, proton nuclear magnetic resonance spectroscopy (1H NMR), pyrolysis gas chromatography (py-GC-MS) and Fourier transform infrared spectroscopy in attenuated total reflectance mode (FTIR-ATR), different additives were identified in terms of the number and type of polymer end groups. The efficiency of the extraction and identification protocol was demonstrated for a blend of additives in a colourant formulation. / AFRIKAANSE OPSOMMING: Verskeie tipes anioniese, nie-ioniese, kationiese en zwitterioniese bymiddels word gebruik in die bedekking nywerheid vir die vervaardiging van verwe en kleurmiddels. Hierdie bymiddels word bygevoeg om sekere eienskappe, soos die stabilisering van pigment dispersie, benatting van pigmente en die verbetering van ope tyd en vries/dooi stabiliteit te versterk. Dikwels is die presiese chemie van hierdie kommersiële bymiddels onbekend en het dit ʼn beperking vir nuwe produk ontwikkeling tot gevolg. Die identifisering en karakterisering van hierdie meer-komponent polimeriese materiaal duur voort om ʼn uitdagings te wees. Hierdie navorsingstudie stel voor die gebruik van verskeie tegnieke om kommersiële bymiddels te identifiseer en karakteriseer wat in meer-komponent kleurmiddel formulasies gebruik word. Die fokus is geplaas op bymiddels wat gebaseer is op poli(etileen glikol) (PEG). The molêre massa verdeling van PEG-gebaseerde bymiddels was bepaal met vloeistofchromatografie gekoppel tot massaspektrometrie (VC-MS) met die gebruik van oplosmiddel gradient eluasie en by kritiese toestande van adsorpsie (VCKT) van PEG. Deur die kombinasie van VC-MS, proton kern magnetiese resonansie spektroskopie (1H KMR), pirolisegaschromatografie (pir-GC-MS) en Fourier-transformasie infrarooi spektroskopie in verswakking totale refleksie modus (FTIR-VTR), is verskillende bymiddels geïdentifiseer in terme van die hoeveelheid en tipe polimeer eindgroep teenwoordig. Die doeltreffendheid van die ekstrahering en identifisering protokol is gedemonstreer vir ʼn mengel van bymiddels in ʼn kleurmiddel formulering.

Coatings are often used as a means of protecting aluminum alloy and steel structures in industry. The assessment of corrosion under these coatings can be challenging. Corrosion sensing coatings can exhibit properties that allow undercoating corrosion to be identified before it can be seen with the naked eye. This would be very advantageous and could potentially result in tremendous savings in time and money when structures undergo routine maintenance. Our work involved the study of corrosion sensing coatings with incorporated fluorescent indicators that can be used to sense the undercoating corrosion on metal substrates. The fluorescent indicator in the coated-aluminum system was a negative indicator, i.e. the indicator in the coating was initially fluorescent and subsequently non-fluorescent due to the reduced pH at the anodic sites of corrosion. The fluorescent indicator in coated-steel system was positive, in the sense that the coating changed from non-fluorescent to fluorescent over the cathodic areas due to increased pH. The corrosion sensing coating was composed of commercial epoxy-polyamide and the indicator: 7-amino-4-methylcoumarin (7-AMC) for the coated-aluminum alloy system and 7-diethylamino-4-methylcoumarin (7-DMC) for the coated-steel system. The feasibility of using 7-AMC for sensing early undercoating corrosion was demonstrated by using fluorescent observations, Electrochemical Impedance Spectroscopy (EIS), Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) tests. EIS results estimated that with continuous immersion the undercoating corrosion occurred within 24 hours after immersion in the salt solution. When corrosion occurred, the corrosion was invisible under natural light. However, small spots appeared in the fluorescent image, changing from initially fluorescent to non-fluorescent where the anodic sites were identified by SEM and EDS. In other words, the fluorescent indicator could sense the early undercoating corrosion, although blistering can be a competing mechanism associated with corrosion under some conditions. The sensitivity of the 7-AMC corrosion detection system was tested by applying anodic current to the metal and measuring the charge at which fluorescence quenching was detected. The critical charge for a detectable pit under the coating was approximately 2x10⁻⁵ C, which implied a critical radius of a single corrosion spot or set of spots of approximately 10 [mu]m. The fluorescent properties of 7-AMC, its effect on the protectiveness, its sensitivity to pH and its concentration in the coating are explored as well. Fourier transform spectroscopy (FTIR) was used to characterize the structure of the coating with and without 7-AMC. The results suggested that there is no structure change occurring after adding 7-AMC into the coating. Fluorescence behavior, electrochemical behavior, microscopic evidence, and visual observations of coated steel specimens with 7-DMC are compared based on exposure to saltwater conditions. Some of the challenges associated with the use of these types of coatings will be presented. This includes the interference from the increased production of ferrous and ferric ions. All of this information is aimed at the development of corrosion sensing coatings that can reveal undercoating corrosion before it is visible to the naked eye. / text

