Made available in DSpace on 2014-10-09T12:41:02Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:42Z (GMT). No. of bitstreams: 1 04028.pdf: 4334494 bytes, checksum: 3b9778498dc6bdac0e8a5c8f8ad038da (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Submitted by Alisson Mota (alisson.davidbeckam@gmail.com) on 2015-07-14T19:38:24Z No. of bitstreams: 1 Tese - Ederly Santos Silva.pdf: 1737064 bytes, checksum: 3f36097378fc3cdeb2502d467b6793ac (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2015-07-16T18:26:00Z (GMT) No. of bitstreams: 1 Tese - Ederly Santos Silva.pdf: 1737064 bytes, checksum: 3f36097378fc3cdeb2502d467b6793ac (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2015-07-16T18:30:13Z (GMT) No. of bitstreams: 1 Tese - Ederly Santos Silva.pdf: 1737064 bytes, checksum: 3f36097378fc3cdeb2502d467b6793ac (MD5) / Made available in DSpace on 2015-07-16T18:30:13Z (GMT). No. of bitstreams: 1 Tese - Ederly Santos Silva.pdf: 1737064 bytes, checksum: 3f36097378fc3cdeb2502d467b6793ac (MD5) Previous issue date: 2011-08-01 / FAPEAM - Fundação de Amparo à Pesquisa do Estado do Amazonas / Copaibas are trees that are native to tropics, with nine species found in Brazilian Amazonia. Copaiba trees produce an oil-resin that is found in secretory channels located in the trunks. Copaifera reticulata is the predominant species in the Tapajós National Forest. The socioeconomic aspects of the communities of Pedreira and São Domingos, who are authorized to collect copaiba, and the phytodemographic, genetic and physical-chemical aspects of the copaiba populations available to these communities were analyzed, with the objective of subsidizing future actions of copaiba management in the Tapajós Flona. In the socioeconomic study, semi-structured interviews with the communities extractors elucidated the current local situation with respect to the extraction of copaiba. In the phytodemographic study, the species was identified, the density of potentially productive individuals was quantified, and these were mapped. Microsatellite markers developed by Embrapa Genetic Resources and Biotechnology were used for the genetic analyses. The physical-chemical parameters used were density and viscosity of the oil-resin, as these are associated with potential uses and for the chemical study it was the refraction index, acidity, saponificacion and éster. The management of copaiba is technologically simple, but the extractors identified numerous difficulties, including less advantage in the sale of the oil-resin than formerly, showing that the situation in the past that stimulated them is very different from the current situation, especially in the commercialization process. The density of productive trees in the collection area of Km 67 was 5,5 and of Km 72 was 6,2, with 200 adult individuals geo-referenced. The largest number of productive trees was in the diameter class 51-70 cm, totaling 88 trees, and the largest diameter found was 120 cm. To C. reticulata it presents an oil-resin with viscosity 9 (mPa.s) very variable and it lowers acidity (mg of KOH/g), which could serve as a basis for oil-resin differentiation. With the six microsatellite loci that transferred, 78 alleles were observed. The genetic diversity (He) varied from 0.59 to 0.85 per locus, considered high for Neotropical tree species; however, the observed heterozygosity was smaller than the expected heterozygosity by the Hardy-Weinberg equilibrium in the collection areas, demonstrating a reasonable level of inbreeding (f = 0.375 to 0.419), probably due to a clumped distribution. The analysis with Structure did not identify two populations based on the collection areas, but two genetic groupings based on different combinations of alleles. Most of the genetic variation was found within the collection areas (97%), with weak genetic differentiation among the areas (Fst = 0.030). A little less genetic variation it was found within the genetic groups (93%), with a corresponding increase in divergence (Fst = 0.070). The noncorrespondence between collection areas and genetic groupings could be due to unknown