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1
Овчаренко, О. О., М. Д. Сахненко i М. В. Ведь. "Електрохімічний синтез дисперсно-зміцнених композитів Ni-Al[2]O[3]". Thesis, Сумський державний університет, 2016. http://essuir.sumdu.edu.ua/handle/123456789/45670.
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Призначення електрохімічних металевих покриттів полягає, головним чином, в захисті поверхні деталей і виробів від корозії, а також, надання їм декоративного виду. Композиційні електрохімічні покриття (КЕП) використовують для підвищення твердості, зносостійкості, жаростійкості деталей машин, механізмів, поліпшення їх антифрикційних властивостей, підвищення коефіцієнта віддзеркалення і поліпшення ряду інших характеристик.
2
LEAL, NETO RICARDO M. "Sintese por combustao do NbAl-3 e de ligas do sistema Nb-Ni-Al". reponame:Repositório Institucional do IPEN, 1998. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10661.
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Made available in DSpace on 2014-10-09T12:42:49Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:08:07Z (GMT). No. of bitstreams: 0
Tese(Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Javel, Jean-François. "Suivi par diffraction X en temps réel de la formation par combustion auto-entretenue d'intermétalliques : cas de composés appartenant aux systèmes Al-Ni, Al-Ti et Al-Ni-Ti". Nancy 1, 1997. http://www.theses.fr/1997NAN10207.
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A l'aide d'un faisceau X intense fourni par le synchrotron DCI du LURE (Orsay) associé à un détecteur rapide de photons X, la synthèse par combustion auto-entretenue de composés intermétalliques appartenant aux systèmes AI-Ni, AI-Ti et AI-Ni-Ti a pu être suivie en temps réel. Généralement, pour chacune des expériences réalisées, une succession ininterrompue de 2048 diffractogrammes de 30 ms chacun est enregistrée. Le nombre important d'expériences réussies (environ 2/3) montre que le système de déclenchement des réactions (réalisé par notre équipe) et celui d'acquisition des diffractogrammes sont fiables. Grâce à des informations complémentaires, obtenues par l'observation à la microsonde d'échantillons dont la combustion a été brutalement stoppée, un mécanisme de réaction est proposé pour chacun des composés étudiés. Enfin, la présence d'un thermocouple à l'intérieur de chacun des échantillons et d'une caméra infrarouge a permis d'avoir une idée approximative de l'évolution de la température au cours de la combustion.
4
Spätig, Philippe. "Rôle de l'activation thermique dans la plasticité de composés intermétalliques ordonnés: Ni₃(Al,X) /". Lausanne, 1995. http://library.epfl.ch/theses/?nr=1407.
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Souza, Marcos Vinicios de. "Estudo da reorientação de spin nos compostos RX2 (R = terra rara; X: Al, Ni)". Pós-Graduação em Física, 2013. https://ri.ufs.br/handle/riufs/5290.
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In this work, our initial efforts have been directed to study the behavior of the magnetization as a function of temperature, calculated according to the approximate method of the anisotropy constants and the resolution of a Hamiltonian (that includes the crystal field) as exemplified for the DyAl2 compound. Furthermore, we investigated the magneto-thermal characteristics of some members of the RX2 series (R: rare earth, X: Al, Ni), including spin reorientation (SR), by using a model Hamiltonian, that consists of localized magnetic moments interacting via exchange and crystal field interaction, in the molecular-field approximation. We studied how the SR depends on the direction of the application of magnetic field, the intensity of this field and temperature. For the magnetic calculations, the problem of self-consistency was solved by using a computational routine developed in the Fortran 90 programming language. We emphasize that special attention was directed to the crystal field, because of its high relevance to the anisotropic characteristics of the RX2 studied compounds. Thus, in our attempts to study the peculiarities of the rare earth elements, due to crystal field effects, we have not only considered the intensity change, but the direction change of the applied field. In the cases of both Er+3 and Tb+3 compounds, we obtained second-order or continuous magnetization behavior along the polar angle axis. We stressed that the crystal field terms plays an important role in the first order spin reorientation for Dy+3 and Ho+3 compounds. First, it can be revealed by the discontinuity in the Cartesian components of the magnetization vector as a function of the polar angle. Second, the discontinuity is of great importance in the calculation of latent heat associated to the spin reorientation in the case where the first order transitions were observed. Finally, we were able to separate the first and second order contributions of the anisotropic magnetic entropy change, which is the main result of this work.Neste trabalho, nossos esforços iniciais foram direcionados a estudar o comportamento da magnetização em função da temperatura, calculado segundo o método aproximativo das constantes de anisotropia e da resolução de um hamiltoniano (que inclui o campo cristalino) como exemplificado para o composto DyAl2. Além disto, investigamos as características magneto-térmicas de alguns integrantes da série RX2 (R: Terra rara; X: Al, Ni), incluindo a reorientação de spin (RS), usando um hamiltoniano modelo que consiste de momentos magnéticos localizados interagentes via interações de troca e de campo cristalino, na aproximação do campo molecular. Estudamos como a RS depende da direção de aplicação do campo magnético, da sua intensidade e da temperatura. Para os cálculos magnéticos, o problema da auto consistência foi solucionado utilizando uma rotina, computacional desenvolvida na linguagem computacional Fortran 90. Ressaltamos que, uma atenção especial foi direcionada ao campo cristalino, por conta da sua alta relevância sobre as características anisotrópicas dos compostos RX2 estudados. Portanto, em nossas tentativas para estudar as peculiaridades dos elementos terras raras, devido aos efeitos do campo cristalino, não consideramos somente a mudança na intensidade, mas a variação na direção do campo aplicado. No caso dos compostos Er+3 e Tb+3, obteve-se um comportamento da magnetização de segunda ordem ou contínuo face à mudança do ângulo polar. Salientamos que os termos de campo cristalino desempenham um papel fundamental na reorientação de spin de primeira ordem para Dy+3 e Ho+3. Primeiro, tal transição pode ser revelada por uma descontinuidade nas componentes cartesianas do vetor de magnetização em função do ângulo polar. Segundo, a descontinuidade é de grande importância para o cálculo do calor latente associado à reorientação spin nos casos em que foram observadas as transições de primeira ordem. Finalmente, foi possível separar as contribuições de primeira e segunda ordem da variação de entropia magnética anisotrópica, o qual é o principal resultado deste trabalho.
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Krzelowski, Mirosław. "Analiza struktury faz Laves'a Nb (Cu, Al, X) 2 (X = Ni, Co, Cr, Ti i Zr) metodą krystalografii elektronowej". Doctoral thesis, Katowice : Uniwersytet Śląski, 2008. http://hdl.handle.net/20.500.12128/5130.
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Aktualnie prowadzone badania w różnych ośrodkach naukowych związane z poszukiwaniem coraz to bardziej wytrzymałych i odpornych na degradację termiczną materiałów wskazują jednoznacznie, że jednym z właściwych kierunków badań jest zainteresowanie się materiałami, których struktura zawiera fazy międzymetaliczne. Fazami takimi są ponad wszelką wątpliwość fazy Laves’a, które stwarzają dodatkowe możliwości znacznej poprawy różnych charakterystyk tych materiałów, nie powodując jednocześnie
pogorszenia innych pożądanych właściwości. Przykładem są tu stopy typu Cu-Al-Nb wykazujące pamięć kształtu w podwyższonych temperaturach. Obecność w tych stopach wydzieleń fazy Laves’a typu Nb(Cu,Al)2 powoduje równoczesny wzrost właściwości wytrzymałościowych i plastycznych. Wprowadzenie do tych stopów czwartego pierwiastka stopowego prowadzi do dalszych zmian, jednakże nie zawsze korzystnych.
Spowodowane to jest pojawieniem niewielkiej ilości innych faz międzymetalicznych jak również zmianami w składzie chemicznym, strukturze i właściwościach samej fazy Laves’a (Nb(Cu,Al,X)2, gdzie X - czwarty pierwiastek stopowy). Ze względu na rozmiary tych wydzieleń, badanie zmian ich struktury prowadzone jest głównie przy pomocy transmisyjnej mikroskopii elektronowej. Celem pracy jest zbadanie wpływu składu chemicznego na strukturę fazy Laves’a typu Nb(Cu,Al,X)2, gdzie (X = Ni, Co, Cr, Ti lub Zr), wykorzystując głównie metodę krystalografii elektronowej.
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Perricone, Aurélie. "Synthèses, structures cristallines et propriétés magnétiques de nouveaux composés intermétalliques dans le système binaire U-Ni et les systèmes ternaires U-Ni-X (X ; Ge, Si, Al)". Rennes 1, 2002. http://www.theses.fr/2002REN10024.
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Ce mémoire relate les études structurales et les mesures magnétiques effectuées sur les binaires U-Ni et les ternaires des systèmes U-Ni-X (X:Ge,Si,Al). L'étude complète de ces diagrammes de phases a permis de caractériser 6 binaires dans U-Ni:U6Ni(type U6Mn)-UNi2(type MgZn2)-UNi5(type AuBe5)-U10Ni13-U11Ni16 et U1+xNi5-x(type CaCu5),6 ternaires dans U-Ni-Ge:UNi0,45Ge2(type CeNiSi2)-UNi5Ge3(type YNi5Si3)-U3Ni6Ge2(type Ag8Ca3)-U3Ni12-xGe4+y(type Gd3Ru4Al12)-UNi4,2Ge0,8(type CaCu5)-UNi1-xGe1+x;9 dans U-Ni-Si:UNi2,2Si3,3(type Ca2Cu6P5)-U2Ni2Si6,3(type V5B6)-U3Ni11,7Si4(type Gd3Ru4+yAl12-x)-UNi4,5Si0,5(type CaCu5)-U2Ni10,30Si2,64(type Th2Zn17)-U2Ni14,7Si7,3-UNi6,6Si5,7-U2Ni15,9Si6,4 et UNi10Si2;et 5 dans U-Ni-Al:U6Ni12Al5-UNi2+xAl3-x(type CaCu5)-UNi4+xAl2-x(type YMo2Al4)-UNi4,55Al0,45(type CaCu5) et U4Ni11Al2. Parmi ces composés, 9 cristallisent dans une structure inédite:U10Ni13-U11Ni16-UNi1-xGe1+x(0,33
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Verelst, Marc. "Elaboration et caracterisation de composites a matrice metallique ni/al#2o#3 et ni/cr#2o#3 par codeposition electrochimique. Application a l'electroformage de spheres creuses". Toulouse 3, 1991. http://www.theses.fr/1991TOU30111.
