Les recherches portant sur le développement des composites réfractaires de type SiCf/SiC pour application gainage du combustible des réacteurs de géneration IV ont conduit le CEA à s’intéresser aucomportement thermique de ces matériaux. En particulier, la connaissance des propriétés thermiques représente un des points cles dans la conception des composants. Au regard du concept sandwichdont la complexité de structure et la géométrie cylindrique s'éloigne de celle d'éprouvettes planes classiquement utilisées, les méthodes de mesures usuelles ne conviennent pas.Ce travail de thèse s’intéresse à la caractérisation et à la modélisation du comportement thermiquede ces structures. Une première partie du travail concerne l'identification des paramètres thermiquesglobaux des différentes couches constitutives d'une gaine sandwich . Pour cela, une méthodeash est employée et un banc d’expériences adapte aux géométries tubulaires a pu être développe.L’écriture d'un nouveau modèle d'estimation, fonde sur le couplage des signaux recueillis à la fois enface avant et en face arrière, permet aujourd'hui d’accéder par la mesure a la diffusivité thermiquedes composites tubulaires via la thermographie infrarouge. Dans une seconde partie de la thèse,une démarche matériau virtuel a été mise en place pour décrire le comportement thermique d'unegaine sandwich à partir des propriétés des constituants élémentaires (bres et matrice). Cespropriétés, obtenues avec deux méthodes d'estimation différentes permettant d'exploiter les mesuresde deux expériences distinctes basées sur la thermographie infrarouge, sont utilisées comme donnéespour la modélisation du transfert thermique au sein de ces gaines. Les confrontations réalisées entrecampagnes de mesures et expériences numériques permettent normalement d’appréhender le poids desdifférents facteurs d'influence qui régissent les transferts thermiques. / Researches on the development on SiCf/SiC refractory composites for generation IV nuclear fuel cladding led the CEA to focus on the thermal behavior of these materials. In particular, knowingthe thermal properties is essential for their components design. Regarding the development of the sandwich" concept, whose complexity and geometry differ from the conventionally used at tubes,usual measurement methods are unsuitable.This PhD reports on the characterization and modeling of the thermal behavior of these structures. The first part concerns the identification of the global thermal parameters of the diferent layers of a"sandwich" sheath. To do so, a ash method is used and an experimental bench suitable for tubular geometries was developed. A new estimation method based on the combination of both collectedsignals in front and rear faces allows the identification of the thermal diffusivity of tubular composites using infrared thermography. The second part focuses on a virtual material approach, established todescribe the thermal behavior of a "sandwich" cladding, starting from the properties of the elementary components (bers and matrix). These properties, obtained using two different estimation methods,allows exploiting the measurements of two separate experiments based on infrared thermography.They are then used as data for the heat transfer modeling in these ducts. Confrontations betweenexperimental measurements and numerical results finally allow gaining insight into the in uence ofthe different key parameters governing the heat transfer.