The reactions of atomically clean, titanium film surfaces with oxygen, deuterium, and water have been investigated. Auger Electron Spectroscopy was utilized to monitor the formation 9f a surface oxide in the case of oxygen exposure, and to characterize the deuteride which formed upon deuterium absorption, and its subsequent oxidation. Quantification of surface oxide stoichiometries was facilitated by novel data acquisition and treatment schemes. The quartz crystal microbalance was used to measure the mass of adsorbed oxygen or deuterium with submonolayer sensitivity. Electron energy loss spectroscopy was sensitive to the presence of Ti⁺³ in the surface oxide. The initial oxidation of the titanium surface was characterized by the dissociative adsorption of three mono1ayers of oxygen atoms at a constant rate. The oxide formed during this reaction stage was a Ti₂0₃/Ti0₂ mixture with a total thickness of 13 A. The rate of oxygen adsorption then decreased such that oxide growth was logarithmic with time. When the oxide had attained a total thickness of 20 A, the initial suboxide was converted to Ti0₂, and subsequent oxide formed was purely Ti0₂. Oxide growth occurred by oxygen anion migration under the influence of an electrostatic field, set up across the oxide layer by electron transfer from the metal to adsorbed oxygen species. The pressure dependence of the oxide growth rate and terminal thickness suggested a constant field growth mechanism. Clean titanium films reacted with deuterium to form a bulk deuteride TiDₓ (x<2). The oxide layer which resulted from oxygen exposure was characterized by the above techniques. Oxide layers greater than 20 A completely inhibited deuterium absorption by prohibiting 02 dissociation, but did not act as a diffusional barrier when additional dissociation sites were provided. Iron adlayers were found to accelerate the D₂ absorption reaction. Removal of the titanium films from the vacuum chamber to an isolable electrochemical reaction chamber, without exposure to the atmosphere, allowed a determination of the effect of the various gas/solid reactions on the subsequent electrochemical oxidation processes.

No description available.