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Ce travail concerne l'elaboration par electroformage de spheres creuses a hautes caracteristiques thermomecaniques destinees a la realisation d'un nouveau materiau composite obtenu par brasage des spheres suivant une structure ordonnee. Notre choix s'est porte sur la synthese par codeposition electrochimique de materiaux composites a matrice metallique (m. M. C. ) a base de nickel renforce par de l'alumine ou du sesquioxyde de chrome. Dans une premiere partie de nos travaux, nous synthetisons des poudres submicroniques de ces deux oxydes dispersables en solution aqueuse. Nous presentons ensuite une etude systematique de l'influence des parametres electrochimiques sur la codeposition en courant continu. Afin d'accroitre la proportion de particules codeposees nous avons utilise un plan d'experiences simplex applique a la codeposition par courants pulses. La fraction volumique d'alumine codepose a pu etre accrue de 45% par rapport au courant continu. Une autre technique a consiste a doper en surface l'alumine par du sesquioxyde cr#2o#3 et par de l'oxyde de nickel nio. La progression est significative; la fraction volumique codeposee evolue de 2,4 a 3 et 3,4%. Les composites sont ensuite caracterises d'un point de vue microstructural et thermomecanique. Ces materiaux presentent avant et apres traitement thermique des proprietes tres superieures au nickel pur. Nous montrons que le mode de renforcement est imputable a des effets complexes et conjugues de plusieurs processus elementaires
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Giebel, Dawid. "Kompleksowa analiza widm czasów życia pozytonów oraz jej zastosowanie do badania struktury defektowej stopów z układu Fe-Al i Fe-Al-X (gdzie X=Cr, Ni)". Doctoral thesis, Katowice : Uniwersytet Śląski, 2012. http://hdl.handle.net/20.500.12128/5375.
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Cele niniejszej pracy obejmują dwa główne zagadnienia:
Zaprojektowanie i wykonanie nowej wersji programu komputerowego z serii LT (LT 10),
służącego do analizy widm czasów życia pozytonów
oraz zastosowanie tego programu do badania struktury defektowej stopów z układu Fe-
Al i Fe-Al-X (X=Cr, Ni).
Nowa wersja programu powinna charakteryzować się nowoczesną formą, dostosowaną
do współczesnych systemów operacyjnych komputerów oraz uwzględnić, rozwinąć i zebrać w
jedną całość wszystkie sposoby analizy widm, wprowadzone w poprzednich wersjach LT, takie
jak możliwość jednoczesnej analizy wielu widm za pomocą wybranych modeli
teoretycznych czy możliwość korelowania określonych parametrów widm poprzez nakładanie
różnych typów więzów. Chociaż stworzenie nowego programu komputerowego jest autonomicznym
zadaniem, w tym szczególnym przypadku posłużył on do realizacji drugiego celu
pracy, polegającego na uzyskiwaniu oryginalnych wyników dotyczących struktury defektowej
badanych stopów, trudnych czy wręcz niemożliwych do otrzymania przy zastosowaniu dotychczas
istniejącego oprogramowania.
Praca jest podzielona na trzy zasadnicze części: część teoretyczną, obejmującą przegląd literaturowy zagadnień związanych z
badanymi w tej pracy materiałami oraz z omówieniem metod wyznaczania
struktury defektowej materiałów, ze szczególnym uwzględnieniem metod pozytonowych,
część metodologiczną, poświęconą zagadnieniom związanym z analizą widm
czasów życia pozytonów i ich realizacją za pomocą programu LT 10,
część eksperymentalną,dotyczącą opisu badań eksperymentalnych stopów z
układu Fe-Al i Fe-Al-X, wyników tych badań i ich dyskusji .
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Carrier, Xavier. "Phenomenes a l'interface oxyde/solution aqueuse lors de la preparation de catalyseurs supportes : apports de la geochimie application a la preparation de catalyseurs moo x/al 2o 3 et wo x/al 2o 3". Paris 6, 1998. http://www.theses.fr/1998PA066437.
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Ce travail vise a demonter le role de reactif que peut jouer le support oxyde lors de la synthese de catalyseurs heterogenes. Le support est generalement considere comme inerte chimiquement au cours des premieres etapes de preparation d'un catalyseur, et on considere que son role se limite a disperser la phase active. Nous montrons i) qu'il est necessaire de prendre en compte la reactivite du support oxyde et ii) que cette prise en compte beneficie des concepts et methodes etablis en geochimie. Ainsi, nous montrons que l'alumine n'est pas thermodynamiquement stable en solution. Sa mise en suspension conduit a la formation d'un hydroxyde al(oh) 3 par un mecanisme de dissolution/precipitation. La formation de cette phase est inhibee par la presence d'anions (moo 2 4, wo 2 4) en solution. En presence de cations (pt(nh 3) 2 + 4), cette formation depend de la methode de preparation. Cette phase influence le comportement du catalyseur final puisqu'elle controle la quantite d'hydrogene spillover formee pendant la reduction. Dans le cas de la preparation de catalyseurs moo x/al 2o 3 par adsorption a l'equilibre, nous montrons qu'il se forme en solution un heteropolyanion al(oh) 6mo 6o 3 1 8 par simple mise en contact d'une suspension d'alumine et d'une solution d'heptamolybdate et que cette espece est deposee en surface du support. La formation de ce compose mixte augmente thermodynamiquement la solubilite du support. Dans le cas d'une preparation par impregnation a sec, ce compose mixte precipite sous forme d'un sel en surface du support ce qui conduit, apres calcination, a la formation d'oxyde moo 3. La formation de ce sel est evitee en lyophilisant le catalyseur ce qui limite la dissolution du support et inhibe la formation ulterieure d'oxyde. Ces conclusions sont etendues a la preparation de catalyseurs wo x/al 2o 3 ou l'on met en evidence la formation d'aluminotungstates en solution et leur depot en surface du support.
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Khan, Muhammad Yaqoob [Verfasser]. "Probing the antiferromagnetism of NixMn100−x with ferromagnetic Ni in exchange-biased bilayers and trilayers on Cu3Au(001) / Muhammad Yaqoob Khan". Berlin : Freie Universität Berlin, 2012. http://d-nb.info/1027816177/34.
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SCAGLIOTTI, MAURO. "Dynamique de reseau et ordre magnetique dans les composes mpx#3 (m=mn, fe, ni, zn, x=s, se)". Paris 6, 1989. http://www.theses.fr/1989PA066449.
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Les trichalcogenures de phosphore et de metaux de transition sont des composes lamellaires antiferromagnetiques qui peuvent etre employes avec succes comme cathodes dans des piles au lithium. Dans ce travail de these nous avons etudie a l'aide de la spectroscopie raman la dynamique de reseau des phases pures, et les transitions electroniques de basses energies a l'interieur du niveau 3d du fer dans les trichalcogenures de phosphore et de fer. Nous avons entrepris un calcul de dynamique de reseau a l'aide d'un modele de constantes de force a symetrie axiale, qui nous permet de corriger les precedentes attributions des pices raman phononiques et de prevoir les proprietes vibrationnelles des phases intercalees. En dessous de la temperature de neel nous avons observe l'apparition de nouveaux pics phononiques dans le spectre raman du trisulfure de phosphore et de fer. Cet effet est correle a l'ordre antiferromagnetique. En particulier nous avons montre que les nouveaux pics pourraient etre phonons des points m et a de la zone de brillouin actives par le dedoublement de la maille elementaire soit dans le plan ab soit le long de l'axe c. Le changement de symetrie du champ cristallin de trigonale a monoclinique, du a un effet de magnetostriction, est aussi responsable de l'anomale polarisation de la diffusion raman electronique dans le trisulfure de phosphore et de fer
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Masquelier, Christian. "Synthèse, structure cristalline et propriétés de transport de cations de phosphates et arséniates : Na#7M#3(X#2O#7)#4 (M=Al, Ga, Cr, Fr; X=P, As); Na#3M#2(Aso#4)#3 (M=Al, Cr, Fe)". Paris 11, 1991. http://www.theses.fr/1991PA112181.
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Cette etude a pour but de preciser les relations entre la structure cristalline et les proprietes de transport de cations de deux familles de composes a charpente tridimensionnelle: les diphosphates et diarseniates na#7m#3(x#2o#7)#4 (m=al, ga, cr, fe; x=p, as); les arseniates na#3m#2(aso#4)#3 (m=al, cr, fe). Les composes na#7m#3(x#2o#7)#4 ont ete prepares par des methodes de flux. Ils presentent, a des temperatures inferieures a 300c, une transition de type ordre-desordre des ions sodium. L'evolution thermique a haute temperature a ete suivie a l'aide de techniques multiples (atd, atg, diffraction x, analyse chimique). La structure cristalline a la temperature ambiante de alpha-na#7fe#3(p#2o#7)#4 et beta-na#7fe#3(as#2o#7) a ete etablie. La forme alpha, qui est une surstructure de la forme beta, est caracterisee par un ordre a longue distance des ions sodium. Ces composes sont echangeurs des cations et des conducteurs de performances moderees; les mesures sur monocristaux revelent que la conduction est essentiellement bidimensionnelle. La seconde partie de ce travail est consacree a la resolution de la structure de plusieurs arseniates na#3m#2(aso#4)#3. Ils cristallisent sous deux formes qui different considerablement par leurs proprietes de transport de cations. Les caracteristiques structurales des composes na#3m#2(aso#4)#3 (m=cr, fe) de forme grenat sont peu favorables a la mobilite des ions na#+. Na#7fe#4(aso#4)#6 differe du compose stchiometrique na#3fe#2(aso#4)#3 rhomboedrique par l'occupation totale du site na(2) et la presence sur le site fe(1) de fer a l'etat fe#2#+. Na#3al#2(aso#4)#3 presente a la temperature ambiante une distorsion monoclinique (groupe d'espace c2) associee a un ordre a longue distance des ions sodium.
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Coad, S. "Neutron scattering on single crystals of Cuâ†1â†-â†x(Zn/Ni)â†xGeOâ†3 and other exotic low dimensional systems". Thesis, University of Warwick, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245935.
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Pasturel, Mathieu. "Modification par hydruration des propriétés structurales et physiques des intermétalliques CeTX (T = Mn, Ni, Cu ; X = Al, Ga, In, Si, Ge, Sn)". Phd thesis, Université Sciences et Technologies - Bordeaux I, 2004. http://tel.archives-ouvertes.fr/tel-00010063.