historical events, but, combined with the high genetic diversity founds, suggests that the current levels of inbreeding won't be a problem for a management plan, although the isolation of the Tapajós Flona in the future could contribute to elevate inbreeding to worrying levels. The information presented here will serve as a baseline for future comparison, guiding improvements in the management plan. / As copaíbas são árvores nativas da região tropical das quais nove espécies podem ser encontradas na Amazônia brasileira. As árvores de copaíba produzem um óleo-resina que é encontrado em canais secretores localizados no tronco das árvores. Copaifera reticulata é a espécie predominante na área deste estudo. Foram analisados os aspectos socioeconômicos das Comunidades de Pedreira e São Domingos na Flona do Tapajós, Santarém, Pará, por serem autorizadas a coletar copaíba na Flona, e os aspectos fito-demográficos, genéticos e físicos das populações de copaibeiras disponíveis a estas comunidades, com objetivo de subsidiar futuras ações de manejo de copaíba na Flona. No estudo socioeconômico, realizouse entrevistas semi-estruturadas com os extratores das comunidades para saber a real situação local quanto a extração do produto. No estudo fito-demográfico, identificou-se a espécie, quantificou-se a densidade dos indivíduos que foram potencialmente produtivos, e mapeou-se as árvores. Marcadores microssatélites desenvolvidos pela Embrapa Recursos Genéticos e Biotecnologia serão utilizados para as análises genéticas. Os parâmetros escolhidos para o estudo físico foram a determinação da densidade e viscosidade do óleo-resina por serem relacionados aos usos potenciais, e para o estudo químico foram os índices de refração, acidez, saponificação e éster. O processo de manejo da copaíba apresenta tecnologia simples para a retirada do óleo-resina, mas os extratores apontaram muitas dificuldades em relação ao manejo da espécie. Extrativistas afirmaram que atualmente tem-se menos vantagem na venda do óleo-resina de copaíba do que antigamente, indicando que a situação no passado que os estimulava é bem diferente do quadro atual, necessitando de apoio no processo de comercialização. As densidades dos indivíduos na área de coleta do Km 67 foi 5,5 indivíduos por hectare e no Km 72 foi 6,2 indivíduos por hectare, e 200 indivíduos adultos foram georeferenciados. O maior número de matrizes produtivas encontram-se na classe diamétrica 51-70 cm, totalizando 88 árvores, e o maior diâmetro encontrado foi 120 cm de DAP. A C. 7 reticulata apresenta um óleo-resina com viscosidade (mPa.s) muito variável e baixa acidez (mg de KOH/g), podendo servir de base para diferenciação de óleos-resina. Com os seis locos microssatélites que transferiram foram observados 78 alelos. A diversidade genética (He) variou de 0,59 a 0,85 por locos, considerada alta para a maioria das espécies neotropicais; no entanto, a heterozigosidade observada foi menor que a heterozigosidade esperada pelas proporções do EHW para as áreas de estudo, demonstrando um razoável nível de endogamia (f = 0,375 a 0,419) nas áreas de coleta, provavelmente devido a sua distribuição agrupada. As análises com Structure não identificaram duas populações baseadas nas áreas de coleta, mas sim dois agrupamentos genéticos baseados em conjuntos distintos de alelos. A maior parte da variação genética foi encontrada dentro das áreas de coleta (97%), enquanto encontrou-se uma fraca diferenciação genética entre as áreas (FST = 0,030). Um pouco menos de variação genética foi encontrada dentro dos grupos genéticos (93%), com um aumento correspondente na divergência (FST = 0,070). A não correspondência entre áreas de coleta e agrupamentos genéticos poderia ser devido a eventos históricos desconhecidos, mas, combinada com a alta diversidade encontrada, sugere que a endogamia atual não será um problema para um plano de manejo, embora o isolamento da Flona no futuro poderia contribuir para elevar a endogamia a níveis preocupantes. As informações aqui apresentadas servirão como linha base para comparação futura, orientando melhorias no plano de manejo.

