A espectroscopia fotoacústica (PA) vem sendo largamente utilizada em diversos ramos de pesquisa, principalmente nas investigações de materiais quanto às suas propriedades ópticas e térmicas, demonstrando a sua vasta versatilidade. No presente trabalho, desenvolveu-se uma câmara fotoacústica de uso geral e uma metodologia baseada na técnica fotoacústica, técnica não intrusiva e não destrutiva, para a determinação da porosidade aberta de membranas vítreas. A porosidade aberta de membranas vítreas está relacionada diretamente à permeabilidade e à eficiência dessas membranas em processos de filtração. Essas membranas foram processadas utilizando-se a técnica de preenchimento e garrafas de vidro, encontradas comercialmente, como matéria-prima. Através da utilização de NaCl como o material inerte, foram processadas membranas com diferentes percentagens de poros. A metodologia fotoacústica desenvolvida neste trabalho teve como base modelos teóricos fotoacústicos tradicionais de análise. Esta metodologia foi capaz de determinar a porosidade aberta das membranas e de distinguí-las quanto as suas superfícies. Os resultados obtidos através da técnica fotoacústica foram comparados com os resultados obtidos por porosimetria de mercúrio (técnica intrusiva e destrutiva) e por ensaios de permeabilidade (técnica intrusiva e não destrutiva) com as mesmas membranas. Estas duas técnicas de análise são as usualmente utilizadas em estudos de estruturas porosas. A comparação entre os dados experimentais comprovou a validade dos resultados obtidos com a nova metodologia. Além desta metodologia fornecer a porosidade aberta com relativa facilidade, ela demonstrou ser rápida, não-destrutiva e de baixo custo para cada ensaio nas análises / The photoacoustic (PA) spectroscopy has been used in several research lines, mainly in the investigation of thermal and optical properties related to different materials, showing in this way high versatility. In this work is described the development of a general-purpose photoacoustic cell, and of a methodology based on photoacoustic technique for the determination of the opened porosity of vitreous membranes. The technique is non-intrusive and non-destructive in relation to the membranes. The opened porosity of vitreous membranes is directly related to the permeability and also directly related to the efficiency of these membranes in the filtration processes. Membranes with different percentage of pores were processed by means of filler principle. For this purpose were used glass bottles found commercially as raw material and NaCl as inert material. The photoacoustic methodology developed in this work was based on classical theoretical models found in the literature. This methodology was capable to determine the open porosity of the membranes and to distinguish membranes with different surfaces. The results obtained with the photoacoustic technique were compared with that obtained by means of mercury porosimetry (intrusive and destructive technique) and permeability measurements (intrusive and non destructive technique) with the same membranes. These two techniques are usually used in studies of porous structures. The comparison between the experimental data showed the validity of the results obtained with this new methodology. Moreover, it supplies the opened porosity with relative easiness, in a faster and non-destructive way, and with low cost in the analyses

A espectroscopia fotoacústica (PA) vem sendo largamente utilizada em diversos ramos de pesquisa, principalmente nas investigações de materiais quanto às suas propriedades ópticas e térmicas, demonstrando a sua vasta versatilidade. No presente trabalho, desenvolveu-se uma câmara fotoacústica de uso geral e uma metodologia baseada na técnica fotoacústica, técnica não intrusiva e não destrutiva, para a determinação da porosidade aberta de membranas vítreas. A porosidade aberta de membranas vítreas está relacionada diretamente à permeabilidade e à eficiência dessas membranas em processos de filtração. Essas membranas foram processadas utilizando-se a técnica de preenchimento e garrafas de vidro, encontradas comercialmente, como matéria-prima. Através da utilização de NaCl como o material inerte, foram processadas membranas com diferentes percentagens de poros. A metodologia fotoacústica desenvolvida neste trabalho teve como base modelos teóricos fotoacústicos