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Les propriétés physiques des intermétalliques CeTX (T = élément de transition, X = élément np1 ou np2) dépendent de la force de l'hybridation Jcf entre les électrons 4f du cérium et ceux de la bande de conduction. L'insertion d'hydrogène dans ces composés modifie à la fois le volume molaire et la densité d'états au niveau de Fermi, et donc Jcf. Au cours de ce travail, la modification par hydruration des propriétés structurales, magnétiques et électriques des familles suivantes a été étudiée: (i) CeNiX (X = Al, Ga, In, Si, Ge, Sn) qui présentent un caractère de valence intermédiaire du cérium; (ii) CeCuX (X = Ga, Si, Ge, Sn) qui présentent un état trivalent du cérium et l'apparition d'un ordre magnétique à basse température; (iii) CeMnX (X = Si, Ge) qui présentent un ordre magnétique du cérium et du manganèse. Les résultats sont discutés en faisant le parallèle entre les propriétés structurales (sites d'insertion de l'hydrogène) et les propriétés physiques.
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Saib, Djamila. "Reactions d'arylation d'olefines catalysees par la montmorillonite k10 et la montmorillonite de marnia (algerie) echangee par les cations al**(3+), cr**(3+), zn**(2+), ni**(2+), cu**(2+)". Rennes 1, 1988. http://www.theses.fr/1988REN10001.
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Mellul, Sylvie. "Contribution a l'etude de l'interface cu-al : :(2)o::(3) par microscopie electronique en transmission et micro analyse x". Paris 6, 1988. http://www.theses.fr/1988PA066415.
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Bellamy, Bernard. "Agregats metalliques ni, pd, pt/sio::(2), al::(2)o::(3) : influence de la taille sur la structure electronique et la reactivite". Paris 6, 1987. http://www.theses.fr/1987PA066255.
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Preparation d'un modele de catalyseur par la technique des jets atomiques. Les echantillons ont ete prepares par condensation de la vapeur du metal (ni, pd, pt) sur un substrat plat, soit de silice amorphe, soit d'alumine amorphe. Etude du mecanisme de croissance et de la structure electronique des particules metalliques par rheed, spectrometrie auger et spectrometrie de photoelectrons. Mesure du taux de recouvrement absolu et de la distribution de taille
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DAGHIGH, SHAHBOD. "Evolution des contraintes dans le systeme ni#7#0cr#3#0/cr#2o#3 en fonction de la temperature. Etude in situ par diffraction des rayons x et modelisation". Paris 11, 1996. http://www.theses.fr/1996PA112313.
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La diffraction x en temperature a ete utilisee pour mesurer les coefficients de dilatation de l'alliage ni-30cr et de l'oxyde cr#2o#3 entre 20 et 900c, puis pour determiner les contraintes generees dans la couche de cr#2o#3 formee sur nicr en jouant sur diverses variables: epaisseur de la couche et du substrat, taille des grains, dopage en yttrium et vitesse de refroidissement. Par ailleurs, l'etude experimentale des phenomenes de relaxation a ete suivie par le biais de recuits isothermes ou anisothermes apres oxydation a 900c. Apres oxydation et retour a 25c, les contraintes residuelles sont de compression dans l'oxyde et lors d'un chauffage ulterieur, elles diminuent avec la temperature et le temps croissants et tendent vers une valeur quasi nulle a 900c, indiquant ainsi que les contraintes de croissance sont negligeables. Parallelement, un modele numerique de prevision des contraintes et des phenomenes de relaxation a ete developpe en tenant compte du comportement mecanique du substrat et de la couche et de parametres tels que: la vitesse de refroidissement, le temps de maintien, etc. . . Ce modele elasto-visco-plastique rend bien compte de l'evolution des resultats experimentaux avec les diverses variables de l'etude. Un modele par les elements finis a ete egalement developpe afin d'etudier les gradients de contraintes et leur influence sur les phenomenes de fluage et relaxation
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Quetz, Abdiel. "PHASE TRANSITIONS AND MAGNETOCALORIC EFFECT IN MnNiGe1−xAlx, Ni50Mn35(In1−xCrx)15 AND (Mn1−xCrx)NiGe1.05". OpenSIUC, 2014. https://opensiuc.lib.siu.edu/theses/1514.
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The magnetocaloric and thermomagnetic properties of the MnNiGe1-xAlx, Ni50Mn35(In1−xCrx)15 and (Mn1−xCrx)NiGe1.05 systems have been studied by x-ray diffraction, differential scanning calorimetry (DSC), and magnetization measurements. Partial substitution of Al for Ge in MnNiGe1−xAlx results in a first-order magnetostructural transition (MST) from a hexagonal ferromagnetic to an orthorhombic antiferromagnetic phase at 186 K (for x = 0.09). A large magnetic entropy change of ∆SM = -17.6 J/kg K for ∆H = 5 T was observed in the vicinity of TM = 186 K for x = 0.09. This value is comparable to those of well-known giant magnetocaloric materials, such as Gd5Si2Ge2, MnFeP0.45As0.55, and Ni50Mn37Sn13 [1]. The values of the latent heat (L = 6.6 J/g) and corresponding total entropy changes (∆ST = 35 J/kg K) have been evaluated for the MST using DSC measurements. Large negative values of ∆SM of -5.8 and -4.8 J/kg K for ∆H = 5 T in the vicinity of TC were observed for x = 0.09 and 0.085, respectively. Partial substitution of Cr for Mn in(Mn1−xCrx)NiGe1.05 results in a MST from a hexagonal paramagnetic to an orthorhombic paramagnetic phase near TM ~ 380 K (for x = 0.07). Partial substitution of Cr for In in Ni50Mn35(In1−xCrx)15 shifts the magnetostructural transition to a higher temperature (TM ~ 450 K) for x = 0.1. Large magnetic entropy changes of ∆SM = -12 (J/kgK) and ∆S = -11 (J/kgK), both for a magnetic field change of 5 T, were observed in the vicinity of TM for (Mn1−xCrx)NiGe1.05 and Ni50Mn35(In1−xCrx)15, respectively. The concentration-dependent (T-x) phase diagram of transition temperatures (magnetic, structural, and magnetostructural) has been generated using magnetic, XRD, and DSC data. The role of magnetic and structural changes on transition temperatures are discussed.
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Férey, Marie-Amélie. "Élaboration et caractérisation d'alliages hydrurables de type ABx (A=La, Mg ; B=Ni ET x=3 à 4) en vue de leur utilisation comme matière active pour électrode négative d'accumulateur Ni-MH". Phd thesis, Université Paris-Est, 2008. http://tel.archives-ouvertes.fr/tel-00623152.
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Les applications portables et stationnaires des accumulateurs Ni-MH nécessitent sans cesse des autonomies de plus en plus importantes. Cet accroissement d'autonomie peut être obtenu en développant de nouveaux composés intermétalliques hydrurables de type ABx (3
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Petit, Férey Marie Amélie. "Élaboration et caractérisation d'alliages hydrurables de type ABx (A=La, Mg ; B=Ni ET x=3 à 4) en vue de leur utilisation comme matière active pour électrode négative d'accumulateur Ni-MH". Thesis, Paris Est, 2008. http://www.theses.fr/2008PEST0007/document.
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Les applications portables et stationnaires des accumulateurs Ni-MH nécessitent sans cesse des autonomies de plus en plus importantes. Cet accroissement d’autonomie peut être obtenu en développant de nouveaux composés intermétalliques hydrurables de type ABx (3Mobile and stationary applications for Ni-MH batteries require continuously more and more energy density. This increased autonomy can be obtained by developing new hydride-forming compounds of ABx-type (3
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Petit, Férey Marie Amélie Latroche Michel. "Élaboration et caractérisation d'alliages hydrurables de type ABx (A=La, Mg ; B=Ni ET x=3 à 4) en vue de leur utilisation comme matière active pour électrode négative d'accumulateur Ni-MH". S. l. : S. n, 2008. http://doxa.scd.univ-paris12.fr:80/theses/th0411772.pdf.
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Rettenwander, Daniel, Walter Schmidt, Christian Arrer, Martin Wilkening i Georg Amthauer. "The Site Preference of Al and Ga in Mixed Doped Li7−3(x+y)GaxAlyLa3Zr2O12 Garnet Solid Solutions with x, y ∈ {0.1, 0.2, …, 0.8 ∧ y + x ≤ 0.8} and its Influence on Li-Ion Mobility". Diffusion fundamentals 21 (2014) 14, S.1, 2014. https://ul.qucosa.de/id/qucosa%3A32422.
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Kuntz, Sebastian [Verfasser], i H. v. [Akademischer Betreuer] Löhneysen. "Thermal Expansion and Magnetostriction of the Partially Frustrated Heavy-Fermion Metal CePd$_1-x}$Ni$_x$Al at Low Temperatures / Sebastian Kuntz ; Betreuer: H. v. Löhneysen". Karlsruhe : KIT-Bibliothek, 2019. http://d-nb.info/1184990107/34.
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SILVA, Fabiano Sousa Arruda. "Avaliação do processo de reforma seca do metano em reator de membrana". Universidade Federal de Pernambuco, 2009. https://repositorio.ufpe.br/handle/123456789/6482.
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Previous issue date: 2009Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
O desenvolvimento do processo de reforma do metano com dióxido de carbono abordado na presente pesquisa recorre à ação do catalisador de níquel suportado em alumina, disposto em reator de leito fixo com membrana seletiva para hidrogênio associada. Atividade e estabilidade do sistema de níquel (50mg), foram avaliadas através de contato catalisador com uma mistura gasosa de composição em razões molares de alimentação CH4/CO2/Ar (10%/40%/50%), a uma vazão total fixa de 100 cm3/min, operando-se na faixa de temperatura de 1.023 K e 1.073 K, sob pressão de 1,0 bar. A reação de Boudouard (C+CO2→2CO) foi utilizada como base para a regeneração do catalisador de níquel, sob coqueamento, tendo-se observado retomadas de níveis de conversão do metano e de produção de hidrogênio. Operações em reator de membrana, na linha de desenvolvimento do processo, com 2 g de catalisador de níquel (3,31% em massa suportado em alumina), utilizaram uma mistura de reagentes em razões molares CH4/CO2/Ar (40,50%/14,00%/45,50%), com uma vazão total de 110 cm3/min , aplicando-se as temperaturas de 773 K, 823 K e 873 K, sob pressão de 1,0 bar. O processo de reforma seca do metano com dióxido de carbono foi operado em reator de leito fixo de membrana com permeação de hidrogênio, evidenciando uma importante conversão do metano com um rendimento em hidrogênio elevado. A 873 K, sob 1,0 bar de pressão, converteu-se neste sistema 35% de metano rendendo 47% de hidrogênio, significando aumentos de conversão em cerca de 83 % e de rendimento em hidrogênio de mais de 100%, em relação às operações em leito fixo sem permeação. Modelagem e simulações foram elaboradas a partir da cinética já ajustada, permitindo simulações retratando perfis de concentração dos reagentes (CH4 + CO2) e produtos (H2 + CO) com e sem permeação do hidrogênio através da membrana Pd-Ag, destacando-se os efeitos da temperatura
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Pechev, Stanislav. "Synthèse et caractérisation des propriétés structurales et magnétiques de nouveaux siliciures et germaniures à base d'uranium et de cuivre. Etude des propriétés physiques et d'hydruration de quelques composés appartenant aux systèmes Gd - Ni - X où X = Ga, Al, Sn". Phd thesis, Université Sciences et Technologies - Bordeaux I, 1998. http://tel.archives-ouvertes.fr/tel-00003520.
