Properties of both chemical contaminants and polymers can impact contaminant diffusivity and solubility in new and aged polyethylene materials for pipes and geomembranes. Diffusivity, solubility, polymer and chemical properties were measured for thirteen contaminants and six polyethylene materials that were new and/or aged in chlorinated water. Tree regression was used to select variables, and linear regression was used to develop predictive equations for contaminant diffusivity and solubility in polyethylene. Organic contaminant properties had greater predictive capability than polyethylene properties. Model coefficients significantly changed between new materials to chlorine-aged materials, indicating changes of polyethylene properties impact the interaction between contaminants and polymers. The metallic flavor of copper in drinking water influences the taste of water and can cause the taste problems for water utilities. The mechanism of metallic flavor caused by these metals is related to free or soluble ions. Free copper concentrations were measured at different pH in diluted artificial saliva using a cupric ion selective electrode. Three major proteins in human saliva: α-amylase, mucin and lactoferrin, were added in the artificial saliva and the impacts on the chemical speciation of copper were analyzed. Inorganic saliva components, typically phosphate, carbonate and hydroxide combined with copper and greatly influenced the levels of free copper in the oral cavity. Proteins such as α-amylase, mucin and lactoferrin also impacted the chemical speciation of copper, with different affinity to copper. Mucin had the greatest affinity with copper than α-amylase. / Master of Science

Soilless substrates, such as peat, pine bark, and coir, are widely used as growing media in containerized crops for their favorable characteristics, including low bulk density, balanced air exchange and water retention, disease resistance, and low pH and salinity. However, improper irrigation of these media can have negative outcomes such as root asphyxia, pathogen development, and reduced plant growth. Understanding pore size distributions, water dynamics, and gas diffusivity of these substrates is essential to promote plant growth. The effects of different particle sizes of soilless media on processes such as infiltration, hydraulic conductivity, and gas diffusivity are also not well understood. The characterization of these effects is important for the overall improvement of container crop production. This thesis presents three studies that aimed to characterize the physical and hydraulic properties of pine bark substrates, both unamended and amended with peat or coir. The first study looked at three substrate types: unamended, unscreened pine bark, peat-amended pine bark, and coir amended pine bark. Three methods were employed to quantify pore distributions: non-equilibrium infiltration measurements, equilibrium water retention characterization, and scanning electron microscopy. We characterized pore distributions during wetting and drainage for the three substrates. Coir-amended bark had the largest water-conducting porosity, highest hydraulic conductivity, and most water retention. Unamended pine bark had the highest microporosity, and the addition of peat and coir lowered macroporosity, with peat having the greater effect. The total porosity inferred from the infiltration method was significantly smaller than that inferred from drainage experiments due to assumptions related to pore shape. The second study focused on defining hydraulic conductivity and water retention for pine bark substrates of five different particle sizes, <1 mm, 1-2 mm, 2-4 mm, 4-6 mm, and an unscreened fraction. We utilized the same methods from the first study. The resulting data showed that the smallest particle sizes (i.e., <1 mm and 1-2 mm) had the highest hydraulic conductivity and greatest water retention. The three larger sizes had lower hydraulic conductivity and poor water retention, including the unscreened fraction, which more closely followed the results of the 2-4 mm size. The final study examined gas diffusivity of the five pine bark particle sizes at different moisture levels: 60% moisture content (initial conditions), saturated at the bottom of the sample, near-saturated at the sample bottom, and drained from saturation to container capacity. We used a one-chamber gas diffusion setup to find gas diffusion coefficients (Ds). The results displayed an inverse relationship between Ds values and substrate water content. In addition, the larger particle sizes were less sensitive to changes in water content due to their well-draining large pores. Proper balance of aeration and water retention is necessary for the success of soilless growing media. Overall, the smaller particle size fractions had the best water retention and hydraulic conductivity rates while the larger fractions had the largest Ds coefficients. This work contributes valuable knowledge on the physical and hydraulic properties of different size fractions of pine bark substrates, which can assist nursery growers in optimizing water usage for sustainable container crop production. / Master of Science / Since the 1950's soilless substrates have been an important resource for growing a variety of fruits, vegetables, flowers, and ornamental plants. Soilless growing media have become more popular choices for containerized plant production compared to natural soils due to improved air exchange, increased disease resistance, and more plants per acre. They are also favored because they help conserve resources, reduce agricultural waste, and minimize transportation requirements as compared to traditional cropping methods. The most popular types of soilless media include peat, coir, compost, and pine bark. In the U.S., pine bark is the main substrate