AB SOMAS Ventiler manufactures valves for different applications. A valve of type DN VSSL 400, PN 100, used in high-temperature and high-pressure applications was investigated in this thesis. This type of valve is coated with high cobalt alloys to achieve the tribological properties needed for this severe condition. However there is a request from AB Somas Ventiler to find another solution. This request is based on the fact that demands on higher temperatures, from customers, yields higher requirements on the material. It is also a price issue since cobalt is quite expensive. Materials investigated were high-nitrogen steel, Vanax 75, nickel-based superalloy Inconel 718 and hardened steels, EN 1.4903 and EN 1.4923 presently used as base material in the valve. Calculation of contact pressure that arises when the valve is closed was first approached by using finite element method (FEM). Several models were constructed to show the behavior of the valve during closing in terms of deformation. Hot wear tests, in which a specimen was pressed against a rotating cylinder, were performed to be able to compare the materials to the solution of today and among each other. Data extracted from the tests were compiled in the form of coefficients of friction. Profilometer examinations were used to reveal the volumes of worn and adhered material and together with scanning electron microscopy (SEM) the wear situation for each material couple could be assessed. Wear mechanisms detected in SEM were adhesive and abrasive and the results clearly showed that the steels were not a good solution because of severe adhesive wear due to the similarity of mating materials creating a more efficient bonding between the asperities. Vanax 75 showed much better performance but there was still an obvious difference between the steels and the superalloy in terms of both coefficient of friction and amount of wear. On this basis, Inconel 718 was selected as the most suitable material to replace the high cobalt alloys used in the valves today. / AB Somas ventiler är ett företag som tillverkar ventiler för ett brett spann av applikationer. I det här examensarbetet har undersökningar genomförts på en ventil av modell DN VSSL 400, PN 100, som normalt används i applikationer för höga tryck och höga temperaturer. Ventilen beläggs i dagsläget med höghaltiga koboltlegeringar för att uppnå de tribologiska egenskaper som krävs i de påfrestande arbetsförhållanden som råder. AB Somas Ventiler har dock framfört en förfrågan om att hitta en alternativ lösning, en förfrågan som grundar sig i att kundernas ständiga önskemål på att ventilerna ska klara högre arbetstemperaturer också medför högre krav på ventilmaterialen. Det är även en prisfråga, då kobolt är en dyr legering att använda sig av. De material som inkluderades i undersökningen var det kvävelegerade stålet Vanax 75, nickelbaserade superlegeringen Inconel 718 samt de två stålen EN 1.4903 och EN 1.4923 i härdat tillstånd. De två sistnämnda används idag som basmaterial i ventilen. Genom att använda den finita element metoden (FEM) kunde en första beräkning göras av det kontakttryck som uppstår då ventilen stängs. Flera modeller konstruerades för att simulera ventilens deformation vid stängning. Där efter utfördes nötningstester i hög temperatur på de alternativa materialen, genom att låta en provbit pressas mot en roterande cylinder, för att sedan kunna göra en jämförelse mellan materialen och även med den nuvarande lösningen. Från nötningstesterna erhölls data som kunde användas för att ta fram friktionskoefficienter för de olika materialparen. Med hjälp av undersökningar med profilometer och svepelektronmikroskop (SEM) kunde värden på nötta och vidhäfta volymer erhållas tillsammans med information om nötningssituationer för ytorna mellan de olika materialparen. De nötningsmekanismer som påvisades med hjälp av SEM-undersökningen var adhesiv och abrasiv nötning, och resultaten visade tydligt att nötningen av stålen var omfattande, på grund av att lika material i kontakt med varandra skapar starkare band mellan ytorna, och att de därför inte var en intressant lösning. Det kvävelegerade Vanax 75 uppförde sig visserligen bättre men en tydlig skillnad mot superlegeringarna kunde dock fortfarande konstateras, sett till både friktionskoefficient och mängden slitage. Baserat på dessa resultat valdes Inconel 718 som det bäst lämpade materialet att ersätta de höghaltiga koboltlegeringarna som idag används i ventilen.

The application of the thermally sprayed WC-Co and Cr 3C2-NiCr coatings have been widely used in industry for its superior sliding, abrasive and erosive wear properties. The Al2O3 coating possessing high hardness can be utilized to improve the wear resistance of the metallic surface. Replacing the stamping tool material from steel to lightweight aluminium with protective coatings offers significant gains such as reduction in power costs and increasing operational efficiency during manufacturing of sheet automobile parts. In this study, the WC-CoCr and Cr3C2-NiCr coatings were sprayed with High Velocity Air-Fuel (HVAF) process and Al2O3 coating was deposited using Atmosphere Plasma Spraying (APS) process. The coatings were evaluated and compared based on the results of roughness tests, hardness tests, adhesion tests, quantitative imaging analysis and microstructure analysis. The experimental results revealed that the roughness value varied in a lower range which implies of a high density of the coatings. It was found that coatings have an extremely high hardness value as tested by the Vickers hardness test. The WC-Co coating was found to be the hardest (1215.2HV). The adhesion test was implemented according to the ASTM C633-79 standard. The result showed that WC-Co and Cr3C2-NiCr coatings without a bond coat had high tensile strength, higher than the respective glue strength (63.54MPa, 75.89MPa). Whereas, the Al2O3 coating has a much lower tensile strength (15.2MPa, 25.68MPa, with and without bond) than others and using a bond coat layer does not contribute to an increase in adhesion strength of the cermet coatings. The coating thickness was evaluated using Light Optical Microscopy (LOM) and microstructure analysis was carried out using Scanning Electron Microscopy (SEM). From the microstructure analysis, it was observed that all the coatings have a dense microstructure, very low porosity and low oxide inclusions in top coat. The WC and Cr3C2 grains retain a large volume fraction of finely dispersed in matrix. The alumina coating was found to have low levels of un-melted or the re-solidified particles in the coating. All of the aforementioned analysis and results reveal that WC/CoCr and Cr3C2-NiCr coating show promising potential for press tool applications. However, abrasive resistance test still remained to be done and will be performed in the future. The result of it can reveal the actual wear resistance between two coatings in reality and will be helpful in determining the better protective coating for aluminium press tools