This study focuses on factors that affect the structural integrity of wood-based composites. Wood-based composites exposed to fire may decompose due to the elevated temperatures, resulting in a degradation in performance. Thermal modelling can only predict the structural integrity of construction materials in fire if it is given accurate inputs. Consequently, methods for the characterization of the thermal, physical, and mechanical behaviors of wood and wood-based composites are selected, designed, and benchmarked. The relevant thermal and physical responses characterized includes porosity, permeability and thermal diffusivity. Common construction materials (white pine board, medium density fiberboard and spruce 24) are characterized from room temperature to complete decomposition. The characterization techniques and processes are based on existing literature and relevant ASTM standards. To reduce the number of experiments required for future material characterization, estimates based upon the degree of decomposition and the measured values for the virgin and charred materials are used. For porosity and thermal diffusivity, these models allow values at intermediate temperatures to be estimated with measurements at room temperature and complete decomposition and thermogravimetric analysis (TGA). We find that permeability depends heavily on the microstructure of materials and should be measured independently at the conditions of interest. An additional important aspect of the performance of wood-based composites is the fracture behavior of wood/adhesive systems. Adhesive bonding enables many engineered wood products such as furniture and structural wood joints and the adhesive fracture toughness often determines the durability. The conventional characterization method for wood/adhesive fracture resistance relies on samples with machined grain angles designed to funnel cracks to the adhesive interface. This method of sample preparation is difficult and time-consuming for certain wood species. In this work, a practical and efficient method is developed to characterize adhesive fracture energy of adhesively bonded veneer systems. In the method, auxiliary aluminum adherends are bonded to the veneers in an effort to drive the crack to the wood/adhesive interface. The method is applied to rotary-peeled veneers and saw-cut veneers produced from three species of wood bonded with three commonly used adhesives. The new tests method yields a high interfacial failure rate and successfully identifies differences in the performance of the three adhesives. SPG (one species of the rotary-peeled veneers) demonstrates a rising R-curve behavior (an increase in the fracture toughness with crack length) when bonded on the loose side. This increase in fracture toughness is observed to be a result of adhesive-substrate interaction, which is a developing process zone behind the crack tip consisting of bridged wood ligaments. / Doctor of Philosophy / Construction materials exposed to elevated temperatures from fires may reach temperatures where the material decomposes from the original material to a char. Protected and unprotected structural timber products exposed to fires may exhibit this behavior resulting in a degradation of performance. Understanding the thermal and physical responses of these materials is crucial in evaluating the materials behavior in fire. Additionally, many wood-based products (such as furniture) rely on adhesive bonds. Consequently, their usefulness is determined by the performance of those bonds. In this work, methods are developed to measure key properties impacting the behavior of wood-based systems at elevated temperatures, such as that experienced in fires and when they are subjected to forces attempting to debond one wood material from another. These techniques are demonstrated on common building materials (white pine board, medium density fiberboard and spruce 24) and wood veneers from three different species bonded with three different adhesives. Mathematical models are developed to expand the use of the data beyond the specific conditions for which it is measured.

Thesis (Ph.D.)--Harvard-Massachusetts Institute of Technology Division of Health Sciences and Technology Program in Medical Engineering and Medical Physics, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE / Vita. / Includes bibliographical references. / by Jonathan Walker Valvano. / Ph.D.