tradicionais de análise. Esta metodologia foi capaz de determinar a porosidade aberta das membranas e de distinguí-las quanto as suas superfícies. Os resultados obtidos através da técnica fotoacústica foram comparados com os resultados obtidos por porosimetria de mercúrio (técnica intrusiva e destrutiva) e por ensaios de permeabilidade (técnica intrusiva e não destrutiva) com as mesmas membranas. Estas duas técnicas de análise são as usualmente utilizadas em estudos de estruturas porosas. A comparação entre os dados experimentais comprovou a validade dos resultados obtidos com a nova metodologia. Além desta metodologia fornecer a porosidade aberta com relativa facilidade, ela demonstrou ser rápida, não-destrutiva e de baixo custo para cada ensaio nas análises / The photoacoustic (PA) spectroscopy has been used in several research lines, mainly in the investigation of thermal and optical properties related to different materials, showing in this way high versatility. In this work is described the development of a general-purpose photoacoustic cell, and of a methodology based on photoacoustic technique for the determination of the opened porosity of vitreous membranes. The technique is non-intrusive and non-destructive in relation to the membranes. The opened porosity of vitreous membranes is directly related to the permeability and also directly related to the efficiency of these membranes in the filtration processes. Membranes with different percentage of pores were processed by means of filler principle. For this purpose were used glass bottles found commercially as raw material and NaCl as inert material. The photoacoustic methodology developed in this work was based on classical theoretical models found in the literature. This methodology was capable to determine the open porosity of the membranes and to distinguish membranes with different surfaces. The results obtained with the photoacoustic technique were compared with that obtained by means of mercury porosimetry (intrusive and destructive technique) and permeability measurements (intrusive and non destructive technique) with the same membranes. These two techniques are usually used in studies of porous structures. The comparison between the experimental data showed the validity of the results obtained with this new methodology. Moreover, it supplies the opened porosity with relative easiness, in a faster and non-destructive way, and with low cost in the analyses

Lisovanie za tepla (HIP) je pokročilá technológia pre výrobu plne hutných keramických materiálov, ktoré majú množstvo štruktúrnych (napr. rezné nástroje), biologických (napr. implantáty hutných kostí a kĺbov) alebo funkčných (napr. transparentné štíty a okná) aplikácií. Pre úspešné použitie tejto technológie je potrebné, aby predspekané vzorky boli plynotesné, teda bez otvorených pórov. Výskum zaoberajúci sa premenou otvorených pórov na uzatvorené je preto veľmi dôležitý, avšak iba málo publikovaný v odbornej literatúre. Preto bolo experimentálne a teoretické štúdium tohto javu hlavným cieľom diplomovej práce. Analýzy teoretických modelov ukazujú, že transformácia z otvorenej na uzatvorenú pórovitosť je materiálová charakteristika, ktoré sa mení iba s dihedrálnym uhlom, nezávisle na veľkosti častíc prášku alebo na spôsobe tvarovania a nastáva od 92.6% t.d. do 93.7% t.d pre daný materiál (oxid hlinitý, oxid zirkoničitý a horečnato-hlinitý spinel). Tieto teoretické výpočty boli porovnané s experimentálnymi dátami z literatúry a dátami z experimentálnej časti diplomovej práce s úspešnou zhodou pre kubické systémy (spinel a kubický oxid zirkoničitý). Výsledky experimentov s oxidom hlinitým boli v dobrej zhode s experimentálnymi dátami publikovanými v literatúre, ale boli vyššie ako teoretické hodnoty. Na objasnenie týchto odlišností bolo vytvorených niekoľko hypotéz a tiež boli navrhnuté spôsoby riešenia tejto témy.

The thesis targets to preparation a foam ceramics suitable for supporting, catalytic and biological applications. Theoretical part deals with methods of preparation, properties and applications of foam ceramics. Experimental part of work is focused on preparation foams by template method using polymer foam. Properties of ceramic slurry were evaluated according to discharge time of Ford cup. Foam structure is assessed using images and mechanical properties are judged by compressive tests.