used, as it is renewable and widely available. Growers still face many issues when using containerized crop production. For example, pine bark is susceptible to water runoff which can cause environmental problems and increase costs from this loss of water and fertilizer. Further characterizing of water and gas dynamics in of pine bark growing media is important for conserving water and fertilizer resources while optimizing plant growth in this container cropping industry. Pore characteristics, aeration, and water movement are key factors of substrates to be described to solve these challenges. This project aimed to apply soil physics strategies to soilless media, focusing on describing pore sizes, water movement, water holding capacity, and air movement in pine bark substrates. We utilized three methods throughout this study. For the first method, we took infiltration measurements to examine how water moved into the media, while the second utilized controlled drainage experiments to observe how water moved out of the media. The final method was characterizing gas movement through the substrates at different water contents and particle sizes. The results found showed that the smaller particle sizes and pine bark mixed with peat and coir had increased ability to retain water and allow water movement as compared to the larger particle sizes and unamended pine bark. In contrast, the larger particles had less water retention but improved gas movement. These results could be applied by stacking different particle sizes or mixes over one another could optimize water retention in the top of the container and drainage and gas movement in the bottom of the container. Overall, the application of this work is to create best management practices for growers to be able to balance water retention and gas movement in order to optimize plant growth.

This thesis documents research done in the development and the exploration of feasibility for a high-throughput method to measure local thermal properties. The present capabilities in the measurement of local thermophysical properties such as thermal conductivity, thermal diffusivity, and Kapitza resistance are very inefficient and impractical to fully understand and characterize heat transport through certain materials and features. This work follows up on past work in local thermal property measurement via the spatial domain thermoreflectance (SDTR) method, and explores the possibility of parallelizing the process. The parallelized SDTR (P-SDTR) method involves using laser projector sources to periodically heat and measure the changes of reflectivity of a sample surface at multiple locations simultaneously. These measurements are made possible by the development of a lock-in camera that can measure the characteristics of modulated light using lock-in amplification at several spots across an area with an advanced camera sensor. This method allows for the measurement of local thermal properties across features such as grain boundaries, or directional properties in anisotropic materials. An experimental setup is developed to determine at which heating and probing parameters a thermoreflectance signal can be measured. A finite element model is also made to simulate the P-SDTR process, and validate that the assumptions made in SDTR can be made in P-SDTR measurements. It is shown that at an appropriate separation of heating/measurement locations, the solutions from the simulation approach that of a single measurement spot. An initial device design is proposed and tested. Future work in the development of the P-SDTR device is also laid out.

Master of Science / Department of Civil Engineering / Kyle Riding / Corrosion of reinforcing steel is one of the most common and serious causes of reinforced concrete deterioration. While corrosion is normally inhibited by a passive layer that develops around the reinforcing steel due to the high pH environment of the surrounding concrete, chlorides will break down this protective layer, leading to reinforcement corrosion. Decreasing the diffusivity of the concrete would slow the ingress of chlorides into concrete, and is one of the most economical ways to increase the concrete service life. Optimized concrete mixtures blending portland cement and supplementary cementing materials (SCMs) have become popular throughout the construction industry as a method of improving both fresh and long-term concrete properties such as workability, strength and porosity. It has been shown that use of Class F fly ash, silica fume and ground granulated blast furnace slag (GGBFS) in binary concrete mixture blends can result in a significant reduction in concrete diffusivity. This study investigates the ability of Class C fly ash and ternary concrete mixture blends to also aid in diffusivity reduction. In order to study the effect of incorporation of SCMs into concrete, mixtures containing Class C and Class F fly ash, silica fume and GGBFS were tested following the ASTM C 1556 procedures to measure the concrete’s apparent chloride diffusivity. Structure life cycles were modeled using the measured apparent chloride diffusivities with two finite-difference based life-cycle analysis software packages. To determine whether a correlation between diffusivity and deterioration due to freezing and thawing exists, samples were also tested for their ability to resist deterioration from freezing and thawing cycles using a modified ASTM C 666 Procedure B test. Results show that the use of Class C fly ash yields some service life improvements as compared to the portland cement control mixtures, while ternary mixture blends performed significantly better than the control mixture and equal to or better than the binary SCM mixtures tested. Freeze-thaw tests showed all mixtures to be equally resistant to deterioration due to freezing and thawing.