Orientadores: Edson Correa da Silva e Antonio Manoel Mansanares / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin. / Made available in DSpace on 2018-09-26T17:40:21Z (GMT). No. of bitstreams: 1 Albuquerque_MarcosLazarodeSouza_D.pdf: 2664850 bytes, checksum: 47305c651cc9350b772372c3f4181f3e (MD5) Previous issue date: 2008 / Resumo: Neste trabalho desenvolveu-se um experimento de detecção fototémica com dois sensores piroelétricos em uma célula capacitiva que permite a realização de medidas térmicas e elétricas em materiais pastosos em função da temperatura.A célula idealizada para medidas elétricas e térmicas é um capacitor plano de placas paralelas capaz de obter das amostras investigadas os parâmetros de efusividade térmica, difusividade térmica,condutividade térmica e constante dielétrica relativa,simultaneamente,além de detectar transições,em especial fusão.A célula capacitiva fotopiroelétrica é composta por dois sensores piroelétricos entre os quais a amostra é posicionada.Um elemento Peltier associado a um termistor é utilizado para o controle de temperatura.Incide sobre a célula um feixe de radiação eletromagnética oriunda de uma fonte Laser Ar + (514,5 nm ).A radiação modulada atinge diretamente um dos sensores que é opaco e que está em contato térmico com a amostra.O calor gerado no primeiro sensor se propaga, então,pelo sistema amostra-segundo sensor gerando sinais nos dois sensores que são amplificados em amplitude e fase por dois amplificadores seletivos.Ao mesmo tempo,os sinais elétricos da célula capacitiva são registrados por uma ponte RCL operando em 2 kHz.A aquisição de dados dos sinais térmicos é procedida em programa escrito em ambiente LabView para varredura de freqüência de 0 a 100 Hz.Preliminarmente,medidas foram realizadas com margarina e mostraram o potencial da metodologia na verificação do comportamento térmico e elétrico de materiais pastosos.Foi investigado um conjunto de oito amostras constituídas por pares de componentes em proporções e métodos de sínteses diferentes de três tipos de óleos vegetais:algodão,palma e soja.Para a obtenção da constante dielétrica relativa da amostra,o valor da capacitância da mesma foi normalizado pelo valor de capacitância da célula vazia (dielétrico o ar).Modelos para a interpretação dos dados experimentais das medidas térmicas e elétricas foram desenvolvidos.Os gráficos dos sinais de amplitude e fase térmicas detectados pelos sensores foram plotados em função da freqüência de modulação e ajustados pelas equações teóricas dos sensores para a obtenção dos parâmetros térmicos.Foram obtidos valores dos parâmetros efusividade térmica, difusividade térmica,condutividade térmica e constante dielétrica relativa das oito amostras investigadas, além da identificação da região do ponto de fusão das mesmas.Os resultados mostraram que a célula desenvolvida neste trabalho para a aplicação em materiais pastosos pode identificar a região do ponto de fusão,obter os parâmetros térmicos e a constante dielétrica relativa das amostras investigadas / Abstract: This work consists in the development of an experimental apparatus of photopyroelectric detection using two pyroelectric sensors in a capacitive cell which allows the accomplishment of electrical and thermal measurements of pasty materials as a function of the temperature.The idealized cell for electrical and thermal measurements is based in a parallel plane-plate capacitor whose metallic plates are the internal surfaces of the pyroelectric sensors.The system is capable to obtain thermal parameters like effusivity, diffusivity and conductivity,and electric parameters like the dielectric constant for the investigated samples.The identification of the melt point region from either the thermal measurements of the photopyroelectric signal amplitude and phase or the electrical measurements is possible as well.The capacitive photopyroelectric cell is composed by two pyroelectric sensors.An insulator support is used to accommodate the samples which are placed between the sensors.An aluminum piece hold all parts of the cell;one Peltier element is associated with a termistor to control the temperature.An eletromagnetic radiation beam from a Ar + laser incides on the cell and is modulated by an acoustic-optic modulator.The modulated radiation reaches one of the sensors which is opaque and in contact with the sample.Two L ck-in amplifiers amplify the signals originated in each sensor due to the propagation of heat while the electrical signals are registered by an automatic RCL bridge operating at 2 kHz.For data acquisition a Labview language computer software was used allowing to frequency scanning from 0 to 100 Hz. Preliminary experiments were carried out with margarine and showed the methodology pontential in the verification of the thermal and electrical behavior of pasty materials.It was investigated a set of eight samples formed by different compositions of three vegetable oils:cotton,palm and soy in different proportions and within two synthesis methods (basic mixture of intersterification).The sample capacitance was normalized by the empty cell to obtain the relative dielectric constant of the sample.The models for the thermal and electrical data interpretation were developed.For the thermal case simulations were proceeded for a basic oil in order to verify the model.The graphs for thermal amplitude and phase from both sensors were plotted as a function of modulation frequency from which the thermal properties were obtained by fitting the model equations.The values of thermal effusivity,thermal diffusivity, thermal conductivity and relative dielectric constant were obtained for the samples and the transition melting region as well.The results have shown that the cell here developed is very suitable for the determination of thermal and electrical properties of pasty samples and the determination of transition as well. / Doutorado / Física Geral / Doutor em Ciências

