Orientador: Antonio Manoel Mansanares. / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin. / Made available in DSpace on 2018-08-12T12:29:07Z (GMT). No. of bitstreams: 1 Guimaraes_AndreOliveira_D.pdf: 2906238 bytes, checksum: a8ad8b4fc0c3d5bbca6671977306a943 (MD5) Previous issue date: 2008 / Resumo: Neste trabalho foram desenvolvidas montagens experimentais baseadas na detecção foto acústica para o estudo de materiais magnetocalóricos, que têm despertado um grande interesse na comunidade científica em virtude de suas possíveis aplicações em sistemas de refrigeração. Utilizando o método de dois feixes, para a configuração fotoacústica ar-amostra-ar, foi possível determinar para a difusividade térmica do Gd, em temperatura ambiente, o valor de (4,5 ± 0,2).10-6 m2/s, por meio da amplitude e da fase do sinal fotoacústico normalizado. Medidas da fase do sinal em varreduras de temperatura permitiram a determinação da difusividade térmica em torno da transição magnética (TC), de forma confiáavel e reprodutiva,a com erros menores que 5%. Com base em princípios envolvidos na fotoacústica, foi desenvolvido um método para medidas do efeito magnetocalórico (EMC). O aquecimento gerado nos materiais em questão pela aplicação de um campo magnético alternado (AC), via efeito magnetocalórico, dá origem a ondas de pressão num gás, que são detectadas por um microfone. Discutiu-se sobre os procedimentos de calibracão envolvidos e a metodologia utilizada para a determinação do efeito. Foram realizadas medidas com amostras de Gd e compostos da família Gd5(Ge1-xSix)4, em pó e em pastilhas. Para um campo aplicado de 20 kOe, os valores máximos do EMC vão de 3 K, para o Gd, a 4,5 K, para os compostos ricos em Si, e se referem a transições magnéticas de segunda ordem. Para amostras com x = 0,5, os valores máximos do EMC estão em torno de 1,7 K, referentes a transições magneto-estruturais de primeira ordem. Para alguns destes compostos e possível observar os dois tipos de transição. Os resultados indicam que a técnica se mostra eficiente, não só para as medidas do efeito em si, mas também para a identificação de fases indesejadas, decorrentes do processo de preparação das amostras. Os erros nas medidas do EMC estão em torno de 15 - 20%, comparáveis aos dos métodos convencionais / Abstract: In this work the photoacoustic technique was used to develop experimental setups to investigate magnetocaloric materials, which have been of great interest due to their applications in refrigeration systems. The value (4,5 ± 0,2).10-6 m2/s was determined, at room temperature, as the thermal di usivity of the Gd, based on the two-beam photoacoustic method, by means of both amplitude and phase of the normalized signal. The thermal diffusivity at temperatures around the magnetic transition (TC) was obtained from the photoacoustic signal phase, in temperature scans, in a reproductible and accurate way, with errors below 5%. A method for measuring the magnetocaloric e ect (MCE), based on the acoustic detection, was developed. The temperature oscillations on such materials, due to the application of an alternating magnetic field, produce acoustic waves which can be detected by a microphone. The details concerning the calibration procedure and the proposed methodology to determine the MCE were discussed, and measurements on Gd and Gd 5(Ge1-xSix)4 compouds were performed in powder and pellet samples. For a 20 kOe applied field, the maximum MCE values, related to magnetic second order transitions, are between 3 K, for the Gd, and 4,5 K, for Si - rich compounds. For the samples with x = 0,5, the maximum MCE values are around 1,7 K, related to magneto-structural first order transitions. It is also possible, for some samples, to observe both first and second order transitions. The obtained results point out this acoustic type detection as an effcient technique to measure the magnetocaloric effect, as well as to detect spurious phases present in some of these compounds. The errors in the MCE measurements are about 15-20%, compared to conventional methods / Doutorado / Física da Matéria Condensada / Doutor em Ciências

Thermal diffusivity in an important thermophysical property that quantifies the ratio of the rate at which heat is conducted through a material to the amount of energy stored in a material. The pulsed laser diffusion (PLD) method is a widely used technique for measuring thermal diffusivities of materials. This technique is based on the fact that the diffusivity of a sample may be inferred from measurement of the time-dependent temperature profile at a point on the surface of a sample that has been exposed to a pulse of radiant energy from a laser or flash lamp. An accepted standard approach for the PLD method is based on a simple model of a PLD measurement system. However, the standard approach is based on idealizations that are difficult to achieve in practice. Therefore, models that treat a PLD measurement system with greater fidelity are desired. The objective of this research is to develop and test a higher fidelity model that more accurately represents the spatial and temporal variations in the input power. This higher fidelity model is referred to as Distributed Source Finite Absorption (DSFA) model. The cost of the increased fidelity associated with the DSFA model is an increase in the complexity of inferring values of the thermal diffusivity. A new method of extracting values from time dependent temperature measurements based on a genetic algorithm and on reduced order modeling was developed. The primary contribution of this thesis is a detailed discussion of the development and numerical verification of this proposed new method for measuring the thermal diffusivity of various materials. Verification of the proposed new method was conducted using numerical experiments. A detailed model of a PLD system was created using advanced engineering software, and detailed simulations, including conjugate heat transfer and solution of the full Navier-Stokes equations, were used to generate multiple numerical data sets. These numerical data sets were then used to infer the thermal diffusivity and other properties of the sample using the proposed new method. These numerical data sets were also used as inputs to the standard approach. The results of this verification study show that the proposed new method is able to infer the thermal diffusivity of samples to within 4.93%, the absorption coefficient to within 10.57 % and the heat capacity of the samples to within 5.37 %. Application of the standard approach to these same data sets gave much poorer estimates of the thermal diffusivity, particularly when the absorption coefficient of the material was relatively low.

In the near future, Gen II, III, and IV nuclear reactors will be in operation. UO2 is a common fuel for reactors in each of these generations and molten salts are used as coolant/fuel in Gen IV molten salt reactors. This thesis investigates potential ways to measure thermal conductivity for these materials: Raman thermometry for UO2 and a needle probe for molten salts. Four Raman thermometry techniques are investigated in this thesis: The Two Laser Raman (TLR), Time Differential Domain Raman (TDDR), Frequency Resolved Raman (FRR), and Frequency Domain Raman (FDR). The TLR is a steady state method used with a thin film. The TDDR and FRR are both time domain methods used with thin cantilever samples. The FDR is a frequency domain method used with a thermally thick sample. Monte Carlo like simulations are performed for each technique. In the simulations, the affect introduced uncertainty has on the measurement of thermal conductivity and thermal diffusivity is measured. From the results, it is recommended that the TLR should be used for measuring thermal conductivity and the FRR used for measuring thermal diffusivity. The TDDR and FDR were heavily affected by the uncertainty which resulted in inconsistent measured thermal properties. For measuring the thermal conductivity of molten salt, a needle probe was designed and manufactured to withstand the corrosive environment found in using molten salts. The probe uses modulated joule heating and measures the temperature rise in a thermocouple. The phase delay and temperature amplitude of the thermocouple are used in determining the thermal conductivity. A new thermal quadrupole based analytical solution, which takes into consideration convection and radiation, to the temperature rise of the probe is presented. The analytical solution is verified using a numerical solution found using COMSOL. Preliminary data was obtained with the probe in water.

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No description available.

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