Unlike thin tissues (e.g., skin) which has been successfully grown, growing thick tissues (e.g., bone and muscle) still exhibit certain limitations due to lack of nutrients (e.g., glucose and oxygen) feeding on cells in extracapillary space (ECS) region, or also known as scaffold in an in vitro static culture. The transport of glucose and oxygen into the cells is depended solely on diffusion process which results in a condition where the cells are deprived of adequate glucose and oxygen supply. This condition is termed as hypoxia and leads to premature cell death. Hollow fibre membrane bioreactors (HFMBs) which operate under perfusive cell culture conditions, have been attempted to reduce the diffusion limitation problem. However, direct sampling of glucose and oxygen is almost impossible; hence noninvasive methods (e.g., mathematical models) have been developed in the past. These models have defined that the glucose diffusivity in cell culture medium (CCM) is similar to the diffusivity in water; thus, they do not represent precisely the nutrient transport processes occurring inside the HFMB. In this research, we define glucose as our nutrient specie due to its limited published information with regard to its diffusivity values, especially one that corresponds to cell/tissue engineering (TE) experiments. A series of well-defined diffusion experiments are carried out with TE materials of varying pore size and shapes imbibed in water and CCM, namely, cellulose nitrate (CN) membrane, polyvinylidene fluoride (PVDF) membrane, poly(L-lactide) (PLLA) scaffold, poly(caprolactone) (PCL) scaffold and collagen scaffold. A diffusion cell is constructed to study the diffusion of glucose across these materials. The glucose diffusion across cell-free membranes and scaffolds is investigated first where pore size distribution, porosity and tortuosity are determined and correlated to the effective diffusivity. As expected, the effective diffusivity increases correspondingly with the pore size of the materials. We also observe that the effective glucose diffusivity through the pores of these materials in CCM is smaller than in water. Next, we seeded human osteoblast cells (HOSTE85) on the scaffolds for a culture period of up to 3 weeks. Similar to the first series of the diffusion experiments, we have attempted to determine the effective glucose diffusivity through the pores of the scaffolds where cells have grown at 37°C. The results show that cell growth changes the morphological structure of the scaffolds, reducing the effective pore space which leads to reduced effective diffusivity. In addition, the self-diffusion of glucose in CCM and water has also been determined using a diaphragm cell method (DCM). The results have shown that the glucose diffusivity in CCM has significantly reduced in comparison to the water diffusivity which is due to the larger dynamic viscosity of CCM. The presence of other components and difference in fluid properties of CCM may also contribute to the decrease. We finally employ our experimentally deduced effective diffusivity and self-diffusivity values into a mathematical model based on the Krogh cylinder assumption. The glucose concentration is predicted to be the lowest near the bioreactor outlet, or in the scaffold region, hence this region becomes a location of interest. The governing transport equations are non-dimensionalised and solved numerically. The results shown offer an insight into pointing out the important parameters that should be considered when one wishes to develop and optimise the HFMB design.