Orientador: Jorge Roberto Pimentel / Banca: Roberto Naves Domingos / Banca: Osvaldo Missiato / Resumo: A questão da disposição final dos resíduos sólidos, gerados pelas indústrias e pela população, é um grande desafio a ser solucionado pelas empresas e entidades ligadas à conservação do meio ambiente. Uma das alternativas para o descarte racional destes resíduos é a sua incorporação ao solo. O conhecimento das propriedades térmicas de um solo incorporado com resíduo é importante para garantir que esta alternativa não interfira, por exemplo, na capacidade do solo em difundir energia necessária para o crescimento das plantas. Este trabalho envolveu a determinação da difusividade térmica de amostras de um solo incorporado com resíduo gerado por uma Estação de Tratamento de Água, da cidade de Rio Claro. A determinação da difusividade térmica das amostras foi baseada no método utilizado por CLIVATI (1991). A partir da medição da temperatura em função do tempo, numa determinada posição, foi possível obter as difusividades térmicas de cada amostra em duas condições de umidades diferentes. Para as umidades utilizadas, os resultados mostraram que a incorporação do resíduo de E.T.A nas proporções especificadas não alterou, significativamente, os valores da difusividade térmica do solo estudado. Estes resultados indicam que o fluxo de calor no solo praticamente não é afetado pela incorporação do resíduo. / Abstract: The question of the final disposition of the solid residues generated by the industry and the population is a big challenge to be solved by the corporations and entity concerned with the preservation of the environment. One of the alternatives for the rational dump of these residues is its incorporation to the soil. The knowledge of the thermal properties of a soil incorporated with residue is important to assure that this alternative, for example, doesn't interfere in the capacity of the soil to diffuse the necessary energy for the growth of the plants. This work has involved the determination of the thermal diffusivity in the samples of a soil incorporated with residue generated by a Treatment Water Station (T.W.S.), in the city of Rio Claro. The determination of the thermal diffusivity of the samples was based in the method used by CLIVATI (1991). From the temperature measurement in time function, in the certain position, it was possible to obtain the thermal diffusivities of each sample in two conditions of different moisture. For the used moisture, the results showed that the incorporation of the T.W.S. residue, at the specified proportions, did not change, the thermal diffusivities values of the studied soil in a significant manner. These results indicate that the heat flux in the soil practically is not affected by the residue incorporation. / Mestre

Submitted by Jorge Silva (jorgelmsilva@ufrrj.br) on 2018-08-24T19:38:47Z No. of bitstreams: 1 2016 - Daniela Augusto Chaves.pdf: 7459629 bytes, checksum: db78e044349231645bd60b6c5fb4c66e (MD5) / Made available in DSpace on 2018-08-24T19:38:47Z (GMT). No. of bitstreams: 1 2016 - Daniela Augusto Chaves.pdf: 7459629 bytes, checksum: db78e044349231645bd60b6c5fb4c66e (MD5) Previous issue date: 2016-02-25 / CAPES / The monitoring of soil thermal regime in periglacial environment is critical to identify the presence of permafrost and the thickness of the active layer. This study was conducted to identify factors that influence the soil thermal regime in Keller Peninsula, from 02/2011 to 02/2015. For such monitoring were installed air temperature sensors (Tar) and soil (Ts) and soil moisture at different depths and sites in Keller Peninsula. Preliminary analyzes of the data were based on the monthly average, annual; maximum and minimum averages and seasonal averages of Tar; Ts and soil moisture at different depths in the monitoring sites Ipanema Ref?gio II, Punta and site soil with Standard. After these analyzes identified the days of freezing, thawing, isothermal and freezing / thawing for each depth; the frequency distribution of temperature and temperature fluctuation during the period studied. The analyzes were carried out: the cross-correlation between the AAO series (Antarctic Oscillation Index), SOI (Southern Oscillation Index), Tar and Ts; linar simple regression between the annual average temperatures and the highest average maximum and annual minimum; Multiple linear regression between moisture apparent soil thermal difuvividade (DTA); N_fator the rate of freezing and its relationship with DTA and; the harmonic analysis of the AAO series, SOI, MEI (multivariate ENSO index), Tar