The vision of this thesis is to improve the machinability of workpiece steels. Workpiece material frequently transfers to the cutting tools during machining, and the transfer layers then forming on the tools may give both good and bad effects on machining performance and tool life. The objective of this work is to understand the effects of alloying element additions to workpiece steels on material transfer and the roles of the formed transfer layers on friction characteristics and wear of tools. To isolate and study the influence of the individual alloying elements, model steels are specifically designed. These steels include one reference with C as the only alloying element and others alloyed also with single additions or combined additions of 1 mass% Si, Mn, Cr and Al. The experiments are performed using both a sliding test, simulating the material transfer in milling, and a turning test. In a sliding contact, the mode of transfer is strongly dependent on the normal load and sliding speed. Material transfer initiates extremely fast, in less than 0.025 s, and characteristic transfer layers develop during the first few seconds. The different steel compositions result in the formation of different types of oxides in the transfer layers. At the workpiece/tool interface where the conditions involve high temperature, high pressure and low oxygen supply, easily oxidized alloying elements in the steel are preferentially transferred, enriched and form a stable oxide on the tool surface. The degree of enrichment of the alloying elements in the oxides is strongly related to their tendencies to become oxidized. The difference in melting temperature of the oxides, and thus the tendency to soften during sliding, explains the difference in the resulting friction coefficient. The widest differences in friction coefficients are found between the Si and Al additions. A Si containing oxide shows the lowest friction and an Al containing oxide the highest. The damage mechanism of coated tools is chiefly influenced by the form and shear strength of the transferred material. Absence of transfer layer or non-continuous transferred material leads to continuous wear of the coating. Contrastingly, continuous transfer layers protect it from wear. However, transfer layers with very high shear strength result in high friction heat and a large amount of steel transfer. This leads to rapid coating cracking or adhesive wear.

In the given coating chamber is a system of rotating holders, which holds rotating tools. The chamber also contains electrodes (of various materials), from which the material evaporates and is coating the tools. The goal of this thesis is to simulate the process of coating and visualize the resulting layer in given places of coated tools depending on their placement, number, rotation speed and other optional settings.