Made available in DSpace on 2017-07-21T19:25:50Z (GMT). No. of bitstreams: 1 Aloisi Somer2.pdf: 7687974 bytes, checksum: 2416565c5d4c2106a977eae2ad58cbfe (MD5) Previous issue date: 2016-02-19 / Fundação Araucária de Apoio ao Desenvolvimento Científico e Tecnológico do Paraná / The generation of mechanical waves can be produced in the air in contact with the surface of a sample since a modulated light focus on that sample. This feature is well known, and there are several techniques and theoretical models to elucidate this process. One of the techniques used to measure such waves is the technique of cell Open Photoacoustic (OPC), and why it is can estimate the thermal diffusivity of a sample. The hypothesis in this thesis is that small structural changes in thin superficial layers can influence on effective thermal diffusivity measured by the OPC technique. Initially, it was carried out a review of mathematical models presented in the literature for samples with double layer, and the approach of a second thin layer. It has been found that the influence of a thin layer on a thick sample is negligible, and, therefore, the effective thermal diffusivity tends to the value of the thermal diffusivity of the bulk sample in all models. To check the influence of structural modification in a second thin layer were produced two sets of samples with two kinds of surface structural changes in samples with metallic volume. The first set was with changes in the proportions of rutile and anatase, the structural phases TiO2 film which was grown by thermal oxidation treatment in three types of titanium metal: two degrees of purity titanium, Ti and TiG2, and a TiG5 alloy (Ti-6Al-4V). The correlation of effective thermal diffusivity and the structural modification of layers grown by different thermal treatment (at 600 and 700ºC) in various treatment times was established. The effective thermal diffusivity determined by OPC is directly proportional to anatase quantity in the thermally grown layer of samples. In the second set were created different concentrations of structural martensite phase by mechanical polishing of austenitic AISI304 steel samples, having an austenitic volume. The effective thermal diffusivity values are influenced as the ratio martensite/austenite as the thickness of the sample. It was expected a decrease in effective thermal diffusivity values with decreasing the martensite quantity on the surface of samples as with the increase in the thickness of samples. This behavior was partially observed, however for small proportions of martensite and higher thickness values the effective thermal diffusivity increases. This feature can be associated with non-linear effects. Also, a method to check the thermal diffusivity values obtained by the OPC technique was proposed. This procedure comes from the dependency of the weight parameter thermoelastic bending C2, which depends on the thickness of the sample. If the dependence of C2 is as close to ls-3 confirms the values of thermal diffusivity. The method was tested for aluminum samples successfully. In conclusion, the variation in concentration of structural changes on sample´s surface and thin layers can influence the effective thermal diffusivity obtained by OPC technique, contrary to the theoretical models predict. / A geração de ondas mecânicas pode ser produzida no ar em contato com a superfície de uma amostra desde que sobre a mesma incida uma luz modulada. Isso já é bem conhecido e existem várias técnicas e modelos para elucidar tal processo. Uma das técnicas utilizadas na mensuração de tais ondas é a técnica de Célula Fotoacústica Aberta (OPC – Open Photoacoustic Cell), pela qual é possível estimar a difusividade térmica de uma amostra. A hipótese levantada nesta tese é que pequenas modificações estruturais em finas camadas superficiais possam influenciar a difusividade térmica efetiva mensurada pela técnica OPC. Inicialmente foi realizada uma revisão bibliográfica dos modelos matemáticos para amostras com dupla camada, e para a aproximação de uma segunda camada muito fina. Foi verificado que a influência de uma fina camada sobre uma amostra espessa é desprezível, e consequentemente, a difusividade térmica efetiva tende ao valor da difusividade térmica do volume da amostra, em todos os modelos. Para verificar a influência de uma modificação estrutural em uma segunda camada muito fina foram produzidos dois conjuntos de amostras, com dois tipos de modificações estruturais superficiais em amostras metálicas. O primeiro conjunto com alterações das proporções entre rutilo e anatásio, fases estruturais do filme de TiO2, que foi crescido por meio de tratamento de oxidação térmico um volume de titânio metálico para três tipos deste metal: dois graus de pureza de titânio, Ti e TiG2, e uma liga TiG5 (Ti-6Al-4V). A correlação de difusividade térmica e a microestrutura das camadas crescidas por tratamento de oxidação térmico sobre Ti, TiG2 e TiG5 a 600 ºC e 700 ºC, em diferentes tempos foi estabelecida. Observou-se que a difusividade térmica efetiva medida pela técnica OPC é diretamente proporcional a quantidade de anatásio na camada criada por tratamento térmico. No segundo conjunto foram criadas diferentes concentrações da fase estrutural martensita por polimento mecânico em amostras de aço austenítico AISI304, que possui um volume austenítico. Foi observado que a difusividade térmica efetiva teve influência tanto da razão martenstia/austenita quanto da espessura do volume da amostra. Esperava-se uma diminuição da difusividade térmica efetiva com a redução da quantidade de martensita na superfície e com o aumento da espessura do volume da amostra. Esse comportamento foi parcialmente observado, mas para pequenas proporções de martensita e maiores espessuras a difusividade térmica efetiva tornou a aumentar. Comportamento que pode ser associado a possíveis efeitos não lineares. Ainda, foi proposto um método de confirmação para os valores da difusividade térmica medida pela técnica OPC. Esse método parte da dependência do parâmetro peso da flexão termoelástica C2, o qual depende da espessura da amostra. Quando a dependência medida para o parâmetro C2 estiver próxima ls-3 confirma-se os valores da difusividade térmica. O método foi testado para amostras de alumino com êxito. Em conclusão é constatado que modificações na concentração da fase estrutural na superfície e em finas camadas têm influência na difusividade térmica efetiva medida pela técnica OPC, ao contrário do constatado pelos modelos teóricos presentes na literatura.