Baigiamajame magistro darbe analizuojami cementinio akmens poringumo parametrai. Darbe siekiama palyginti cementinio akmens bandinių su skirtingais vandens ir cemento santykiais poringumo parametrus, gautus pagal skirtingas poringumo parametrų tyrimo metodikas. Apžvelgta literatūra lietuvių, anglų ir rusų kalbomis. Išanalizuotas cementinio akmens ilgalaikiškumo ir poringumo ryšys, įvairių parametrų įtaka cementinio akmens poringumui bei orą įtraukiančių priedų įtaka poringumui reguliuoti. Aprašytos cementinio akmens gamybai naudotos medžiagos: portlandcementis, vanduo ir superplastiklis. Darbe projektuojami trys skirtingi cementinio akmens mišiniai, kurie skiriasi vandens ir cemento santykiu. Pateiktos cementinio akmens mišinių sudėtys. Aprašytos tyrimų metodikos, pagal kurias nustatyti cementinio akmens poringumo parametrai. Atlikti sukietėjusio cementinio akmens tyrimai bei jų palyginimas. Tyrimų duomenys apdoroti kompiuterinėmis programomis „Microsoft Excel“ ir „UTHSCSA ImageTool“, išanalizuoti gauti rezultatai bei pateiktos išvados. Darbą sudaro 5 dalys: įvadas, literatūros analizė, medžiagos ir tyrimai, išvados, literatūros sąrašas. Darbo apimtis – 74 p. teksto, 30 iliustr., 20 lent., 40 bibliografiniai šaltiniai. / The master thesis analyzes hardened cement paste porosity parameters. The aim of work is to campare methods for determination of porosity parameters of hardened cement paste samples with different w/c ratios. Reviewed the literature in Lithuanian, English and Russian languages. Was analyzed the bond beatween durability and porosity, influence of various parameters to hardened cement pastes porosity and influence of air-entraining admixtures to control porosity. Was analyzed the concrete making materials: cement, water and superplasticizer. The work is designed three different cement stone mixtures with different w/c ratios. Presented cement stone compositions of mixtures and set their properties. Described research methodology, by which established hardened cement paste porosity parameters. With solidified cement stone made researches. The research data treated by computer programs Microsoft Excel and UTHSCSA ImageTool, done an analysis of the results and made conclusions. Structure: introduction, literature review, materials and research, conclusions, references. Thesis consist of: 74 p. text without appendixes, 30 pictures, 20 tables, 40 bibliographical entries.

Une option à l'étude pour le recyclage des actinides mineurs consiste à en incorporer environ 10% à une matrice d'UO2. La présence de pores ouverts interconnectés au sein de ce combustible devrait permettre d'évacuer l'hélium et les gaz de fission pour prévenir le gonflement de la pastille et in fine son interaction avec la gaine qui l'entoure. La mise en oeuvre des actinides mineurs oblige à travailler en cellule blindée, à minimiser leur rétention et à proscrire les ajouts de produits organiques. L'emploi de particules fragmentables de quelques centaines de micromètres paraît une solution intéressante pour contrôler la microstructure des comprimés crus et ainsi maîtriser la porosité ouverte après frittage. L'étude consiste à suivre par émission acoustique la compaction de particules fragiles d'UO2 et à relier leurs caractéristiques à la porosité ouverte obtenue après frittage des compacts. Le signal acquis lors d'essais de cisaillement sur des granulés individuels et sur des compacts montre que l'émission acoustique autorise la détection de la fragmentation et permet l'identification d'une forme d'onde caractéristique. Les influences de la contrainte de compaction, de la distribution granulométrique initiale et de la cohésion interne des granulés, sur la tenue mécanique des compacts et sur la microstructure des frittés, en particulier sur la porosité ouverte sont analysées. Moyennant quelques précautions, l'émission acoustique, par sa capacité à déterminer le domaine de fragmentation des granulés pendant la mise en forme, paraît une technique prometteuse pour suivre la compaction de particules fragiles en vue de la fabrication de combustibles à porosité maîtrisée. / One of the options considered for recycling minor actinides is to incorporate about 10% to UO2 matrix. The presence of open pores interconnected within this fuel should allow the evacuation of helium and fission gases to prevent swelling of the pellet and ultimately its interaction with the fuel clad surrounding it.Implementation of minor actinides requires working in shielded cell, reducing their retention and outlawing additions of organic products. The use of fragmentable particles of several hundred micrometers seems a good solution to control the microstructure of the green compacts and thus control the open porosity after sintering.The goal of this study is to monitor the compaction of brittle UO2 particles by acoustic emission and to link the particle characteristics to the open porosity obtained after the compact sintering.The signals acquired during tensile strength tests on individual granules and compacts show that the acoustic emission allows the detection of the mechanism of fragmentation and enables identification of a characteristic waveform of this fragmentation.The influences of compaction stress, of the initial particle size distribution and of the internal cohesion of the granules, on the mechanical strength of the compact and on the microstructure and open porosity of the sintered pellets, are analyzed.By its ability to identify the range of fragmentation of the granules during compaction, acoustic emission appears as a promising technique for monitoring the compaction of brittle particles in the manufacture of a controlled porosity fuel.