and Ts. The highest and lowest Tar annual average in the four years and four sites studied was 1.7 ?C on site Ref?gio II and 4.8 ?C in place with Standard Solo, respectively. The period in which the soil has more time under the active layer system was Ipanema and Ref?gio II. The highest and the lowest sum of degree days of thawing and freezing were 154.6 and 263.3, respectively Ref?gio II In cross-correlation analysis the delay phase between the waves of Tar and Ts was less than one month in all sites. The correlation between the AAO x Tar Tar and SOI x occurs up to 5 months delay between the phases. Simple linear regression analysis indicated that in Ipanema and Ref?gio II, the soil thermal regime restricted the active layer. On site soil with Standard and Punta Plaza thermal regime presented reached the permafrost before the layer of 0.80 and 1.00 m deep respectively. In the frequency histograms showed predominance of temperatures around 0 ?C and the first difference graph shown that temperature variations are stronger in summer. Multiple linear regrass?o analysis showed that the moisture influence on the DTA in most cases. The freezing N_fator was inversely proportional to close DTA the surface, but when compared with the DTA in depth the relationship approaches. The harmonic analysis identified that climate variability in ways that influenced the Tar these sites between the years 2011-2014, were the AAO and SOI indices. In general, the thermal insulation provided by covering the thickest snow in places Punta Plaza and Solo with Standard allowed the permafrost were found at depths less when compared to the Ref?gio II and Ipanema sites that were less thick blanket of snow. / O monitoramento do regime t?rmico do solo em ambiente periglacial ? fundamental para identificar a presen?a do permafrost e a espessura da camada ativa. Este estudo foi realizado para identificar os fatores que influenciam no regime t?rmico do solo na Pen?nsula Keller, entre 02/2011 a 02/2015. Para tal monitoramento foram instalados sensores de temperatura do ar (Tar) e do solo (Ts) e umidade do solo em diferentes profundidades e s?tios na Pen?nsula de Keller. As an?lises preliminares dos dados foram realizadas com base nas m?dias mensais, anuais; m?dias m?ximas e m?nimas e m?dias sazonais de Tar, Ts e umidade do solo em diferentes profundidades nos s?tios de monitoramento Ipanema, Ref?gio II, Punta e s?tio Solo com Padr?o. Ap?s essas an?lises foram identificados os dias de congelamento, descongelamento, isot?rmicos e congelamento/descongelamento para cada profundidade; as frequ?ncias de distribui??o das temperaturas e oscila??o de temperatura durante o per?odo estudado. As an?lises realizadas foram: a de correla??o cruzada entre as s?ries de AAO (Antarctic Oscillation Index), SOI (Southern Oscillation Index), Tar e Ts; a regress?o linar simples entre as temperaturas m?dias anuais e a maior m?dia m?xima e m?nima anuais; a regress?o linear m?ltipla entre umidade a difuvividade t?rmica aparente do solo (DTA); o ?ndice N_fator de congelamento e sua rela??o com a DTA e; a an?lise harm?nica das s?ries AAO, SOI, MEI (multivariate ENSO index), Tar e Ts. A maior e a menor Tar m?dia anual nos quatro anos e nos quatro s?tios estudados foi de -1,7 ?C no s?tio Ref?gio II e de ?4,8 ?C no s?tio Solo com Padr?o, respectivamente. O per?odo em que o solo apresentou mais tempo sob o regime de camada ativa foi Ipanema e Ref?gio II. A maior e a menor soma de graus dias de descongelamento e congelamento foram de 154,6 e ?263,3, respectivamente em Ref?gio II. Na an?lise de correla??o cruzada o atraso de fases entre as ondas de Tar e Ts foi inferior a um m?s em todos os s?tios. A correla??o entre a AAO x Tar e SOI x Tar ocorre com at? cinco meses de atraso entre as fases. A an?lise de regress?o linear simples indicou que, em Ipanema e em Ref?gio II, o regime t?rmico do solo se restringe a camada ativa. No s?tio Solo com Padr?o e Punta Plaza o regime t?rmico apresentado alcan?ou o permafrost antes da camada de 0,80 e 1,00 m de profundidade respectivamente. Os histogramas de frequ?ncia apresentaram predomin?ncia de temperaturas em torno de 0 ?C e o gr?fico de primeira diferen?a mostrou que as varia??es da temperatura foram mais fortes no ver?o. A an?lise de regrass?o linear m?ltipla mostrou que a umidade influencia na DTA na maior parte dos casos. O N_fator de congelamento foi inversamente proporcional a DTA pr?xima a superf?cie, por?m quando o compara com a DTA em profundidade essa rela??o se aproxima. A an?lise harm?nica permitiu identificar que os modos de variabilidade clim?tica que influenciaram a Tar nesses s?tios, entre os anos de 2011 a 2014, foram os ?ndices AAO e SOI. De maneira geral, o isolamento t?rmico proporcionado por cobertura da neve mais espessa nos s?tios Punta Plaza e Solo com Padr?o, permitiu que o permafrost fosse encontrado a profundidades menores quando comparado com os s?tios Ref?gio II e Ipanema, que obtiveram cobertura da neve menos espessa.