Made available in DSpace on 2017-07-21T19:26:02Z (GMT). No. of bitstreams: 1 Ricardo Oyarzabal.pdf: 3669233 bytes, checksum: 4e83f2e83bacb45a6f0ae5f95c2dfa29 (MD5) Previous issue date: 2012-03-22 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / The photoacoustic technique is a method used in the study of physical and thermal properties of solids, liquids or gases and it is based on the photothermal effect. The photothermal effect results from the combination of physical mechanisms such as thermal expansion, thermal diffusion and thermoelastic bending. Thermal diffusivity is a parameter that measures how much heat is diffused over a sample and depends on the thermal conductivity k, density ρ and specific heat c of the material under analysis. For this study, we used the open cell photoacoustic (OPC) technique to measure the thermal diffusivity of samples of AISI 316 steel. The standard sample has a thickness of 490 micron and a diameter of 31.73 mm as the others received coatings by plasma treatment nitrocarburizing. This process of ion implantation modifies the tribological properties and mechanical characteristics of the region around the surface of a material, as different precipitates are formed, thus changing the thermal diffusivity. In this investigation we divided the samples into three distinct regions, and the area A in the center, an intermediate region B and C is the region most extreme. The theoretical value of diffusivity for the steel AISI 316 is 4.05 x10-6 m2/s. Through the OPC technique the results for each region were: αA = 4.08 x10-6 ± 0,18 m2/s, αB = 4.09 x 10-6 ± 0,12 m2/s , αC = 4.09 x 10-6 ± 0,22 m2/s. These results are close to theoretical values and show that the thermal diffusivity does not radially change from the center to the edge of the sample. For the nitrocarburized samples with circular, circular center hole, triangular and square geometries it was observed, by optical microscopy and thermal diffusivity determination, that the nitrocarburizing is not uniform across the surface of the sample and varies according to its region, with greater intensity at the edges than the center. Thus, OPC is a technique sensitive to the structural changes at surfaces of a bulk so that can be used to distinguish surfaces that have suffered or not nitrocarburizin. / A técnica fotoacústica é um método utilizado no estudo de propriedades físicas e térmicas de materiais sólidos, líquidos ou gasosos, com base no efeito fototérmico. O fenômeno fototérmico resulta da combinação de mecanismos físicos como a expansão térmica, difusão térmica e a flexão termoelástica. A difusividade térmica é um parâmetro que mede quanto o calor é difundido ao longo de uma amostra e depende da condutividade térmica k, da densidade ρ, e do calor específico c do material em análise. Para realização deste trabalho utilizou-se o sistema de Fotoacústica em Célula Aberta (OPC) para a medida da difusividade térmica de amostras do aço AISI 316. A amostra padrão possui espessura de 490 μm e diâmetro de 31,73 mm e nas outras houve a produção de camadas superficiais pelo tratamento de nitrocementação por plasma. Este processo de implantação iônica modifica as propriedades tribológicas e mecânicas da região em torno da superfície de um material, pois diferentes precipitados são formados, alterando assim a difusividade térmica. Nesta investigação dividiu-se as amostras em três regiões distintas, sendo a região A no centro, B uma região intermediária e C a região mais extrema. O valor teórico da difusividade para o aço AISI 316 é 4,05 x10-6 m2/s. Através da medida em OPC os resultados obtidos para cada região na amostra padrão foram: αA = 4,08 x10-6 ± 0,18 m2/s, αB = 4,09 x 10-6 ± 0,11 m2/s, αC = 4,09 x 10-6 ± 0,21 m2/s. Estes resultados são próximos aos valores teóricos esperados e apresentam que a difusividade térmica não é alterada radialmente do centro para a extremidade da amostra. Nas amostras nitrocementadas, de geometria circular, circular com furo ao centro, triangular e quadrangular observou-se, pela microscopia óptica e pela determinação da difusividade térmica, que a nitrocimentação não é uniforme ao longo da superfície da amostra e varia conforme sua região, sendo a intensidade maior nas bordas do que no centro. Desta forma, a OPC é uma técnica sensível às mudanças estruturais na superfície de um material, podendo assim ser utilizada para distinguir superfícies que sofreram ou não nitrocementação. Palavras chave: difusividade térmica, fotoacústica, OPC, aço AISI 316