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L'étude des systèmes ternaires U - Cu - X (X = Si ou Ge) a permis de mettre en évidence trois nouvelles phases: U3Cu4Si4, U3Cu4Ge4 et UCuGe1,77. Leurs propriétés structurales et magnétiques ont été étudiées et les structures magnétiques des deux premières ont été déterminées. La substitution du cuivre au silicium dans la solution solide UCuxSi2-x (0,28 ≤ x ≤ 0,96) est à l'origine de transitions structurales et magnétiques selon les séquence α-ThSi2(quadratique) → AlB2(hexagonal) → Ni2In(hexagonal) et non magnétique → ferromagnétique → antiferromagnétique. L'évolution des propriétés magnétiques reflète la compétition entre les interactions de type Kondo et RKKY. Désordre cristallographique et frustrations magnétiques sont à l'origine d'un état "verre de spin" au passage ferro-antiferromagnétique. Les propriétés structurales et magnétiques des composés GdNi3X2 (X =Ga, Al, Sn) se sont avérées fortement dépendantes de la nature de l'élément X et du traitement thermique des échantillons. L'augmentation de la taille de X favorise une transition structurale de type CaCu5 → HoNi2,6Ga2,4 ainsi qu'un passage ferro → antiferromagnétique. Une structure cristallographique modulée commensurable (équivalente à une surstructure aHoNi2,6Ga2,4 × aHoNi2,6Ga2,4 × 2cHoNi2,6Ga2,4) est observée pour GdNi3Al2. L'insertion d'hydrogène dans Gd3Ni6Al2 et GdNi3Al2 affaiblit considérablement les interactions magnétiques.
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Pechev, Stanislav. "Synthèse et caractérisation des propriétés structurales et magnétiques de nouveaux siliciures et germaniures à base d'uranium et de cuivre : étude des propriétés physiques et d'hydruration de quelques composés appartenant aux systèmes Gd-Ni-X où X=Ga, Al, Sn". Bordeaux 1, 1998. http://www.theses.fr/1998BOR10599.
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L'etude des systemes ternaires u - cu - x (x = si ou ge) a permis de mettre en evidence trois nouvelles phases : u#3cu#4si#4, u#3cu#4ge#4 et ucuge#1#,#7#7. Leurs proprietes structurales et magnetiques ont ete etudiees et les structures magnetiques des deux premieres ont ete determinees. La substitution du cuivre au silicium dans la solution solide ucu#xsi#2##x (0,28 x 0,96) est a l'origine de transitions structurales et magnetiques selon les sequence -thsi#2(quadratique) alb#2(hexagonal) ni#2in(hexagonal) et non magnetique ferromagnetique antiferromagnetique. L'evolution des proprietes magnetiques reflete la competition entre les interactions de type kondo et rkky. Desordre cristallographique et frustrations magnetiques sont a l'origine d'un etat verre de spin au passage ferro-antiferromagnetique. Les proprietes structurales et magnetiques des composes gdni#3x#2 (x = ga, al, sn) se sont averees fortement dependantes de la nature de l'element x et du traitement thermique des echantillons. L'augmentation de la taille de x favorise une transition structurale de type cacu#5 honi#2#,#6ga#2#,#4 ainsi qu'un passage ferro antiferromagnetique. Une structure cristallographique modulee commensurable (equivalente a une surstructure #ahoni#2#,#6ga#2#,#4 #ahoni#2#,#6ga#2#,#4 #2#choni#2#,#6ga#2#,#4) est observee pour gdni#3al#2. L'insertion d'hydrogene dans gd#3ni#6al#2 et gdni#3al#2 affaiblit considerablement les interactions magnetiques.
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Kolli, T. (Tanja). "Pd/Al2O3 -based automotive exhaust gas catalysts:the effect of BaO and OSC material on NOx reduction". Doctoral thesis, University of Oulu, 2006. http://urn.fi/urn:isbn:9514280563.
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Abstract
The aim of the thesis was to find new information on the effect of BaO and oxygen storage capacity material on NOx reduction. A total of nine different kinds of Pd/Al2O3-based metallic monoliths were studied. Promoters such as oxygen storage capacity material (OSC material in our case Cex-1ZrxO2 mixed oxides) and stabilisers such as barium (BaO) were added into the catalyst alone or together to improve catalyst properties such as catalytic activity, selectivity, and thermal stability.
The key aspects in this thesis can be divided into four parts. First, the behaviour of NO reduction and CO as well as C2H4 oxidation over Pd/Al2O3-based catalysts in rich, stoichiometric and lean conditions were studied. Secondly, the effect of BaO and the OSC material in NO reduction was considered. Thirdly, the preparation procedure, i.e. the addition order of BaO, OSC material, and Pd on the catalyst was considered. Finally, the effect of ageing on the behaviour of catalysts was investigated.
Several characterization methods (in situ DRIFT, catalytic activity measurements, N2 physisorption, CO chemisorption, dynamic oxygen storage capacity measurements, and X-ray diffraction (XRD)) were utilised to find answers to the behaviour of these catalysts in the studied model reactions. The Rapid Ageing Hot in Laboratory (RAHLAB) method was used to age the catalyst.
First, it was demonstrated that the CO and hydrocarbon oxidation and NO reduction reactions over the Pd/Al2O3-based catalyst behave differently. NO reduction and CO and hydrocarbon oxidation reactions were dependent on the reaction conditions and temperatures. Secondly, the effect of OSC and BaO on NO reduction was studied separately. In the case of OSC material, it was observed that the OSC material has an effect on NO reduction as well as on CO and C2H4 oxidation. In the case of BaO, it was observed that BaO has a positive effect on NO reduction as well as CO and C2H4 oxidation especially in rich conditions. Thirdly, the effects of the addition order of OSC and BaO on the catalyst was studied separately. It was shown that these have an effect on NO reduction, especially after ageing. First, on the fresh Pd/Al2O3 catalyst it was observed that the addition order of OSC on the catalyst has not an influence on catalyst performance. The effect of the BaO addition order on the Pd/OSC/Al2O3-based catalyst is found to be insignificant, especially, after the ageing process. Furthermore, it is observed that the effect of RAHLAB ageing was that the catalyst lost its catalytic activity, stability, and selectivity.
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Lemort, Lucille. "Élaboration et caractérisation d'alliages hydrurables de type ABx (A=Pr, Nd, La, Mg ; B=Ni; x=3, 3.5, 3.8, 5) en vue de leur utilisation comme matière active pour électrode négative d'accumulateurs NiMH". Phd thesis, Université Paris-Est, 2010. http://tel.archives-ouvertes.fr/tel-00599399.
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Une alternative aux énergies fossiles comme vecteur énergétique peut se présenter sous la forme de l'hydrogène et de son stockage. Les hydrures métalliques sont une des options possibles pour le stockage de l'hydrogène. Les accumulateurs alcalins Ni-MH présentent une technologie intéressante pour les applications portables et pour le développement des véhicules électriques hybrides (HEV). Afin de répondre à la demande d'augmentation de la capacité massique des accumulateurs, de nouveaux composés intermétalliques hydrurables de type ABx (3etlt;xetlt;5) sont étudiés. Le groupe A est constitué de terres rares partiellement substituées par du magnésium, le groupe B contient du Ni. Après un état de l'art sur ce type de composés, le travail de cette thèse consiste à rechercher les conditions d'élaboration des composés A1-yMgyNix (3etlt;xetlt;5, 0etlt;yetlt;1, A= La, Pr, Nd) ainsi que de les caractériser d'un point de vue structural et physico-chimique (DRX, microsonde électronique, ICP) et de déterminer leurs propriétés vis-à-vis de l'hydrogène (réac tion solide-gaz et électrochimique). Durant ce travail de nouvelles phases ont été découvertes et caractérisées : les phases (A1-yMgy)5Ni19
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Madern, Nicolas. "Propriétés de sorption de l’hydrogène et mécanismes de corrosion en milieu aqueux d’alliages ABx (A = La, Sm, Y, Mg; B = Ni, Mn; 3 ≤ x < 5) pour le stockage de l’énergie". Thesis, Paris Est, 2018. http://www.theses.fr/2018PESC0105.
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L'objectif du projet est de faire émerger de nouveaux alliages de type A,MgBx pro metteurs en termes d'applications électrochimiques, notamment en substituant ou remplaçant le lanthane par d’autres terres rares comme le samarium, l'yttrium ou le gadolinium. En particulier, le projet se focalisera sur l'étude de leur comportement en corrosion en milieu fortement alcalin. Le comportement calendaire et en cyclage de ces matériaux sera analysé et l'influence du magnésium sur la corrosion de tels systèmes sera étudié. Les produits de corrosion seront identifiés conjointement par des techniques de caractérisation morphologique, élémentaire et structuraleThe goal of the project is to evidence new A,MgBx alloys with promising capacities for electrochemical application, in particular by substitution of lanthanum with other rare earth such as samarium, yttrium or gadolinium. The project will specially focus on their corrosion behavior in alkaline medium. Calendar and cycling corrosion of these alloys will be studied, as well as the magnesium influence. Corrosion products will be studied by combining morphological, elemental and structural characterization techniques
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Ramos, Aline. "Nucleation et croissance cristallines dans un verre sio::(2)-al::(2)o::(3)-li::(2)o : etude par microscopie electronique a haute resolution et absorption des rayons x". Paris 6, 1988. http://www.theses.fr/1988PA066504.
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Etude des premieres etapes de la cristallisation dans un verre du systeme sio::(2)-al::(2)o::(3)-li::(2)o(mgo) dans lequel de faibles quantites de titane et de zirconium sont introduites comme elements nucleants
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Held, Olivier. "Etude des réactions de combustion auto-entretenues par diffraction X en temps réel pour différents intermétalliques des systèmes Al-Ni-Ti : élaboration de ces mêmes intermétalliques par broyage mécanique et étude de leur cinétique de cristallisation". Nancy 1, 1999. http://www.theses.fr/1999NAN10250.