Avec la miniaturisation croissante des systèmes micro et nanoélectroniques, les problématiques thermiques revêtent un enjeu croissant. En effet, la faible taille des composants rend problématique l'évacuation de chaleur. Selon la NASA, 90% des défaillances sont imputables à des défauts d'interconnections thermiques et d'après l'US Air Force, 55% des défaillances électroniques sont attribuables à des effets thermiques. Devenues très courantes dans les domaines des nanotechnologies et des énergies renouvelables, les couches minces présentent des caractéristiques thermiques propres (confinement) et des défis métrologiques particuliers (taille des échantillons, influence du substrat sur la mesure). Le transfert de chaleur à l'échelle submicrométrique diffère du transfert de chaleur dans les matériaux massifs à cause de l'effet de confinement spatial propre aux nanostructures. Ainsi, la diffusivité thermique α et la conductivité thermique κ de ces couches minces sont des paramètres qui affectent la performance et la durée de vie de ces couches dans une application donnée. Ce mémoire de thèse porte sur le développement d'un banc de mesure, basé sur les variations de réflectivité d'un matériau en fonction de la température ou thermoréflectance, pour la caractérisation thermique à l'échelle submicrométrique. Dans ce travail, nous avons développé des modèles thermiques tridimensionnels dans des systèmes à deux et trois couches ainsi que les expressions théoriques du signal de thermoréflectance mesuré suite à une excitation thermique de la surface de l'échantillon. Ces expressions ont été développées en tenant compte de l'effet des résistances thermiques aux interfaces. Les modèles ont été validés expérimentalement par des mesures sur des couches minces d'or déposées sur un substrat de silice. Les mesures de thermoréflectance ont été ensuite appliquées à des couches minces d'acide polylactique. Finalement, des couches minces d'oxyde de zinc dopées par différentes concentrations d'aluminium ont été élaborées par voie électrochimique et leurs propriétés thermiques étudiées à l'aide du banc de mesure de thermoréflectance. / With the increasing miniaturization of micro and nanoelectronic systems, the thermal behavior of these systems has become more and more important. The small size of the components makes the heat emitted more troublesome. According to NASA, 90% of failures are due to thermal interconnection faults and according to the US Air Force, 55% of electronic failures are attribuable to thermal effects. Most electronic chips are manufactured using thin films technologies ; therefore, the characteristics of thin metal films have been the bottom line in the ongoing research in nanotechnology and renewable energy domain. Nanoscale heat transfer is different from the heat transfer in bulk materials due to the spatial confinement effect specific to nanostructures. Furthermore, the thermal diffusivity α and thermal conductivity κ of these films are critical parameters affecting their performance and lifetime in a given application. This thesis is devoted to setting up a measurement bench, based on the reflectivity variations of a material as a function of temperature (thermoreflectance), in order to thermally characterize thin films. In this work, a three-dimensional theoretical model is developed in order to describe the temperature distribution in two and three layers systems and obtain the expression of the measured thermoreflectance signal when the surface of the sample is heated by an intensity-modulated Gaussian laser beam. These expressions are obtained by taking into consideration the effect of thermal boundary resistances. These models have been validated experimentally on thin films of gold deposited on fused silica substrate. The thermoreflectance measurements have been then performed on thin films of polylactic acid. Finally, thin films of zinc oxide doped with different concentrations of aluminum have been elaborated during this thesis. The thermal characterization of these films is carried out with the thermoreflectance bench.