Neste trabalho foram obtidos nanocompósitos de polipropileno (PP) e argilas. Três tipos de PP com índices de fluidez de 1,5; 2,2 e 37,9 g/10min (230ºC/216kg) foram utilizados. O PP com maior índice de fluidez é um produto modificado com peróxido. Essas amostras de PP foram misturadas ao masterbatch da Nanocor nanoMax®-PP. Concentrações de masterbatch variando de 3 a 12% em peso foram utilizadas. Os compósitos foram obtidos em uma extrusora dupla rosca e em um misturador. O Masterbatch foi caracterizado por fluorescência de raios X, difração de raios X (DRX) e por espectroscopia no infravermelho (FTIR). Os compósitos foram caracterizados por DRX, microscopia ótica (MO) e de transmissão (MET), e reologicamente. A caracterização reológica foi realizada conduzindo ensaios de varredura de tempo e ensaios de Cisalhamento Oscilatório de Pequena Amplitude (COPA) no regime de viscoelasticidade linear. Ensaios utilizando uma matriz cônica que permite a avaliação da viscosidade elongacional foram também conduzidos. Com essa matriz foi também possível a avaliação da viscosidade de cisalhamento dos compósitos para taxas de cisalhamento que correspondem a regime de viscoelasticidade linear. Os resultados da caracterização do Masterbatch mostraram que este consiste de uma mistura de polipropileno enxertado com anidrido maleico e uma argila do tipo esmectita, predominantemente montmorilonita (MMT). O espaçamento basal das argilas nos compósitos obtidos foi maior do que aquele da argila no masterbatch para todos os compósitos, diminuindo com o aumento da concentração de masterbatch no compósito. A viscosidade dos compostos obtidos aumentou com o tempo durante os ensaios de varredura de tempo devido a variações morfológicas. Essas variações foram mais importantes quando a freqüência utilizada no ensaio era menor. Essas variações foram correlacionadas com a evolução da morfologia dos compostos em função do tempo. O módulo de armazenamento obtido nos ensaios de COPA a baixas frequências para os compósitos foi maior do que o módulo dos polímeros puros para concentrações de argila acima de 6%. Esse aumento do módulo foi muito mais intenso para o PP de maior índice de fluidez. Os ensaios de caracterização reológica utilizando a matriz cônica mostraram que os nanocompósitos não seguem a Regra de Cox-Merz e que para o PP de maior índice de fluidez a viscosidade elongacional aumenta com o aumento da concentração de masterbatch. / In this work nanocomposites of polypropylene (PP) were obtained. Three types of PP with melt flow rates of 1,5; 2,2 e 37,9 g/10min (230ºC/216kg) were used. The PP with the largest melt flow rate is a product modified with peroxide. These samples were mixed with PP masterbatch Nanocor nanoMax ®-PP. Masterbatch in different concentrations ranging from 3 to 12 wt%. The composites were obtained using a twin screw extruder and internal mixer. The masterbatch was characterized by X-ray fluorescence, X-ray diffraction (XRD) and infrared spectroscopy (FTIR). The composites were characterized by XRD, optical microscopy (OM) and transmission (TEM) and rheologically. The rheological characterization was made carrying out time sweep, small amplitude oscillatory shear (SAOS) tests in order to study the rheological behavior on the linear viscoelastic regime. Tests using a conical diewith which it is possible to measure elongational viscosity were also conducted. The shear viscosity at high shear rates was evaluated using a slit die The characterization results showed that the masterbatch is a mixture of polypropylene grafted with maleic anhydride and a smectite type clay, predominantly montmorillonite (MMT). The basal spacing of clay in the composites was greater than that of the clay within the masterbatch for every composites. It was shown to decrease with increasing concentration of masterbatch in the composite. The viscosity of composites increased during the time sweep experiments. This evolution of viscosity was attributed to changes of morphology of the composites. These variations were more important when the frequency used in the test was lower. The storage modulus obtained during COPA at low frequencies for composites was higher than the modulus of the pure polymers when the clay content was above 6%. This increase in modulus was greater for the lower melt flow index PP The rheological tests performed using the slit die showed that Cox-Merz rule was not valid for the composites. The elongational viscosity was shown to increase with increasing concentration of masterbatch.