Made available in DSpace on 2017-07-21T19:26:03Z (GMT). No. of bitstreams: 1 Aloisi Somer.pdf: 2418672 bytes, checksum: 5335beb3286a39fbb6b9808f3a874283 (MD5) Previous issue date: 2012-03-09 / The techniques they use photothermal effect, particularty the photoacoustic phenomenon, has been widely used for characterization of materials. The photoacoustic phenomenon arrises when a periodically modulate light falls on a material that absorbs radiation and produces such a variation of pressure in the gas layer adjacent to it. One technique that uses this phenomenon is the technique open photoacoustic cell (OPC), which allows obtaining the thermal diffusivity of a material, defined as= k/. The main mechanism of generation of the photoacosutic signal in solids samples is the thermal diffusion, and its mathematical model proposed by Rosencwaig and Gersho (RG model). But it is observed that the photoacoustic signal, the OPC technique, greatly influenced the thermoelastic bending mechanism which had its model proposed by Rousset et al. To characterize the photoacoustic cell, used for measurements of OPC, aluminum is used. It is used to have a high thermal diffusivity characterizing the process of thermal diffusion which has a simpler model for interpretation. In this paper we mean to obtain the thermal diffusivity of aluminum. For this we use a set of samples of aluminum cut from a same billet. In a sample, after the OPC measurements, there was a heat treatment at 300C for 48 hours to remove possible defects caused by mechanical treatments of cutting and polishing. Through model simulations of RG, we note that the dependence of the photoacoustic signal must always increase with increase frequency. This effect is not observed experimentally. The OPC measurements before and after heat treatment did not show significant differences, confirming that the treatments did not change the mechanical properties of the samples. Samples of aluminum decrease its inclination in a certain frequency range and increased again at high frequencies suggesting an influence of thermoleastic bending of the sample. The results obtained for thermal diffusivity after adjusting the experimental curves with the equation describing the photacoustic signal with contributions from diffusion and thermoelastic bending were satisfactory. Obtained values between 7,6 10 m² /and 8,8 10 m² / , and that the thermal diffusivity calculated from the definition 8,6 10 m² / s . The dependence on the thickness of the sample to a constant weight that provides the thermoelastic bending can be calculated, we find 2,82 s l and the expected value of being3 s l . So we see that the thermoelastic bending is present in the generation of the photoacoustic signal, can not be used simplifications of the RG model for the thermal diffusivity. / As técnicas que utilizam efeito fototérmico, em especial o fenômeno fotoacústico, vem sendo muito utilizadas para a caracterização de materiais. O fenômeno fotoacústico surge quando uma luz periodicamente modulada incide sobre um material, este absorve tal radiação e produz uma variação de pressão na camada de gás adjacente a ele. Uma das técnicas que se utiliza desse fenômeno é a técnica fotoacústica de célula aberta (OPC), que permite a obtenção da difusividade térmica de um material, definida como. O principal mecanismo de geração do sinal fotoacústico em amostras sólidas é a difusão térmica, tendo seu modelo matemático proposto por Rosencwaig e Gersho (modelo R-G). Observa-se que o sinal fotoacústico, na técnica OPC, sofre grande influência do mecanismo de flexão termoelástica que teve seu modelo proposto por Rousset e colaboradores. Para a caracterização do microfone utilizado na célula fotoacústica, utilizada para as medidas de OPC, é utilizado o alumínio. Ele é usado por ter uma alta difusividade térmica caracterizando o processo de difusão térmica que possui um modelo mais simples para interpretação. Neste trabalho temos por objetivo obter a difusividade térmica do alumínio. Para isso utilizamos um conjunto de amostras de alumínio cortadas de um mesmo tarugo. Em uma amostra, após a realização de medidas OPC, foi realizado um tratamento térmico de 300º por 48h para retirar possíveis