<p>The aim of this study is to synthesize a material with high thermal conductivity and a low coefficient of thermal expansion (CTE), useful as a heat sink. Carbon nanofibres (CNF) are first coated with copper by an electroless plating technique and then sintered to a solid sample by either spark plasma sintering (SPS) or hot pressing (HP). The final product is a carbon nanofibre reinforced copper composite. Two different fibre structures are considered: platlet (PL) and herringbone (HB). The influence of the amount of CNF reinforcement (6-24 %wt), on the thermal conductivity and CTE is studied. CNF has an excellent thermal conductivity in the direction along the fibre while it is poor in the transverse direction. The CTE is close to zero in the temperature range of interest. The adhesion of Cu to the CNF surface is in general poor and thus improving the the wetting of the copper by surface modifications of the fibres are of interest such that thermal gaps in the microstructure can be avoided. The poor wetting results in CNF agglomerates, resulting in an inhomogeneous microstructure. In this report a combination of three different types of surface modifications has been tested: (1) electroless deposition of copper was used to improve Cu impregnation of CNF; (2) heat treatment of CNF to improve wetting; and (3) introduction of a Cr buffer layer to further enhance wetting. The obtained composite microstructures are characterized in terms of chemical composition, grain size and degree of agglomeration. In addition their densities are also reported. The thermal properties were evaluated in terms of thermal diffusivity, thermal conductivity and CTE. Cr/Cu coated platelet fibres (6wt% of CNF reinforcement) sintered by SPS is the sample with the highest thermal conductivity, ~200 W/Km. The thermal conductivity is found to decrease with increasing content of CNFs.</p>

To offer better solutions for the recycling of salt cake from secondary aluminum melting, several innovative investigations were carried out based on hydrometallurgical and pyrometallurgical views. Thermal diffusivity measurements as a function of temperature on salts-Al composites having various compositions (0, 2, 4, 6, 8, 10, 12wt pct metallic Al) were carried out. Its attempt to derive theoretical relationships between aluminium contents in the salt-Al composites and the thermal conductivities so that these would serve as calibration curves for industrial samples taken out from secondary aluminium re-melting at a later stage. The AlN hydrolysis behavior in NaCl solution was investigated by immersing pure AlN powder in deionized water, 0.3mol/l NaCl aq, 0.6mol/l NaCl aq and NaCl solution respectively with CO2 bubbling at 291K. The results showed that AlN powder underwent enhanced hydrolysis in NaCl aq than that in deionized water, while, the introduction of CO2 was found to hinder the hydrolysis even in the presence of NaCl. The characterization of the products after hydrolysis was carried out using XRD, SEM and TEM analyses. It was shown that the hydrolysis process included a slow-reaction period involving the dissolution of aluminum hydroxide layer around raw AlN particle, followed by the precipitation of aluminum hydroxide gel and the crystallization of boehmite, bayerite and gibbsite. The effects of sodium chloride concentration on the hydrolysis behavior are presented. The leaching process in CO2-saturated water showed that, at a solid to liquid ratio of 1:20 and 3h at 291K, the extraction of Na and K from the dross could be kept as high as 95.6% and 95.9%, respectively. At the same time, with continuous CO2 bubbling, the mass of generated NH3 during the leaching process decreased significantly, also the escaping NH3 gas decreased from 0.25mg in pure water down to &lt;0.006mg. The above results showed that the introduction of CO2 causes hindrance to the hydrolysis of AlN, meanwhile, effective absorption of ammonia. The plausible mechanisms for the observed phenomena are discussed. The concept of the leaching of the salt cake by carbonated water and the consequent retention of AlN in the leach residue opens up a promising route towards an environment-friendly recycling process for the salt cake viz. recovery of the salts, utilization of CO2 and further processing of the dross residue, towards the synthesis of SiAlON from the leach residues.   