Entre 2003 et 2010, dans la région centrale nommée X de la catacombe des Saints Pierre-et-Marcellin à Rome, a été découvert et en partie fouillé un ensemble de sépultures plurielles inédites (Ier-IIIe s. ap. J.-C.) contenant plusieurs centaines d’individus, lesquels ont été inhumés selon des pratiques funéraires singulières à la suite d’un épisode de surmortalité de nature probablement épidémique. Pour appréhender l’histoire de vie (alimentation et mobilité) de ces défunts et rediscuter sur la base d’éléments nouveaux certaines hypothèses préalablement établies, nous avons mené dans le cadre de ce travail une approche archéo-biogéochimique multi-proxy (14C, δ13C, δ15N, δ18O et 87Sr/86Sr) et multi-tissulaire (émail, os, cheveu) sur un échantillon de 130 individus issus de six différentes chambres. Nous avons dans un premier temps vérifié l’intégrité biochimique et isotopique des fractions minérales (phases carbonatées) et organiques (phases collagénique et kératinique) des échantillons à partir d’indicateurs classiques mesurés en routine (%Col, %C, %N, C/N, PCO2 et PCO2/Masse) et par spectroscopie IRTF (IRSF, CO3/PO4 et AmideI/PO4) et par une approche innovante consistant en des datations 14C sur couples collagène-apatite pour valider le signal isotopique des fractions minérales. Nos résultats mettent en évidence des différences extrêmes de préservation de toutes les phases. La trajectoire diagénétique des échantillons n’est toutefois pas aléatoire mais dépendante des conditions environnementales et taphonomiques différant entre les petites et les grandes chambres. En outre, nous avons pu démontrer qu’en dépit de fortes recristallisations et d’échanges isotopiques avec l’environnement sépulcral, les phases carbonatées possèdent un signal isotopique biogénique non altéré. Nous avons dans un second temps reconstruit les régimes alimentaires des individus en nous appuyant sur des référentiels de comparaisons robustes ainsi que divers modèles interprétatifs (mono-proxys versus multi-proxys ; qualitatifs versus quantitatifs), lesquels ont été dans certains cas adaptés au besoin de notre étude. D’une façon générale, nos résultats montrent que l’essentiel des individus a eu accès à un régime alimentaire type fondé sur la triade Céréales C3/Viande C3/Poisson marin. Ce régime alimentaire type n’est toutefois pas exclusif, certains individus (n = 13) ayant consommé de façon occasionnelle d’autres catégories de ressources tels que du poisson dulcicole ou des céréales C4. Nos résultats révèlent que les changements d’alimentation au cours de la vie sont relativement limités. Par ailleurs, cette population se singularise sur un plan strictement alimentaire au regard des autres populations contemporaines romaines pour lesquelles des valeurs isotopiques sont publiées. Nous avons dans un troisième temps étudié les schémas de mobilité des individus en nous fondant sur une approche rigoureuse de nos données et sur des référentiels de comparaison les plus exhaustifs possible ainsi qu’en tenant compte de biais ordinairement éludés (faits culturels, influence du climat et erreurs associées aux équations de conversion). Nos résultats mettent en lumière qu’a minima 23 % (n = 30) des individus étudiés sont migrants. Ces derniers ne se distinguent toutefois pas de par leur alimentation des résidents romains. Nous avons pu montrer en outre que ces migrants ont eu des trajectoires de vie complexes et hétérogènes et que trois schémas de mobilité distincts les caractérisent. Notre population ne se différencie pas en termes de taux de migrants des autres populations romaines pour lesquelles des données isotopiques sont disponibles. Elle se distingue en revanche par son cosmopolitisme avec des origines pour les migrants des plus diverses : Europe, Afrique, Arabie et Asie mineure [...]. / An assembly of unpublished complex plural burials (1st-3rd cent. AD.) was discovered and partially excavated, between 2003 and 2010 in the central region called X of the catacomb of Saints Peter and Marcellinus in Rome. It contains several hundred individuals which were buried according to uncommon funeral practices following a mortality episode of likely epidemic nature. To understand the life history (diet and mobility patterns) of these deceased and to discuss again certain assumptions previously established on the basis of new evidences, we have as part of this work conducted an archaeo-biogeochemical multi-proxy (14C, δ13C, δ15N, δ18O et 87Sr/86Sr) and multi-tissue (enamel, bones, hair) approach on a sub-sample of 130 individuals coming from six different chambers. At the outset, we tested the biochemical and isotopic integrity of mineral (carbonate phases) and organic fractions (collagen and keratin phases) samples from conventional indicators measured in routine (%Col, %C, %N, C/N, PCO2 et PCO2/Mass), by