defeitos provocados pelos tratamentos mecânicos de corte e polimento. Através das simulações do modelo R-G, notamos que a dependência do sinal fotoacústico deve sempre aumentar com o aumento da frequência no regime termicamente grosso devido ao termo exponencial. Efeito que não é observado experimentalmente. As medidas de OPC antes e depois do tratamento térmico não apresentaram diferenças consideráveis, confirmando que os tratamentos mecânicos não mudaram as propriedades das amostras. As amostras de alumínio diminuem a sua inclinação em certo intervalo de frequência voltando a aumentar em altas frequências sugerindo influência da flexão termoelástica da amostra. Os resultados obtidos para a difusividade térmica após o ajuste das curvas experimentais com a equação que descreve o sinal fotoacústico com contribuições da difusão e da flexão termoelástica mostraram-se satisfatórios. Obtivemos valores entre 7,6 10 m² / e 8,8 10 m² /, sendo a difusividade térmica calculada a partir da definição 8,6 10 m² / s. A dependência com a espessura da amostra para a constante que fornece o peso da flexão termoelástica pode ser calculada, encontramos, 82 s l sendo o valor esperado de 3 s l . Portando vemos que a flexão termoelástica é presente na geração do sinal fotoacústico, não podendo ser utilizado as simplificações do modelo de R-G para obter a difusividade térmica.

The main objective of this industrially important work was to gain an increasing understanding of the properties of some industrially important materials such as CMSX-4 nickel base super alloy, 90Ti.6Al.4V alloy, 25Cr:6Ni stainless steel, 0.7% carbon steel, AISI 304 stainless steel-alumina composites, mould powder used in continuous casting of steel as well as coke used in blast furnace with special reference to the thermal diffusivities. The measurements were carried out in a wide temperature range covering solid, liquid, glassy and crystalline states. For CMSX-4 alloy, the thermal conductivities were calculated from the experimental thermal diffusivities. Both the diffusivities and conductivities were found to increase with increasing temperature. Microscopic analysis showed the presence of intermetallic phases γ´ such as Ni3Al below 1253 K. In this region, the mean free path of the electrons and phonons is likely to be limited by scattering against lattice defects. Between 1253 K and solidus temperature, these phases dissolved in the alloy adding to the impurities in the matrix, which, in turn, caused a decrease in the thermal diffusivity. This effect was confirmed by annealing the samples at 1573 K. The thermal diffusivities of the annealed samples measured at 1277, 1403 and 1531 K were found to be lower than the thermal diffusivities of non-annealed samples and the values did not show any noticeable change with time. It could be related to the attainment of equilibrium with the completion of the dissolution of γ´ phase during the annealing process. Liquid CMSX-4 does not show any change of thermal diffusivity with temperature. It may be attributed to the decrease of the mean free path being shorter than characteristic distance between two neighbouring atoms. Same tendency could be observed in the case of 90Ti.6Al.4V alloy. Since the thermal diffusivity increases with increasing temperature below 1225 K and shows slight decrease or constancy at higher temperature. For 25Cr:6Ni stainless steel, the thermal diffusivity is nearly constant up to about 700 K. Beyond that, there is an increase with temperature both during heating as well as cooling cycle. On the other hand, the slope of the curve increases above 950 K, which can be due to the increase of bcc phase in the structure. 0.7% carbon steel shows a decrease in the thermal diffusivity at temperature below Curie point, where the structure contains bcc+ fcc phases. Above this point the thermal diffusivity increases, where the structure contains only fcc phase. The experimental thermal conductivity values of these alloys show good agreement with the calculated values using Mills model. Thermal diffusivity measurements as a function of temperature of sintered AISI 304 stainless steel-alumina composites having various composition, viz, 0.001, 0.01, 0.1, 1, 2, 3, 5, 7, 8 and 10 wt% Al2O3 were carried out in the present work. The thermal diffusivity as well as the thermal conductivity were found to increase