In alternative route to the processing of salt cake, the ammonia gas evolved by hydrolysis of AlN was collected by CO2-saturated water during water leaching at 373K. The products, i.e. ammonium carbonates which are free of chlorides, has application as a fertilizer, besides that, this method also has the advantage of fixing carbon from CO2, which is the subject of many investigations around the world. The oxidation behavior of composites SiMgAlON phases (β-SiAlON, MgAlON and 15R) synthesized from the residue during the leaching treatment of salt cake and corresponding synthetic samples was investigated in air by thermogravimetric measurements. The oxidation studies reveal the effects of impurities, namely, Fe2O3 and CaO present in the salt cake residue. From the view of kinetics, the addition of Fe2O3 brings a lower activation energy and more aggressive oxidation. The additive of CaO caused the shrinkage during the synthesis and liquid formation during the oxidation above 1673K, thus retard the oxidation rate. The impurities of CaO and Fe2O3 in the leaching residue can result in an aggressive oxidation at low temperature and a protective oxidation at temperatures above the eutectic point. From the view of phase evolution, with the progress of oxidation, the composition of the material being oxidized moved towards the Al2O3-rich corner of MgO-Al2O3-SiO2 or CaO-MgO-Al2O3-SiO2 phase diagrams relevant to SiMgAlON composite. At lower temperatures, the addition of Fe2O3 and CaO facilitated the formation of cordierite and anorthite, respectively. With the increasing of temperature, islands of silicate melt were formed dissolving these oxides, with the liquidus temperature getting lowered as a consequence. The liquid phase formed engulfed the adjacent solid phases providing strong mobility for the cations and enabling the crystal growth. As a result, intermediate products, i.e. cordierite, anorthite, spinel, which formed earlier during oxidation are found to get dissolved in the liquid phase. / <p>QC 20120912</p>

The aim of this study is to synthesize a material with high thermal conductivity and a low coefficient of thermal expansion (CTE), useful as a heat sink. Carbon nanofibres (CNF) are first coated with copper by an electroless plating technique and then sintered to a solid sample by either spark plasma sintering (SPS) or hot pressing (HP). The final product is a carbon nanofibre reinforced copper composite. Two different fibre structures are considered: platlet (PL) and herringbone (HB). The influence of the amount of CNF reinforcement (6-24 %wt), on the thermal conductivity and CTE is studied. CNF has an excellent thermal conductivity in the direction along the fibre while it is poor in the transverse direction. The CTE is close to zero in the temperature range of interest. The adhesion of Cu to the CNF surface is in general poor and thus improving the the wetting of the copper by surface modifications of the fibres are of interest such that thermal gaps in the microstructure can be avoided. The poor wetting results in CNF agglomerates, resulting in an inhomogeneous microstructure. In this report a combination of three different types of surface modifications has been tested: (1) electroless deposition of copper was used to improve Cu impregnation of CNF; (2) heat treatment of CNF to improve wetting; and (3) introduction of a Cr buffer layer to further enhance wetting. The obtained composite microstructures are characterized in terms of chemical composition, grain size and degree of agglomeration. In addition their densities are also reported. The thermal properties were evaluated in terms of thermal diffusivity, thermal conductivity and CTE. Cr/Cu coated platelet fibres (6wt% of CNF reinforcement) sintered by SPS is the sample with the highest thermal conductivity, ~200 W/Km. The thermal conductivity is found to decrease with increasing content of CNFs.