Orientador: Antonio Carlos Bannwart / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica e Instituto de Geociências / Made available in DSpace on 2018-08-21T10:26:56Z (GMT). No. of bitstreams: 1 Badin_CarolineMarques_M.pdf: 3397830 bytes, checksum: 988506c836c8d44fcf606acc8357efab (MD5) Previous issue date: 2012 / Resumo: Uma das principais características das parafinas de alto peso molecular é a sua baixa solubilidade na maioria dos solventes de bases parafínicas, aromáticas, naftênicas e outros solventes oleosos, quando em temperatura ambiente. Entretanto, nas condições de reservatório em que se encontram, a solubilidade destes componentes é suficientemente alta para manter todas as moléculas devidamente dissolvidas na mistura óleo/parafina. Quando se inicia um processo de extração, o óleo explotado experimenta uma variação brusca de temperatura e pressão, o que acaba afetando de modo significativo a reologia de um óleo parafínico. Portanto, conhecer o comportamento reológico desses óleos é importante para o estudo da repartida de linhas bloqueadas devido à gelificação, que pode ocorrer durante processos de parada das linhas submarinas de produção, seja por etapas do processo ou de manutenção. O presente trabalho tem como objetivo estudar o comportamento físico-químico e reológico de um óleo parafínico, submetendo-o a baixas temperaturas e, assim, simulando a formação dos géis nas linhas. Os testes reológicos foram realizados em um reômetro Mars III, numa faixa de temperatura entre 50 a 5°C. As análises físico-químicas têm como objetivo estudar as características básicas do óleo parafínico como, por exemplo, densidade e composição. Os resultados reológicos mostram que o fluido, apesar da pouca quantidade de parafina, apresenta um aumento significativo na sua viscosidade durante um processo de resfriamento e uma gelificação considerável ocorre. Como a gelificação se deve ao aparecimento de cristais de parafina, a temperatura de cristalização da mesma (TIAC) foi determinada através da análise da variação da viscosidade com o decréscimo de temperatura bem como por DSC. Além disso, o ponto onde o fluido gelificado deixa de fluir, devido ao excesso de cristais presentes e alta viscosidade, foi determinado através de análises oscilatórias. Como o fluido acaba gelificando, se faz necessário determinar uma tensão mínima de escoamento, para que o fluido volte a escoar, e a mesma foi determinada através dos métodos de análise de aplicação de tensão estática e oscilatória / Abstract: One of the main characteristics of high molecular weight paraffins is its low solubility in most solvents with paraffin, aromatic or naphthenic base and also other oily solvents, when at room temperature. However, at reservoir conditions in which they can be found, the solubility of these components is high enough to keep all molecules fully dissolved in the mixture oil / paraffin. When one starts a process of extraction, the exploited oil experiences a sudden change on temperature and pressure, thus affecting significantly the rheology of a paraffinic oil. Therefore, knowing the rheological behavior of these oils is important to study the restart of blocked lines due to gelation, which can occur during the process of shutdown of the production subsea lines, either for maintenance or emergency reasons. The present work aims to study the physical-chemical and rheological behavior of a paraffinic oil, subjecting it to low temperatures and thus simulating the formation of gels inside the lines. The rheological tests were performed on a rheometer Mars III, in a temperature range of 50 to 5 ° C. The physical-chemical analysis have the aim to study the basic features of a paraffin oil, as for example, density and composition. The rheological results shows that the fluid, despite of the small amount of paraffin, presents a significant increase in viscosity during a cooling process and a considerable gelification occurs. As the gelification is due to the appearance of paraffin crystals inside the oil, the wax appearance temperature (WAT) was determined by analyzing the change in viscosity with a decreasing temperature. Moreover, the point where the gelled fluid stops flowing, due to excessive number of crystal and also high viscosity, was determined by oscillatory tests. Because the fluid gels inside of the pipeline, it is necessary to determine a minimum yield stress, for the fluid restart the flow, and this was determined using the methods of analysis of the application of static and oscillatory tension / Mestrado / Explotação / Mestra em Ciências e Engenharia de Petróleo