En centrales nucléaires, un accident grave est une séquence très peu probable d’événements durant laquelle des composants du réacteur sont significativement endommagés, par interactions chimiques et/ou fusion, à cause de très hautes températures. Cela peut mener à des rejets radiotoxiques dans l’enceinte et à une entrée d’air dans le réacteur. Dans ce contexte, ce travail de thèse mené chez EDF R&D visait à modéliser la détérioration du gainage combustible, en alliages de zirconium, en conditions accidentelles : haute température et soit vapeur soit mélange air-vapeur. L’objectif final était d’améliorer la simulation par le code MAAP de l’oxydation du gainage et de la production d’hydrogène, en particulier pendant un renoyage avec de l’eau. Dû à l’épaississement progressif d’une couche de ZrO2 dense et protectrice, la cinétique d’oxydation du Zr en vapeur à hautes températures est généralement (sous-)parabolique. Cependant, à certaines températures, cette couche d’oxyde peut se fissurer, devenant poreuse et non protectrice. Par ce processus de « breakaway », la cinétique d’oxydation devient plus linéaire. De plus, l’augmentation de température peut mener les matériaux du réacteur à fondre et à se relocaliser dans le fond de cuve dont la rupture peut induire une entrée d’air dans le réacteur. Dans ce cas, l’oxygène et l’azote réagissent avec les gaines pré-oxydées, successivement par oxydation du Zr (épaississant la couche de ZrO2), nitruration du Zr (formant des particules de ZrN) et oxydation du ZrN (créant de l’oxyde et relâchant de l’azote). Ces réactions auto-entretenues relancent la fissuration du gainage et de sa couche de ZrO2, induisant une hausse de sa porosité ouverte. Afin de quantifier cette porosité du gainage, un protocole expérimental innovant en deux étapes a été défini et appliqué : il consistait à soumettre des échantillons de gainage en ZIRLO® à diverses conditions accidentelles pendant plusieurs durées puis à des mesures de la porosité ouverte par porosimétrie par intrusion de mercure. Les conditions de corrosion comprenaient plusieurs températures allant de 1100 à 1500 K ainsi que de la vapeur et un mélange air-vapeur 50-50 mol%. Pour les échantillons de ZIRLO® oxydés en vapeur, sauf à 1200 et 1250 K, les transitions de cinétique n’ont pas lieu et la porosité ouverte reste négligeable au cours de l’oxydation. Cependant, pour les autres échantillons, corrodés en air-vapeur ou oxydés en vapeur à 1200 ou 1250 K, des transitions « breakaway » sont observées et les résultats de porosimétrie montrent que la porosité ouverte augmente au cours de la corrosion, proportionnellement au gain en masse. De plus, il a été mis en évidence que la distribution de tailles de pores des échantillons de ZIRLO® s’étend significativement pendant la corrosion, en particulier après « breakaway ». En effet, ces tailles vont de 60 μm à environ : 2 μm avant la transition, 50 nm juste après et 2 nm plus longtemps après. Enfin, un modèle numérique en deux étapes a été développé dans le code MAAP pour améliorer sa simulation de l’oxydation du gainage. D’abord, grâce à la proportionnalité entre porosité ouverte et gain en masse des échantillons, des corrélations de porosité ont été implémentées pour chaque condition de corrosion. Ensuite, les valeurs de porosité calculées sont utilisées pour augmenter proportionnellement la vitesse d’oxydation du gainage. Ce modèle amélioré simule ainsi non seulement les réactions chimiques des gaines en Zr (oxydation et nitruration) mais aussi leur dégradation mécanique et son impact sur leur vitesse d’oxydation. Ceci a été validé en simulant des essais QUENCH (-06, -08, -10 et -16), conduits au KIT pour étudier le comportement de gaines dans des conditions accidentelles avec un renoyage final. Ces simulations montrent un meilleur comportement thermique du gainage et une production d’hydrogène significativement