with temperature for all composite specimens. The thermal diffusivity/conductivity decreases with increasing weight fraction of alumina in the composites. The experimental results are in good agreement with simple rule of mixture, Eucken equation and developed Ohm´s law model at weight fraction of alumina below 5 wt%. Beyond this, the thermal diffusivity/ conductivity exhibits a high discrepancy probably due to the agglomeration of alumina particles during cold pressing and sintering. On the other hand, thermal diffusivities of industrial mould flux having glassy and crystalline states decrease with increasing temperature at lower temperature and are constant at higher temperature except for one glassy sample. The thermal diffusivity is increased with increasing crystallisation degree of mould flux, which is expected from theoretical considerations. Analogously, the thermal diffusivity measurements of mould flux do not show any significant change with temperature in liquid state. It is likely to be due to the silicate network being largely broken down. In the case of coke, the sample taken from deeper level of the pilot blast furnace is found to have larger thermal diffusivity. This can be correlated to the average crystallite size along the structural c-axis, Lc, which is indicative of the higher degree of graphitisation. This was also confirmed by XRD measurements of the different coke samples. The degree of graphitisation was found to increase with increasing temperature. Further, XRD and heat capacity measurements of coke samples taken from different levels in the shaft of the pilot blast furnace show that the graphitisation of coke was instantaneous between 973 and 1473 K. / QC 20100629

In order to meet the need of metallurgical industry in the world, a new MgAlON-BN composite which can be used for example in special refractory nozzles, tubes and break rings for the continuous casting of steel was studied in the present thesis. The aim was to understand the mechanism of synthesis and their physicochemical properties during the application. Thus, the thermodynamic properties, synthesis process, mechanical properties, thermal shock behaviour, thermal diffusivity/conductivity as well as corrosion resistance to molten iron containing oxygen and molten slag of MgAlON and MgAlON-BN composites have been investigated. The Gibbs energy of formation of MgAlON was estimated using the method proposed by Kaufman. The phase stability diagram of Mg-Al-O-N-B was investigated, and consequently the synthesis parameters were determined. MgAlON and MgAlON-BN composites were fabricated by hot-pressing method. The composites obtained this way were characterized by XRD, SEM, TEM and HREM analyses. A Matrix-flushing method was employed in the quantitative XRD analysis for the multi-component samples to understand the mechanism of synthesis. The relationship between mechanical properties and microstructure of the composites was investigated. The experimental results indicated that BN addition has significant influence on the mechanical properties of the composites. These can be explained by the fact that BN has low Young’s modulus, density and non-reactive nature as well as considerable anisotropy of many properties such as thermal expansion, thermal diffusivity/conductivity. Thus, the addition of BN in MgAlON is likely to lead to the presence of microcracks caused by the mismatch of thermal expansion coefficient. The microcracks result in the enhancement of the strength at elevated temperature and thermal shock durability of the composites. Effective thermal conductivities were evaluated from the present experimental results of thermal diffusivities, heat capacity and density. A model suitable for present composites has been derived based on Luo’s model. The predicted lines calculated by the model were in good agreement with experimental results. The reactions between the composites and molten iron as well as the slag were investigated by ‘‘finger’’ experiments and sessile drop experiments. Both experimental results indicated that the BN addition has positive influence on the corrosion resistance. These are attributed to the excellent corrosion resistance of BN to molten iron and slag, such as the higher contact angle between BN substrate and liquid iron and molten slag compared with that obtained for pure MgAlON. / QC 20100929