In recent years drilled shafts have become the preferred foundation method for marine bridges. Typically, the drilled shaft is selected over traditional driven piles due to soil strata encountered, construction economy, increased lateral stiffness requirements, and/or vibration control considerations. The most critical component in drilled shaft construction is borehole stabilization. Wall sloughing or groundwater inclusion can have devastating effects on the strength of the finished shaft however recent research has shown that the materials, more specifically the slurry, used to accomplish stabilization may be having a negative impact on the durability of the finished product. This thesis investigates the durability of drilled shaft specimens as it relates to the slurry type and viscosity. Electrochemical corrosion potential test results from 23 lab cast specimens showed that the shafts cast using bentonite slurry were 54% more likely to exhibit corrosion potential crossing the ASTM threshold of -350mV. The laboratory setting allowed for visual inspection of each shaft. This inspection showed reflective quilting on all bentonite cast shafts, this quilting was visible to a lesser degree on select polymer cast shafts and not present on shafts cast in water. This creasing appears to be directly related to the slurry used and the resulting decrease in durability. While current construction practice favors the use of bentonite slurry, the study indicates that both polymer slurry and the casing method are more advantageous from a durability standpoint.

The aim of this study was to determine the influence of alumina increase on the functioning of casting powder during continuous casting. Two aspects of the powder's performance were experimentally measured, namely the influence of alumina on the viscosity and the crystallisation behaviour. These two aspects were then related to the in-mould functioning of the casting powder with the aid of literature references. Casting slag must provide lubrication between the mould surface and the thin steel shell. Alumina increase will cause viscosity increase in casting slags and will hinder lubrication when the inflow of casting slag into the mould/strand gap deteriorates. Heat transfer across the gap is determined by the amount of solid casting slag and the form (glass or crystalline) thereof. Heat transfer across a crystalline material may be up to seven times lower than that across a glass phase. The increased alumina will serve to increase the ratio of glassy phase to crystalline phase in the gap, so increasing the heat transfer. To determine the true extent of alumina increase with modern clean steel practice, samples were taken from the moulds of both the VI and V2 continuous casters at ISCOR Vanderbijlpark. The influence of this alumina increase on the viscosity and the crystallisation behaviour of the casting slag were experimentally measured. Viscosity measurements were done with a rotating bob viscometer (in a vertical tube furnace) on two commercial casting powders (with increasing AI2O3 content). Viscosity prediction models were evaluated with the data from the measured viscosity values. Crystallisation measurements were done by quench experiments with the aid of the hot thermocouple technique. Crystallisation behaviour after a specified heat cycle was presented as the percentage opaque material (crystalline) to vitreous material (glassy) measured with an optical microscope. For the seven sequence casts during which samples were collected from the mould, it was found that the alumina content of the casting slag reached a steady-state value within the first ladle (first 40 minutes) with an increase of 3 to 4 mass %. The influence of a 4 mass % alumina increase on the measured viscosity is small enough that proper lubrication function of the slag will not be negatively affected. Viscosity prediction models vary in their accuracy and are limited with respect to the composition range of the casting powder and the temperature range for which they are valid. The increased alumina content was found to have a strong influence on the percentage crystalline material present. After the sample was heated to 1300°C, kept there for 10s, and then quenched, the crystalline material will decrease from 60 % to 30 % for 5 mass % alumina added. This decreased crystalline material present may notably increase heat transfer. Full crystallisation does not occur at a single temperature, and crystallisation occurs over a temperature interval (of up to 200°C). This means that crystallisation temperature values quoted by casting powder manufacturers depend on the heat cycle and the technique used during crystallisation measurements. Several crystalline phases are usually present in solidified casting slag and these crystalline phases are strongly influenced by the alumina content: the stable crystalline phases may change as alumina content increases. For the current alumina increase in casting powders the effect on viscosity is small, while crystallisation behaviour may be influenced to a greater extent. / Dissertation (M Eng (Metallurgical Engineering))--University of Pretoria, 2006. / Materials Science and Metallurgical Engineering / unrestricted

No description available.