plus haute et donc plus proche des valeurs expérimentales, en particulier pendant le renoyage. / In nuclear power plants, a severe accident is a very unlikely sequence of events during which components of the reactor core get significantly damaged, through chemical interactions and/or melting, because of very high temperatures. This may potentially lead to radiotoxic releases in the containment building and to air ingress in the reactor core. In that context, this thesis work led at EDF R&D aimed at modeling the deterioration of the nuclear fuel cladding, made of zirconium alloys, in accidental conditions: high temperature and either pure steam or air-steam mixture. The final objective was to improve the simulation by the MAAP code of the cladding oxidation and of the hydrogen production, in particular during a core reflooding with water. Due to the progressive thickening of a dense and protective ZrO2 layer, the oxidation kinetics of Zr in steam at high temperatures is generally (sub-)parabolic. However, at certain temperatures, this oxide layer may crack, becoming porous and not protective anymore. By this “breakaway” process, the oxidation kinetics becomes rather linear. Additionally, the temperature increase can lead core materials to melt and to relocate down to the vessel lower head whose failure may induce air ingress into the reactor core. In this event, oxygen and nitrogen both react with the pre-oxidized claddings, successively through oxidation of Zr (thickening the ZrO2 layer), nitriding of Zr (forming ZrN particles) and oxidation of ZrN (creating oxide and releasing nitrogen). These self-sustained reactions enhance the cracking of the cladding and of its ZrO2 layer, inducing a rise of its open porosity.In order to quantify this cladding porosity, an innovative two-step experimental protocol was defined and applied: it consisted in submitting ZIRLO® cladding samples first to various accidental conditions during several time periods and then to measurements of the open porosity through porosimetry by mercury intrusion. The tested corrosion conditions included numerous temperatures ranging from 1100 up to 1500 K as well as both pure steam and a 50-50 mol% air-steam mixture. For the ZIRLO® samples oxidized in pure steam, except at 1200 and 1250 K, the “breakaway” kinetic transitions do not occur and the open porosity remains negligible along the oxidation process. However, for all other samples, corroded in air-steam or oxidized in pure steam at 1200 or 1250 K, “breakaway” transitions are observed and the porosimetry results show that the open porosity increases along the corrosion process, proportionally to the mass gain. Moreover, it was evidenced that the pore size distribution of ZIRLO® samples significantly extends during corrosion, especially after “breakaway” transitions. Indeed, the detected pore sizes ranged from 60 μm down to around: 2 μm before the transition, 50 nm just after and 2 nm longer after. Finally, a two-step numerical model was developed in the MAAP code to improve its simulation of the cladding oxidation. First, thanks to the proportionality between open porosity and mass gain of cladding samples, porosity correlations were implemented for each tested corrosion condition. Second, the calculated porosity values are used to proportionally enhance the cladding oxidation rate. This improved model thus simulates not only chemical reactions of Zr-based claddings (oxidation and nitriding) but also their mechanical degradation and its impact on their oxidation rate. It was validated by simulating QUENCH tests (-06, -08, -10 and -16), conducted at KIT to study the behavior of claddings in accidental conditions with a final reflooding. These simulations show a better cladding thermal behavior and a hydrogen production significantly higher and so closer to experimental values, in particular during the reflooding.