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Plusieurs compositions du diagramme de phases AI-Ni-Ti, ainsi que l'influence d'un tiers élément pour deux binaires, AlTi3 et NiTi, ont été étudiés par combustion auto-entretenue ou par broyage mécanique et cristallisation. Par diffraction X en temps réel, à l'aide du rayonnement synchrotron et d'un détecteur rapide, nous avons pu déterminer le chemin réactionnel des différentes combustions. Grâce à un thermocouple inséré dans l'échantillon et à une caméra infrarouge, nous connaissons l'évolution de la température au cours de la réaction. Par synchronisation X-IR nous pouvons attribuer à un point de l'échantillon un diffractograrnrne et une température à un moment donné. Nous avons aussi déterminé différentes conditions de broyage pour les diverses compositions, afin d'obtenir un alliage amorphe par mécanosynthèse. La cinétique de cristallisation de ces échantillons a été analysée par la méthode de Suriñach. Enfin, nous avons tenté d'appliquer le même mode opératoire que celui des réactions SHS pour la diffraction X en temps réel, afin de suivre le processus de cristallisation.
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Chenoufi, Adel. "Structure et comportement thermodynamique des alliages métastables Ni-Ag et Al-Mn". Rouen, 1988. http://www.theses.fr/1988ROUES015.
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Etude par microscopie électronique en transmission et par diffraction de rayons X de la structure des couches minces Ni/Ag obtenues par pulvérisation cathodique. Les échantillons sont amorphes et biphasés pour une teneur de 0,5% en argent. Quand la concentration croît, la structure devient microcristalline. Préparation des couches amorphes Al Mn par pulvérisation cathodique. Obtention par irradiation électronique localisée de la phase quasicristalline décagonale T. Analyse par calorimétrie différentielle à balayage du comportement thermodynamique. Etude comparative avec d'autres alliages amorphes Pd Si, Ni P
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Silva, Wanderson Santana da. "Avaliação do comportamento mecânico e tribológico de ligas Ni-Cr-Al-C". Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-20042007-173509/.
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Este trabalho traz contribuições à linha de pesquisa \'Nova Família de Ligas Baseada no Sistema Ni-Al-Cr-C Resistentes ao Desgaste em Elevadas Temperaturas\', estudando o comportamento mecânico, tribológico e a estabilidade superficial destas ligas. Esta família de ligas fundidas, denominada NICRALC - busca conjugar algumas características das superligas à base de níquel e dos ferros fundidos brancos, aliando ao comportamento mecânico anômalo do Ni3Al - aumento da resistência mecânica com a temperatura, até valores da ordem de 800°C - a uma dispersão de carbonetos de cromo de alta dureza. Desta forma, busca-se desenvolver uma alternativa às ligas ferrosas nas temperaturas acima das quais estas ligas perdem significativamente sua resistência mecânica (notadamente 600 °C), assim como uma alternativa mais econômica às ligas a base de cobalto resistentes ao desgaste, em virtude das altas cotações e instabilidades no preço deste elemento. Neste trabalho foram avaliadas as propriedades mecânicas em elevadas temperaturas (compressão e dureza), tenacidade à fratura na temperatura ambiente, comportamento tribológico (cavitação, abrasão, deslizamento e erosão) e a resistência à oxidação ao ar e à carburação em atmosfera redutora, em temperaturas elevadas, de ligas Ni-Al-Cr-C (NICRALC) fundidas. Ligas NICRALC fundidas com diferentes teores de carbono e submetidas a diferentes tratamentos tiveram seu comportamento mecânico e tribológico comparado ao comportamento do STELLITE 6 fundido, a uma liga NICRALC produzida por deposição por \'SPRAY\', a um ferro fundido branco alto cromo fundido convencionalmente e a um ferro fundido branco alto cromo depositado por \'SPRAY\'. Os ensaios de compressão confirmaram o comportamento anômalo da matriz ordenada Ni3Al. As ligas NICRALC apresentaram aumento ou manutenção da resistência ao escoamento com o aumento da temperatura de ensaio. A mesma tendência foi encontrada nos ensaios de dureza a quente. As demais ligas apresentaram tendência de queda da resistência ao escoamento e da dureza com o aumento da temperatura de ensaio. Esta tendência é mais acentuada na liga STELLITE, desta forma, as ligas NICRALC apresentaram em altas temperaturas maior resistência ao escoamento e maior dureza que o STELLITE. Os diferentes ensaios de desgaste mostraram, em geral, uma maior resistência do STELLITE em comparação com as ligas NICRALC na temperatura ambiente. Nestas condições verifica-se que a menor resistência mecânica da matriz ordenada nas ligas NICRALC é determinante para definir uma menor resistência ao desgaste na temperatura ambiente. Nos ensaios de erosão-oxidativa realizados a 600 e 800°C as ligas NICRALC mostraram perdas de massa menores que as experimentadas pelo STELLITE e pelos ferros fundidos. As ligas NICRALC com microestrutura de carbonetos mais homogênea, próxima do eutético, mostraram melhor comportamento sob desgaste abrasivo e erosivo se comparadas às ligas NICRALC 05 e 13. Os ensaios de resistência à oxidação mostraram que as ligas NICRALC são mais resistentes à oxidação que o STELLITE. Além disso, observou-se grande propensão ao destacamento dos filmes de óxidos formados nos STELLITES em temperaturas acima de 800°C. Os ensaios de resistência à carburação mostraram que no caso das ligas NICRALC ocorreu a precipitação de um depósito de grafita e, subjacente a esta, a formação de uma zona de fragmentação microestrutural, na qual se observa empobrecimento ora do Al ora do Cr, que aparentemente impede o avanço do processo. No caso do STELLITE verificou-se a ocorrência do aumento da fração volumétrica de carbonetos, típico dos casos clássicos de carburação. Os procedimentos de simulação termodinâmica utilizados indicam a necessidade de se implementar a descrição da solubilidade do carbono na fase ordenada de forma a permitir o pleno uso do software THERMOCALC no projeto e aprimoramento de ligas NICRALC.This work contributes to the research line \'New Family of High Temperature Wear Resistant Alloys based on the Ni-Al-Cr-C System\', studying the mechanical and tribological behaviour and the surface stability of these alloys. This family of foundry alloys, called NICRALC, tries to unite some of the characteristics of the Ni based superalloys and the high-chromium-white-cast-irons, associating the anomalous behaviour of the ordered intermetallic phase Ni3Al - which increases its strength with the increase of temperature - with a dispersion of hard chromium carbides. The aim is to develop an alternative to iron-based wear resistant alloys at temperatures where they loose significantly their strength, as well as substituting cobalt based high temperature wear resistant alloys, which suffer from the instability and high cost of the Co metal. The high temperature mechanical properties (hardness and compression), room temperature fracture toughness, tribological behaviour (cavitation, abrasion, sliding and erosion) and resistance to high temperature oxidation and carburization of cast Ni-Al-Cr-C (NICRALC) alloys are studied. Cast NICRALC alloys with different C contents and different heat treatments were compared with a cast STELLITE 6, a conventionally cast high chromium white cast iron, a spray formed high chromium white cast iron and a spray formed NICRALC. Mechanical tests in compression confirmed that NICRALC alloys share the anomalous behaviour of the ordered intermetallic phase Ni3Al, increasing or maintaining their yield strength with increased testing temperature. The same occurred with hot hardness tests. STELLITE and all other alloys showed loss of strength with increased testing temperatures. Thus NICRALC alloys showed higher strength and hardness than STELLITE at high temperatures. All wear tests showed a higher wear resistance of STELLITE in comparison with NICRALC at room temperature. This result can be explained by the higher matrix hardness of STELLITE at room temperature. Oxidative-erosion tests run at 600 and 800° C showed that NICRALC suffered smaller mass loss than STELLITE and the white cast irons. NICRALC alloys with more homogeneous carbide distributions (eutectic alloys) obtained the best results under severe oxidation-erosion conditions. NICRALC alloys were more oxidation resistant than STELLITE alloy, which tended to break and detach the oxide layer formed above 800°C under air. During carburization essays in a reducing atmosphere the NICRALC alloys tended to form a coke-like graphite layer, over a layer with a fragmented microstructure depleted alternatively in chromium and aluminum, which effectively stopped the advance of the process. The STELLITE alloy suffered an increase in carbide volume fraction, a classic carburizing behaviour. The thermodynamic simulation results show that it is still needed to introduce the solubility of carbon on the ordered Ni3Al phase in the model in order to be able to fully calculate the NICRALC phase diagrams.
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Pedra, Pablo Pedreira. "Estudo das propriedades estruturais e magnéticas do sistema Cu1-xMxO (M = Fe, Ni, Al e Zn)". Universidade Federal de Sergipe, 2011. https://ri.ufs.br/handle/riufs/5330.
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Conselho Nacional de Desenvolvimento Científico e TecnológicoIn this work were obtained of Cu1-xMxO (M = Fe, Ni, Al e Zn, for 0 ≤ x ≤ 0,1 samples, using the co-precipitation method. These samples were studied using different techniques of characterization structural and magnetic. X-ray diffraction (XRD) results added to the Rietveld refinement analysis of the x-ray powder diffraction data shows that all samples present monoclinic the same structure of CuO with space group C2/c. The magnetization measurements as function of temperature (MvsT) show a fast suppress of TN for Fe-doped CuO samples, in contrast with (Ni, Zn and Al)-doped CuO. Synchrotron radiation XRD data at low temperature performed with show that the Cu0,9Fe0,1O and Cu0,9Ni0,1O samples present slow changes in the cell parameters, which it can be associated with the magnetic transition. Although the X-ray absorption (XAS) measurements performed in Cu K-edge show a variation in the density of unoccupied state in the p sublevel, appreciable changes in the local structure of these ions ban not be confirmed. On the other hand, measurements at the doping K and L2,3-edges confirm the existence of Ni2+ ions and oxygen vacancies and/or defect in your structure, already measurements performed in Cu0,9Fe0,1O sample shown the presence of Fe+2/Fe+3 mixed valence.