>Magister Scientiae - MSc / Photovoltaic (PV) devices based on inorganic-organic hybrid active layers have been extensively studied for over a decade now. However, photoactive hybrid layers of material combinations such as rr-P3HT and SiNWs still require further exploration as candidates for solar cell (SC) fabrication, due to favourable optical absorption and charge carrier mobility associated with them respectively. The ultimate goal of the study is to fabricate ITO/PEDOT:PSS/rr-P3HT:SiNWs/Al SCs with different SiNWs content and investigate the different parameters or factors influencing the performance of these cells. The vertically aligned SiNW arrays on a Si wafer were synthesised via metal assisted chemical etching (MACE) and a method of chemically detaching these wires was developed. The average length and the diameter of the SiNWs obtained were 4.5 μm and 0.2 μm, respectively. Different weight ratios of as-synthesised SiNWs were then incorporated within rr-P3HT to form different hybrid solutions, i.e. rr-P3HT: 0.3 wt% SiNWs, rr-P3HT: 0.7 wt% SiNWs and rr-P3HT: 1.3 wt% SiNWs. In addition, a pure rr- P3HT solution was made for reference purposes. SEM characterisation shows that the SiNWs are randomly distributed across the active area, and that the film becomes progressively inhomogeneous upon addition of SiNWs, whereas the TEM characterisation revealed that there is no chemical interaction between the rr-P3HT and SiNWs. The UV-Vis and PL spectra suggest that there are changes in absorption and emission characteristics upon SiNW incorporation into the rr-P3HT matrix, which may have impacted the charge transfer .The electrical properties of the different hybrid films were probed using Hall Effect measurements, which revealed that the conductivity increases with the increase in the concentration of nanowires (NWs). The increase in conductivity upon the addition of SiNWs in the rr-P3HT matrix was related to an increase of the mobility (μ) of charge carriers in the hybrid films.

[pt] A deposição de parafinas em dutos de produção e coleta é um dos principais problemas de garantia de escoamento na indústria do petróleo. Além das técnicas de prevenção e mitigação tradicionais, o uso de revestimentos internos antiaderentes é uma alternativa ainda em desenvolvimento. Uma extensiva revisão bibliográfica mostrou que muitas das informações disponíveis sobre este assunto baseiam-se em conhecimento de campo e os experimentos desenvolvidos em laboratório apresentam resultados contraditórios. A contribuição deste trabalho foi desenvolver um experimento em laboratório para avaliar a eficiência de superfícies revestidas com relação à prevenção da deposição de parafinas, eliminando o efeito de isolante térmico do mesmo e buscando correlacionar os resultados com as características da superfície como rugosidade, energia crítica e de superfície. O experimento desenvolvido consistia de um loop fechado contendo uma seção de teste em acrílico, com controle de temperatura dos fluidos, medição contínua de fluxo de calor e medição da espessura de depósito através de visualização com câmera. Neste trabalho foram avaliadas as superfícies de aço inox 316L (rugosa e polida), Teflon, Nylon 11 e carbono amorfo sob a forma de placas retangulares que eram acopladas à seção de teste. Os resultados parecem corroborar as conclusões de alguns estudos da literatura, mostrando que a espessura de depósito de parafina pode ser reduzida pela redução da rugosidade e pela redução da energia crítica e de superfície. A utilização da medida de fluxo de calor como medida indireta da espessura de deposição se mostrou promissora, porém a variação da condutividade térmica do depósito em função do número de Reynolds dificulta sua utilização devido à necessidade de calibração para cada vazão de escoamento. / [en] Wax deposition is a relevant flow assurance issue for the petroleum industry. Besides the well-known prevention and mitigation techniques for wax deposition, non-stick internal coatings have been proposed as an alternative solution to this problem. A literature review has been carried out and revealed that the available results, based on either field experience and laboratory experiments, are often contradictory. The present work aims at developing a laboratory apparatus to evaluate the influence of coated surfaces on wax deposition. The experiments were carried out at constant heat flux conditions to eliminate the insulation effects that are associated with the different coating. The tests conducted were aimed at establishing a relationship between wax deposition thickness,, surface roughness and surface energy. The experiments consisted of a closed loop circuit for the wax solution, employing a transparent test section where plates with different surface coatings were tested. Continuous monitoring of the heat flux removed and fluid and plate temperatures allowed total control of the deposition process. Wax layer thicknesses were measured optically with the aid of a digital camera. Five different surfaces were tested, namely, 316L stainless steel (rough and polished), Teflon, Nylon 11 and amorphous carbon. A key finding of these experiments is that the lower the surface energy or the smoother the surface, the lower the wax deposit thickness. However, the wax deposit reduction was seen to be highly dependent on flow conditions. As a side result of the experiments, the indirect determination of wax thickness based on heat flux measurements was shown to be a viable technique. Although the thermal conductivity of the wax deposit, a necessary information for the implementation of the technique, seemed to depend on the flow Reynolds number.