This thesis focuses on how the properties of polymer thin films depend on the film thickness and molecular weight (Mw). Previous studies of polystyrene (PS) films coated on silica with Mw of 2.4 and 212 kg/mol found that the viscosity of the films decreases with decreasing film thickness. A two-layer model assuming a 3 nm thick mobile layer situated at the top surface of the film and hydrodynamically coupled to a bulklike inner layer is able to describe the viscosity of the films. To better understand the dynamics exhibited by the surface mobile layer, this work extends the measurement to various other Mw up to 2316 kg/mol. The result shows that the viscosity of the films also decreases with decreasing film thickness and can be described by the same two-layer model. But there are exceptional findings as well. Specifically, the viscosity of the high-Mw films (> 60 kg/mol) exhibit a Mw^0 dependence, distinctly different from the Mw^3.4 dependence exhibited by the viscosity of the bulk polymer. Moreover, the surface chains in the high-Mw films, as inferred from the two-layer model, are in an unphysically stretched state. These observations led to the conjecture that the viscosity reduction in the high-Mw films is due to a different mechanism from that in the lower Mw films which is directly tied to the surface mobile layer as in the two-layer model. To scrutinize this conjecture, viscosity measurement is extended to PS films doped with Dioctyl phthalate (DOP). A previous experiment showed that the influence of the surface on the overall dynamics in this system is likely to be much smaller than in the undoped films. The measurement results are examined to determine, among other things, whether the viscosity reduction relative to that in the undoped films is weaker in the low-Mw than in the high-Mw regime.

Thesis advisor: Kevin S. Bedell / One of the many achievements of renowned physicist L.D. Landau was the formulation of Fermi Liquid Theory (FLT). Originally debuted in the 1950s, FLT has seen abundant success in understanding degenerate Fermi systems and is still used today when trying to understand the physics of a new interacting Fermi system. Of its many advantages, FLT excels in explaining why interacting Fermi systems behave like their non-interacting counterparts, and understanding transport phenomena without cumbersome and confusing mathematics. In this work, FLT is applied to systems whose low energy excitations obey the massless Dirac equation; i.e. the energy dispersion is linear in momentum, ε α ρ, as opposed to the normal quadratic, ε α ρ². Such behavior is seen in numerous, seemingly unrelated, materials including graphene, high T[subscript]c superconductors, Weyl semimetals, etc. While each of these materials possesses its own unique properties, it is their low energy behavior that provides the justification for their grouping into one family of materials called Dirac materials (DM). As will be shown, the linear spectrum and massless behavior leads to profound differences from the normal Fermi liquid behavior in both equilibrium and transport phenomena. For example, with mass having no meaning, we see the usual effective mass relation from FLT being replaced by an effective velocity ratio. Additionally, as FLT in d=2 has been poorly studied in the past, and since the most famous DM in graphene is a d=2 system, a thorough analysis of FLT in d=2 is presented. This reduced dimensionality leads to substantial differences including undamped collective modes and altered quasiparticle lifetime. In chapter 3, we apply the Virial theorem to DM and obtain an expression for the total average ground state energy $E=\frac{B}{r_s}$ where $B$ is a constant independent of density and $r_s$ is a dimensionless parameter related to the density of the system: the interparticle spacing $r$ is related to $r_s$ through $r=ar_s$ where $a$ is a characterstic length of the system (for example, in graphene, $a=1.42$ \AA). The expression derived for $E$ is unusual in that it's typically impossible to obtain a closed form for the energy with all interactions included. Additionally, the result allows for easy calculation