Neste trabalho foram obtidas amostras de Cu1-xMxO (M = Fe, Ni, Al e Zn) usando o método químico de co-precipitação. Estas amostras foram estudadas por diferentes técnicas de caracterização estrutural e magnética. Resultados de difração de raios X (DRX) associados às análises de refinamento Rietveld confirmam que todas as amostras de CuO dopadas com Fe, Ni, Al e Zn apresentaram estrutura cristalina similar a estrutura monoclínica do CuO puro, pertencente ao grupo espacial C2/c. As medidas de magnetização em função da temperatura (MvsT) mostram uma rápida supressão da temperatura de Néel (TN) de 210 K para 65 K, na amostras de CuO dopadas com 10% de Fe, em contraste com os sistema dopado com Ni, Zn e Al. Resultados de DRX em baixa temperatura usando radiação síncrotron indicam suaves alterações no parâmetro de rede das amostras de Cu0,9Fe0,1O e Cu0,9Ni0,1O, os quais podem estar associados com a transição magnética. Embora as medidas de absorção de raios X realizadas na borda K do Cu, antes e depois da TN, mostrarem uma variação na densidade de estado desocupado no subnível p, não se verificaram mudanças apreciáveis na estrutura local destes íons. Por outro lado, as medidas de absorção na borda K e L2,3 do dopante confirmam a existência de íons de Ni com estado de oxidação +2 e vacância de oxigênio e/ou defeitos na estrutura monoclínica do CuO dopado com Ni. Já nas medidas realizadas na amostra de Cu0,9Fe0,1O mostra a presença de valência mista de Fe+2/Fe+3 neste composto.
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OLIVEIRA, Alexandre Miranda de. "Síntese e caracterização de compostos do sistema x/2 Al²O³-x/2 Y²O³ (100 - x) SiO² (x=10,20,30,40 e 50) dopados com Er³+ para aplicação em fotônica". Universidade Federal de Goiás, 2010. http://repositorio.bc.ufg.br/tede/handle/tde/809.
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Previous issue date: 2010-12-15This work is to study the crystallization of compounds in the form of post system alumina-yttria-silica prepared by sol-gel mixed methodology and Pechini. Powders (x / 2) Y ² ³ - (X / 2) Al ² O ³ - (1-x) SiO ² (x = 0.1 0.2, 0.3, 0.4 and 0.5 mol) were doped with erbium prepared and characterized. The physical properties of composite SiO ² ¹ YO-, 5 - AlO ¹, 5 were studied by x-ray diffraction, FTIR spectroscopy, thermogravimetry, differential thermal analysis and photoluminescence measurements. It was possible to maintain the amorphous compositions at high temperatures, no crystallization below 900 ° C and the formation of phase Y ² ² O7 Si at 1100 ° C. We obtained a reasonable life time of some compositions treated at 1000 ° C. We observed the emission of green upconversion to excite the samples with high power laser. All synthesized samples exhibit photoluminescence emission and have maximum emission at 1530 nm with a width of ~ 47nm. This broad issue is a desirable property for amplifiers used in systems division multiplexing wavelengths (WDM) and suggests that Er ³ + ions are hosted in the amorphous phase.
Neste trabalho estudo-se a cristalização de compostos na forma de pós do sistema alumina-ítria-sílica preparados pela metodologia mista sol-gel e Pechini. Pós de (x/2) Y²O³-(X/2) Al²O³-(1-x) SiO² (x=0,1 0,2, 0,3, 0,4 e 0,5 em mol) dopados com érbio foram preparados e caracterizados. As propriedades físicas dos composto de SiO²-YO¹,5- AlO¹,5 foram estudadas por difração de raios-x, espectroscopia FTIR, termogravimetria, análise térmica diferencial e medidas de fotoluminescência. Foi possível manter as composições amorfas a altas temperaturas, não houve cristalização abaixo de 900° C e a formação da fase Y²Si²O7 a 1100 °C. Obtivemos um tempo de vida razóavel de algumas composições tratadas a 1000°C. Observamos a emissão verde de upconversion ao excitar as amostras com laser de alta potência. Todas as amostras sintetizadas apresentam emissão fotoluminescente e possuem máximo de emissão em 1530 nm com largura a meia altura de ~47nm. Essa emissão larga é uma propriedade desejável para amplificadores usados em sistemas de multiplexação por divisão de comprimentos de onda (WDM) e sugere que os íons Er³+ estão hospedados na fase amorfa.
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Neto, Ricardo Mendes Leal. "Síntese por combustão do NbAl3 e de ligas do sistema Nb-Ni-Al". Universidade de São Paulo, 1998. http://www.teses.usp.br/teses/disponiveis/85/85132/tde-25062012-102602/.
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O NbAl3 e algumas ligas intermetálicas do sistema Nb-Ni-AI foram sintetizadas por combustão a partir dos pós de seus elementos constituintes. O efeito de variáveis de processo, como o tamanho de partícula dos pós, a composição química, a pressão de compactação, o tratamento de desgaseificação e a taxa de aquecimento, foram investigados na síntese do NbAl3 na forma de pastilhas cilíndricas. A síntese de ligas do sistema Nb-Ni-AI foi realizada a partir de misturas com as composições Nb10Ni70AI, Nb20Ni65AI e Nb30Ni60AI. A microestrutura das amostras reagidas foi caracterizada por microscopia óptica, microscopia eletrônica de varredura, EDS e difração de raios-X (método de Rietveld). Foram obtidas pastilhas de NbAl3 com 98,5 % da densidade teórica, superior ao valor encontrado na literatura (95%), mediante o controle de variáveis de processo. Nas pastilhas contendo níquel, a combustão ocorreu nas pastilhas de todas as composições. Fases metaestáveis, presentes na microestrutura das pastilhas baitas de reação, foram transformadas após tratamento térmico, originando ligas trifásicas com diferentes concentrações de fases (NbAl3, NiAI e NbNiAI), conforme a composição inicial do compactado. Algumas propriedades mecânicas de amostras brutas de reação e tratadas termicamente foram determinadas pela técnica da impressão (microdureza e tenacidade). Os resultados obtidos são comparáveis aos da literatura, salvo algumas discrepâncias atribuídas a processos de fabricação distintos. As etapas de reação da síntese do NbAl3 e de ligas Nb-Ni-AI foram posteriormente investigadas mediante interrupção da reação durante sua propagação ao longo de barras paralelepipédicas compactadas. Verificou-se que a síntese do NbAl3 ocorre pela dissolução de nióbio no alumínio fundido, seguida da precipitação do NbAl3. Nas amostras contendo níquel, a síntese ocorre em dois estágios: no primeiro estágio formam-se o Ni2Al3 ou o NiAl3, em quantidades relativas dependentes da composição geral. As reações deste primeiro estágio podem disparar as reações do segundo estágio, referentes à síntese do NbAl3.NbAl3 and Nb-Ni-AI intermetallic alloys have been obtained by pressureless combustion synthesis from elemental powders. The effects of process variables as powder particle size, composition, compaction pressure (green density), degassing treatment and heating rate on the combustion (thermal explosion mode) of NbAl3 cylindrical pellets were studied. Combustion synthesis of Nb-Ni-AI alloys was performed on powder mixtures with nominal compositions Nb10Ni70AI, Nb20Ni65AI and Nb30NI60AI. The microstructure of reacted samples was characterized by optical microscopy, scanning electron microscopy, EDS and X-ray diffraction (Rietveld method). It was shown that careful control of the processing conditions allowed near full (98,5%) dense pellets of NbAl3. In the nickel containing pellets, reaction occurred for all the compositions investigated. Metastable phases were seen to be present in the as reacted pellets, which were transformed after a heat treatment, producing a three phase alloy (NbAl3, NiAI and NbNiAI) with different phase concentrations, depending on the initial compact composition. Some mechanical properties, like microhardness and tenacity were measured by microidentation technique on the as reacted and heat-treated samples. The results are comparable with the literature, excepted for some discrepancies caused by different fabrication processes. The reaction sequence for both cases (NbAl3 and Nb-Ni-AI alloys) was further investigated by DSC analysis and also by interrupting the reaction during its propagation along compacted parallelopipedal bars. It was found that the NbAl3 synthesis occurs through niobium dissolution in molten aluminum and precipitation of NbAl3. In the nickel containing samples, synthesis occurs as two-stage reaction: Ni2Al3 or NiAl3 are formed in the first stage, with relative amounts depending on the general composition. This first stage reaction can trigger the second one, related to the formation of NbAl3.
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Dang, Ning. "3d visualization for microstructure characteristics and damage evolution in dual phase titanium alloy". Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEI053.
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Le titane et ses alliages, qui possèdent des propriétés intégrées, notamment une faible densité, une résistance spécifique élevée et une excellente résistance à la corrosion, sont des "bêtes de somme" dans le domaine des industries modernes. Au cours des dernières années, avec le développement des technologies industrielles, nous avons imposé des exigences strictes aux propriétés des composants fabriqués en alliages de titane dans des environnements difficiles. Comment explorer d'autres propriétés potentielles dans les alliages de titane? Une telle question a attiré les yeux des chercheurs. Par conséquent, afin de révéler de manière intensive le micromécanisme des dommages et des fractures pour les alliages de titane, il est tout à fait nécessaire de renforcer nos connaissances sur les caractéristiques de la microstructure et les caractéristiques d'évolution des dommages, en particulier sur l'interaction entre les caractéristiques de la microstructure et le développement des vides. Dans cette thèse, visant à la variation des morphologies de la microstructure au cours du développement des dommages, basée sur une approche de tomographie par rayons X (tomographie à rayons X), une méthodologie intégrée comprenant une expérience in situ et une simulation CP (Crystal Plasticity) a été mise en œuvre pour morphologies de microstructure et comportement de nucléation / propagation de vide de l'alliage Ti-6Al-4V (TA6V) au cours de l'évolution des dommages. En outre, avec l’aide d’une modélisation RVE (élément de volume représentatif) réaliste basée sur la microstructure et d’une simulation de déformation subséquente, combinant post-mortem par SEM / EBSD, nous avons révélé le mécanisme de développement des dommages en analysant de manière approfondie les caractéristiques de fracture. Enfin, la corrélation entre microstructure et évolution est discutée sur la base de simulations et d’expériencesTitanium and its alloys, which have integrated properties including low density, high specific strength and excellent corrosion resistance, are "workhorses" in the field of modern industries. In recent years, with the development of industrial technologies, we have strict requirements on the properties of components made by titanium alloys in severe environment. How to explore further potential properties in titanium alloys? Such question has attracted researchers' eyes. Therefore, in order to reveal the micro-mechanism of damage and fracture for titanium alloys intensively, it is quite necessary to enhance our knowledge on the microstructure characteristics and damage evolution features, particularly on the interplay between microstructure characteristics and voids development. In this thesis, aiming at the variation of microstructure morphologies during damage development, based on X-ray computed tomography (X-ray CT) approach, an integrated methodology containing in situ experiment and CP (Crystal Plasticity) simulation was implemented to focus on the microstructure morphologies and void nucleation / propagation behavior of Ti-6Al-4V (TA6V) alloy during damage evolution. Besides, with the help of realistic microstructure-based RVE (Representative Volume Element) modeling and subsequent deforming simulation, combining with post-mortem by SEM / EBSD, we have revealed the mechanism for damage development by severely analyzing the fracture features. Finally, the correlation between microstructure and evolution is discussed on the basis of simulations and experiments
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Chassagne, Francis. "Etude de l'ordre à courte distance dans la solution solide gamma Ni-Al". Paris 6, 1986. http://www.theses.fr/1986PA066098.