of various thermodynamic quantities such as the compressibility and chemical potential. From there, we use the Fermi liquid results from the previous chapter and obtain an expression for $B$ in terms of constants and Fermi liquid parameters $F_0^s$ and $F_1^s$. When combined with experimental results for the compressibility, we find that the Fermi liquid parameters are density independent implying a unitary like behavior for DM. In chapter 4, we discuss the alleged universal KSS lower bound in DM. The bound, $\frac{\eta}{s}\geq\frac{\hbar}{4\pi k_B}$, was derived from high energy/string theory considerations and was conjectured to be obeyed by all quantum liquids regardless of density. The bound provides information on the interactions in the quantum liquid being studied and equality indicates a nearly perfect quantum fluid. Since its birth, the bound has been highly studied in various systems, mathematically broken, and poorly experimented on due to the difficult nature of measuring viscosity. First, we provide the first physical example of violation by showing $\frac{\eta}{s}\rightarrow 0$ as $T\rightarrow T_c$ in a unitary Fermi gas. Next, we determine the bound in DM in d=2,3 and show unusual behavior that isn't seen when the bound is calculated for normal Fermi systems. Finally we conclude in chapter 5 and discuss the outlook and other avenues to explore in DM. Specifically, it must be pointed out that the physics of what happens near charge neutrality in DM is still poorly understood. Our work in understanding the Fermi liquid state in DM is necessary in understanding DM as a whole. Such a task is crucial when we consider the potential in DM, experimentally, technologically, and purely for our understanding. / Thesis (PhD) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

The ability of a lubricating oil to reduce friction in mechanical surfaces which are in relative sliding motion depends on the base oil behaviour. Previous studies have demonstrated that temperature has a significant influence on the friction behaviour of mineral and synthetic base oils by using a laboratory based friction testing machine. However, the effect of a constantly changing load under different temperature conditions has not been explored fully. In this study, the effect of an increasing load on the friction behaviour of four six different mineral base oils and a polyalphaolefin (PAO) base oil were studied using the SRV4® tribometer. The sliding surfaces were AISI 52100 steel ball and disc. The average loads (range: 50 – 250 N), temperatures (range: 40 – 120 oC), relative humidity of 20 % and a sliding speed of 0.2 m.s-1 were selected as the test conditions. The seven base oils were selected from four API base oil groups. Stribeck curves were used as a tool to characterize the friction behaviour of the base oils. The results show that for all the base oils, the coefficient of friction and the Stribeck parameter decrease gradually with the increase in applied normal load under constant temperature conditions. The increase in temperature increased the coefficient of friction and decreased the Stribeck parameter at each load stage. The external friction mechanisms dominated the friction behaviour under all test conditions. Viscosity showed a strong influence on the film forming characteristics of the seven base oils only at 40 and 60 oC. Between 80 and 120 oC, the oil-surface interactions were predominant. The results further demonstrated that effect of an increasing temperature on the coefficient of friction was bigger between 80 and 100 oC for all Group III base oils and was consistent between 40 and 120 oC for the Group III+ and PAO base oil. The highly saturated (PAO and Group III+) base oils have demonstrated good thermal stability and less reactivity compared to the less saturated base oils (GI and GIII) under all test conditions. The friction behaviour of the PAO base oil was the most affected by the presence of dissolved water. The presence of water proved to increase the friction at the sliding steel interfaces. / Dissertation (MEng)--University of Pretoria, 2018. / Chemical Engineering / MEng / Unrestricted