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Etude par mesures quantitatives de diffusion en diffraction de rayons X de l'état de l'ordre local dans les alliages binaires Ni-10,5 et 7,3% at Al. Description de la méthode d'étude. Calcul des potentiels d'interaction de paires par comparaison de l'intensité d'ordre à courte distance avec la susceptibilité du modèle de champ moyen de paires sur un réseau cubique à faces centrées à champ non nul. Détermination de l'énergie d'interface précipitée.
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Ångström, Jonas. "Hydrogen absorption/desorption properties of the Sc(AlxNi1-x)2 system". Thesis, Uppsala universitet, Oorganisk kemi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-159372.
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Sc(AlxNi1-x)2 is a pseudobinary C14 Laves phase and a potential interstitial hydrogen storage material or anode in a Ni-MH battery. A previous study showed that Sc1Al1Ni1 can store hydrogen reversibly; both interstitially and trough decomposition into ScH2 and AlNi. It is also known that the exact composition is very important for the hydrogen storage properties of pseudobinary Laves phases. This thesis work is aimed at synthesising Sc(AlxNi1-x)2 and study the effect of the Ni/Al ratio on the hydrogen absorption/desorption process as well as the interstitial storage capacity. Compositions with high nickel content had the highest capacity (at least 0.67wt% for ScAl0.66Ni1.34) and ones with high aluminium content had the lowest total storage capacity (0wt% for ScAl1.28Ni0.62). The former composition was also shown to absorb and desorb hydrogen during multiple cycles. Desorption of interstitial hydrogen from ScAl0.66Ni1.34 requires 4.6kJ/mol in activation energy.
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Martins, Juliana de Paula. "Evolução da microestrutura e da textura durante o processamento de chapas da liga Al-Mn-Fe-Si (3003) produzidas por lingotamento contínuo: um estudo comparativo com o processo semi-contínuo". Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-31012006-124433/.
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A principal motivação para o desenvolvimento do presente projeto de doutorado foi comparar as microestruturas e texturas resultantes da liga de alumínio 3003 obtida por lingotamento contínuo e semicontínuo. O processo roll caster (lingotamento contínuo em cilindros) tem sido crescentemente utilizado na indústria de laminação de alumínio. Produtos que antes sofriam altos graus de deformação durante seu processamento são hoje obtidos nas dimensões próximas da espessura final. Com o intuito de entender este processo relativamente novo, as microestruturas e as texturas (macrotextura e microtextura), ao longo da espessura, das chapas produzidas por lingotamento contínuo e por lingotamento semicontínuo (placas fundidas com 250 mm de espessura, seguido de homogeneização e laminação a quente) foram analisadas. Foi possível constatar que os materiais provenientes dos dois processos diferem bastante e que ao longo da espessura também há grandes diferenças. Foi possível observar que durante o processamento roll caster há considerável deformação plástica, com a formação de células de discordâncias e subgrãos. Foi possível observar, também, que a microestrutura, a morfologia e o tamanho de grão, da amostra caster bruta de fundição são mais homogêneos que na amostra laminada a quente. As duas chapas, a laminada a quente e a obtida por lingotamento contínuo, exibem forte gradiente de textura ao longo da espessura. A textura predominante nos dois processos, ao longo da espessura, é a do tipo latão {011}. A evolução da textura do material proveniente do processo roll caster também foi caracterizada após laminação e posterior recristalização, revelando a presença de componentes típicas de laminação e de recristalização de alumínio. Após laminação a frio com redução de 91% e posterior tratamento térmico de 400°C por 1 h, a chapa proveniente do processo caster apresentou uma textura de recristalização caracterizada pela presença da componente cubo (recristalização) somada à parcela de textura de deformação. No caso do alumínio e suas ligas, sabe-se que esta textura proporciona os melhores resultados para minimizar o efeito de orelhamento durante a estampagem. Outro ponto relevante do trabalho foi o aperfeiçoamento da técnica de extração de precipitados para a liga 3003, uma vez que, a extração de precipitados em ligas de alumínio é especialmente problemática, pois a maioria das partículas presentes dissolve-se até mais facilmente que a matriz de alumínio. Algumas técnicas foram testadas: 1. dissolução química em solução de iodo em metanol; 2. dissolução eletrolítica em solução de ácido benzóico e hidroxiquinolina em clorofórmio e metanol; 3. dissolução eletrolítica em solução de ácido perclórico, butil glicol, álcool etílico e água; 4. dissolução química em solução de fenol. A técnica que apresentou melhores resultados foi a dissolução química com fenol, onde foi possível separar os precipitados da matriz alumínio. Com o auxílio desta técnica foi possível analisar as transformações de fase do composto intermetálico Al6Mn durante tratamentos térmicos. Obtiveram-se dados da completa transformação da fase Al6Mn em alfa-AlMnSi, também conhecida na literatura como, transformação "six to alfa". A precipitação e os precipitados desempenham um papel importante na cinética de recristalização e no tamanho de grão final. Para se entender este comportamento, comparou-se uma chapa que sofreu tratamento térmico antes da laminação com outra chapa que foi laminada no estado bruto de fundição. Os resultados revelaram que a recristalização foi retardada na amostra, inicialmente, bruta de fundição. A precipitação ocorreu simultaneamente com a recristalização, com isso, os dispersóides precipitaram preferencialmente na microestrutura deformada, em subcontornos ou nas discordâncias isoladas, levando a um considerável atraso no rearranjo das discordâncias e na nucleação da recristalização.The main reason for the development of this PhD Thesis was to compare the microstructures and textures of the 3003 aluminum alloy produced from continuous and semi-continuous casting processes. The roll caster process (continuous casting) has been increasingly used in the aluminum industry. Products usually obtained by means of heavy rolling operations in the past are nowadays obtained with dimensions close to the final ones using the roll caster technology. To understand this new process, microstructures and textures (macrotexture and microtexture) along the thickness of the sheet produced by continuos casting and semi-continuous casting (plates with 250 mm thickness, followed by homogenization and hot rolling) have been investigated. It was possible to verify that materials coming from these two processes did differ each other a lot mainly across the thickness. During roll casting the plastic deformation was large enough to promote the formation of dislocation cells and subgrains. It was also possible to notice that the microstructure, morphology, and grain size from as-cast sample are more homogenous than the ones found in hot rolled samples. Both the sheets obtained by hot rolling and continuous casting have shown a strong texture gradient across the thickness. The predominant texture in both processes is the Brass component {011} . The texture evolution from sheets obtained by roll casting was also determined after rolling and subsequent recrystallization. It shows the presence of typical components of rolling and recrystallization of aluminum. After 91% cold rolling and subsequent recrystallization at 400°C for 1 h, the cube component (recrystallization texture) and the deformation texture were observed. It is well known that this texture minimizes earing effects during deep drawing of aluminum products. Another relevant point in this work was the development of the technique for the extraction of precipitates for the aluminum 3003 alloy. The extraction of precipitates extraction is particularly problematic in aluminum because most of the particles tend to dissolve more readily than the aluminum matrix. Some of the techniques performed are the following: 1. chemical dissolution with iodine in methanol solution; 2. electrolytic dissolution with benzoic acid and hydroxyquinoline in chloroform and methanol; 3. electrolytic dissolution with perchloric acid, butyl-glycol and ethanol; 4. chemical dissolution with phenol solution. Chemical dissolution with the phenol solution was the technique that provided the best results. It was possible to separate precipitates from the aluminum matrix. With this extraction technique it was possible to analyze phase transformations of the intermetallic compound Al6Mn during heat treating of this alloy. The phase transformation of the Al6Mn compound into alfa-AlMnSi, also known as 6-to-alfa transformation, could be followed in detail by means of this technique. Precipitation plays an important role in the recrystallization kinetics and final grain size. Therefore, to understand this behavior, the roll cast aluminum alloy was cold rolled from two distinct starting conditions: as-cast and heat-treated (homogeneized) conditions. It was shown that recrystallization was delayed in the sheet rolled from the as-cast condition. Precipitation has occurred simultaneously with recrystallization, in such a manner that dispersoids did precipitate in the deformed microstructure, preferentially, at subgrain boundaries or at free dislocations. As a result, the rearrangement of the dislocations and further recrystallization nucleation has been significantly retarded.
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Montet-Berthéas, Yaël. "Elucidation des mécanismes d'action des hydrogénases à Ni-Fe : étude de l'hydrogénase de Desulfovibrio fructosovorans et de ses mutants par cristallographie des rayons X". Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10184.
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Les hydrogenases sont des enzymes capables de catalyser de facon reversible l'oxydation de l'hydrogene : h#2 2h#+ + 2e#. La structure a 2,85a de resolution de l'hydrogenase a ni-fe de desulfovibrio gigas a revele un site actif tres enfoui dans la grande sous-unite et contenant un atome de ni et un autre atome metallique, probablement du fe coordine a trois ligands diatomiques non-proteiques. Elle a egalement confirme la presence de trois centres fe-s dans la petite sous-unite, dont l'agencement suggere un chemin pour les electrons entre le site actif et la surface. Au cours de ce travail, nous avons tente de comprendre le role de ce site actif complexe et d'analyser le transfert des electrons et de l'hydrogene dans la proteine. Parce qu'un programme de mutagenese dirigee etait entrepris sur l'hydrogenase de d. Fructosovorans (65% d'identite de sequence avec d. Gigas), la premiere etape a consiste a resoudre la structure native de cet enzyme. Puis, pour comprendre le role de l'agregat 3fe4s situe entre les deux 4fe4s et presentant un potentiel tres superieur, nous avons etudie le mutant p238c correspondant a une mutation ponctuelle proche de ce centre. Sa structure a 3a a permis de montrer la transformation du centre 3fe4s en 4fe4s. Cependant, la cinetique de l'enzyme mute n'est que tres faiblement affectee, ce qui suggere que l'etape limitante de la reaction n'est pas le transfert d'electrons. Nous avons egalement resolu la structure a 1,81a du mutant s499a, qui concerne un residu engage dans deux liaisons hydrogene avec un ligand du fe au site actif. La mutation a donc rompu une des liaisons h, mais aucune variation infrarouge ou structurale n'a pu etre observee. La haute resolution a toutefois permis d'obtenir une image extremement precise du site actif. Enfin, nous avons etudie l'accessibilite des gaz au site actif des hydrogenases. La structure de d. Gigas a revele l'existence de canaux hydrophobes reliant la surface au site actif. La diffusion de xenon dans des cristaux de proteine a montre que celui-ci se fixait tres precisement le long de ces canaux. Des simulations par dynamique moleculaire de diffusion de gaz ont confirme que les molecules gazeuses diffusent toujours au travers de ces canaux. Ces resultats suggerent fortement un role fonctionnel pour ces canaux, en facilitant le transfert de l'hydrogene moleculaire.
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Kernavanois, Nolwenn. "Blocage du moment orbital et hybridation des électrons f : étude par absorption et diffusion de rayons-X et diffraction de neutrons de composés à base d'uranium et de cérium". Université Joseph Fourier (Grenoble), 2000. http://www.theses.fr/2000GRE10114.
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Au cours de ce travail, nous avons utilise le dichroisme magnetique circulaire de rayons-x (xmcd), la diffusion magnetique compton de rayons-x de haute energie (mcs) et la diffraction de neutrons pour l'etude des proprietes magnetiques de plusieurs composes a base d'uranium et de cerium : us, uni 2al 3, uge 2, cefe 2 et les multicouches u-as/co. Des experiences de mcs et de xmcd aux seuils m 4 , 5 de l'uranium ont ete realisees sur us. L'association de ces resultats avec ceux precedemment obtenus par diffraction de neutrons polarises permet la separation des contributions d'orbite et de spin des moments localises et diffus. Nous comparons nos resultats avec ceux publies pour use et ute. Une etude du fermion-lourd supraconducteur antiferromagnetique uni 2al 3 dans sa phase paramagnetique a ete effectuee par diffraction de neutrons polarises et par xmcd aux seuils u-m 4 , 5. Les analyses des donnees mesurees par diffraction de neutrons, indiquent la presence d'un moment induit sur les sites de ni. Nos resultats sont compares a ceux publies sur upd 2al 3. La structure magnetique de uge 2 a ete etudiee par diffraction de neutrons non-polarises. Des mesures de diffraction de neutrons polarises et de xmcd ont egalement ete effectuees et ont permis de determiner les valeurs des moments magnetiques d'orbite et de spin sur u. Les profils magnetiques compton de cefe 2 et lufe 2 ont ete mesures. La comparaison de tous les resultats disponibles sur cefe 2 traduit des problemes qu'il semble raisonnable d'attribuer a la qualite des echantillons etudies. Pour finir, des mesures xmcd aux seuils u-m 4 , 5 dans les multicouches u-as/co, ont mis en evidence un moment sur u a temperature ambiante, induit par couplage d'echange avec co. Ce travail souligne l'importance d'associer differentes techniques et de comparer les resultats de composes parents pour la comprehension des processus d'hybridation.
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Srinivasan, Dheepa. "Phase Evolution, Thermal Stability And Hardness Of Melt Spun Nanocrystalline Al-X-Zr (X=Si,Cu,Ni) Alloys". Thesis, 1999. https://etd.iisc.ac.in/handle/2005/1527.
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Srinivasan, Dheepa. "Phase Evolution, Thermal Stability And Hardness Of Melt Spun Nanocrystalline Al-X-Zr (X=Si,Cu,Ni) Alloys". Thesis, 1999. http://etd.iisc.ernet.in/handle/2005/1527.
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Shu-KuanLin i 林書寬. "Surface Studies of 3-Chloro-1-propanol/Ni(111) and C6-xNx(x=0-3)/Cu(100)". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/53120013283590738239.
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碩士國立成功大學
化學系碩博士班
100
Thermal chemistry of 3-chloro-1-propanol on Ni(111) Temperature-programmed reaction/desorption and X-ray photoelectron spectroscopy have been employed to investigate the thermal reactions of ClCH2CH2CH2OH on Ni(111) in an ultra-high vacuum system. At 100 K, a part of adsorbed ClCH2CH2CH2OH molecules decompose by breaking the C-Cl and O-H bonds. At a low coverage, decomposition of ClCH2CH2CH2OH leads to the formation propane、propene and cyclopropane below 140 K. At higher coverages, no hydrocarbon products are found, instead, acetone、3-chloropropene and ethene are the reaction products below 300 K. In addition, H2 and CO desorb above 300 K. Theoretical studies of C6-xNx(x=0-3)/Cu(100)：adsorption structure and formation energy Theoretical calculations for the structures and formation energies of C6-xNx clusters on Cu (100) have been performed. For a specific cluster, linear-chain structure is more stable than ring form. Terminal carbon atoms of linear chains are perferentially bounded at hollow sites. The six atoms in the chain tends to be located in a plane normal to the surface, due to the formation of delocalized π system. N-substitution results in a decrease of chain stability. Activation energies of the transformation between linear and cyclic structures are also obtained in this study.
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Jie-NingLiou i 劉介寧. "Microwave Dielectric Properties and Applications of LTCC Using Li2X2(MoO4)3 (X=Co,Ni)". Thesis, 2019. http://ndltd.ncl.edu.tw/handle/xqf3qx.
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Vamsi, Koruprolu Venkata. "Planar Fault Energies in L12 Compounds". Thesis, 2017. http://etd.iisc.ac.in/handle/2005/4254.
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High temperature metallic structural materials, such as Ni-base superalloys owe their strength to a two-phase microstructure consisting of an fcc matrix strengthened by intermetallic A3B type precipitates. The performance of these alloys derives from the exceptional high temperature strength of the L12-ordered A3B precipitate, which in turn is strongly influenced by planar faults created when the precipitate is sheared. In this context, the broad goal of this work is to understand the role of composition on planar fault energies in A3B compounds with L12 structure. Towards this aim, electronic structure calculations using density functional theory (DFT) was used to evaluate fault energies through direct simulations of faults and though indirect means involving analytical models. In the first part of the thesis, the effect of composition on the planar fault energies, elastic anisotropy, deformation modes and yield strength anomaly were explored in five pseudo-binaries (Ni, Co)3(Al,X) compositions of γ' (L12), where X = Ti, Ta, W, Ni. It was observed fault energies and deformation modes are sensitive to composition. The results are in good agreement with literature and can provide explanations for the deformation behaviour of both (Ni)3(Al, X) and Co3(Al,W). Though the results are encouraging, the above DFT calculations of fault energies are time-consuming, highlighting the need for high throughput models. In the second part of the thesis, such a model was developed to estimate these energies in well-known and novel A3B compositions. The new model treats the planar fault as a diffuse interface and allows estimation of fault energy in terms of energy of geometrically close packed structures with the same A3B composition and a bonding environment akin to that of the fault. The proposed model was used to predict energies of different superlattice faults in over 40 A3B compounds. The model was found to be highly accurate even without use of fitting parameters and has a fifteen-fold computational advantage over direct simulation. The model was extended to novel A3B compounds based on Pt3X, Rh3X and Ir3X where data is presently lacking. Despite the efficiency of the model, it had limitations in predicting fault energies in non-binary compositions. To account for this, in the last section of this thesis, a novel quasi-chemical model incorporating the far-field composition effects, was developed. The model was validated for several pseudo-binary systems and it was found that be more accurate than the diffuse interface model. The two models were then extended to predict fault energies in binary L12-ordered A3B compounds at high temperatures, complex multicomponent L12-ordered A3B compounds, and binary D019-ordered A3B compounds.
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Wei, Ching-Yi, i 魏景怡. "Structure and magnetic properties of an iron (III) spin crossover compound: [Fe(3-OMe-salMen)2]2[Ni(mnt)2]•x CH3CN". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/91644940644674903346.
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碩士國立臺灣大學
化學研究所
96
A cationic Fe(III) complex, [Fe(3-OMe-salMen)2]+, forms crystals with Ni(II) complex anion [Ni(mnt)2]2- in three forms in formula of [Fe(3-OMe-salMen)2]2 [Ni(mnt)2] • xCH3CN, (3-OMe-salMen = 2-({[2-(methyl-amino)ethyl]imino} methyl)-3-methoxyphenol; mnt = maleonitriledithiolate) where x =2 is designated as form A; x = 0 for other two forms (B and C). All three crystal structures are characterized by single crystal diffraction method. A belongs to triclinic space group, Pī, with cell parameters a = 9.402(2), b = 10.476(2), c = 16.636(3) Å, α = 87.17(3), β = 77.38(3) and γ = 75.21(3) º; B also belongs to triclinic space group, Pī, with cell parameters a = 10.519(2), b = 10.797(2), c = 13.698(3) Å, α = 100.16(3), β = 100.48(3) and γ = 99.80(3) º; C belongs to monoclinic space group, P21/n, with cell parameters a = 9.5747(19), b = 24.916(5), c = 12.404(3) Å, α = 90, β = 102.52(3) and γ = 90 º. The cation is an octahedrally coordinated (N4O2) iron(III) complex; the anion is a square planar nickel(II) complex. Iron(III) is coordinated by two tridentate ligands, 3-OMe-salMen. According to magnetic measurement, the iron(III) (d5) in A is at the low spin state (LS, S = 1/2) in the temperature range of 5~350 K, while B and C display a gradual spin transition between high spin (HS, S = 5/2) (6A1g) and low spin state (LS, 2T2g) with T1/2 ~ 290 K and 120 K, respectively. Based on the TGA, SQUID and in-situ powder XRD results, the solvent molecule CH3CN in A can be removed by heating at temperature higher than 360 K; meanwhile the spin state of iron(III) changes from LS to HS. B can be obtained from A by removing all the solvent molecules, CH3CN, from the lattice; however the process is completely reversible and accompanied with the structure change as evidenced by the in-situ X-ray powder diffraction. Furthermore, C can be obtained from A during the solvate extraction process with an external pressure. In contrary to the reversible transformation between A and B, the transformation from A to C is irreversible, and the phase transition from B to C is not found. The crystal packing of complex A, B and C are analogously arranged by alternate layers of complex cations and anions. The cations in complex A and B form dimer like pairs via π-π interaction of the phenyl rings of the ligands. As for C, such dimer like pairs no longer exist, the packing is quite different from those of A and B. It is plausible that the different molecular packing may cause the significant shift in magnetic transition temperature.