FTIR spectroscopy (IRSF, CO3/PO4 and AmideI/PO4) and by an innovative approach consisting of 14C dating on collagen-apatite to validate the isotopic signal of mineral fractions. Our results highlight extreme differences of preservation of all phases. Diagenetic trajectory of samples is however not random but dependent on environmental and taphonomical conditions which differ between small and large chambers. Furthermore, we have been able to demonstrate that, despite strong recrystallization and isotopic exchanges with the sepulchral environment, carbonated phases have an unaltered biogenic isotopic signal. Secondly, we rebuilt the diets of individuals based on robust comparisons repositories and various interpretative models (mono-proxy versus multi-proxies; qualitative versus quantitative) which were, in some cases, adapted to the needs of our study. In general, our results show that most of the individuals had access to such a type diet based on the triad Cereals C3/Meat C3/Marine fish. This type diet would however not be exclusive, some individuals (n = 13) would have indeed occasionally consumed other resources such as freshwater fish or C4 cereals. Our results indicate that changes of diet during the life history are relatively limited. Besides, with regard to consumed food, this population is distinguished from other contemporary Roman populations for whom isotopic values are published. In the third place, we studied individual’s mobility patterns based on a rigorous approach to our data and on a comparison of the most comprehensive repositories as possible with taking into account the bias usually evaded (cultural facts, influence of climate and errors associated with conversion equations). Our results highlight that a minimum of 23% (n = 30) of the studied individuals are migrants. These, however, are not distinguished from Roman residents through their diet. We were able to show further that these migrants had complex and heterogeneous trajectories during their life within three distinct mobility patterns characterizing them. In terms of migrant’s rates, our population does not differ from other Roman populations for which the isotopic data are available. It differs however by its cosmopolitanism with origins for more diverse migrants: Europe, Africa, Arabia and Asia Minor [...]. / Tra il 2003 e il 2010, nella regione centrale chiamata X della catacomba dei Santi Pietro e Marcellino a Roma, è stato scoperto e parzialmente scavato un insieme di sepolture plurime inedite (I-III sec. D.C.) contenente diverse centinaia di individui, i quali sono stati inumati secondo le pratiche funerarie singolari in seguito ad un episodio di sovramortalità di natura probabilmente epidemica. Per comprendere la storia di vita (alimentazione e mobilità) di questi defunti e ridiscutere, sulla base di nuovi elementi, alcune ipotesi precedentemente formulate, abbiamo condotto, nel quadro di questo lavoro, un approccio archeo-biogeochimico multi-proxys (14C, δ13C, δ15N, δ18O e 87Sr/86Sr) e multi-tessuto (smalto, ossa, capelli) su un campione di 130 individui da sei stanze diverse. Abbiamo inizialmente verificato l'integrità biochimica e isotopica delle frazioni minerali (fasi carbonatiche) ed organiche (fasi collageniche e cheratiniche) dei campioni provenienti da indicatori classici misurati in routine (%Col, %C, %N, C/N, PCO2 e PCO2/Massa) e per spettroscopia FTIR (IRSF, CO3/PO4 e AmmideI/PO4) ed un approccio innovativo costituito da datazione 14C su coppie collagene-apatite per validare il segnale isotopico delle frazioni minerali. I nostri risultati mettono in evidenza delle differenze estreme di preservazione di tutte le fasi. La traiettoria diagenetica dei campioni non è però aleatoria, ma dipendente dalle condizioni ambientali e tafonomiche che differiscono tra camere piccole e grandi. Inoltre, abbiamo potuto dimostrare che nonostante delle forti ricristallizzazioni e degli scambi isotopici con l'ambiente sepolcrale, le fasi carbonatiche hanno un segnale isotopico biogenetico inalterato. Abbiamo in un secondo tempo ricostruito i regimi alimentari degli individui basandoci su riferimenti di confronto robusti e vari modelli interpretativi (mono-proxys versus multi-proxys, qualitativi versus quantitativi), i quali sono stati in alcuni casi, adattati alle esigenze del nostro studio. In generale, i nostri risultati mostrano che la maggior parte degli individui ha avuto accesso ad un regime alimentare tipo basato sulla triade Cereali C3/Carne C3/Pesci marini. Questo regime alimentare non è tuttavia esclusivo, avendo certi individui (n = 13) consumato casualmente altre categorie di risorse come il pesce dulciacquicolo o dei cereali C4. I nostri risultati indicano che i cambiamenti di alimentazione nel corso della vita sono relativamente limitati. Inoltre, questa popolazione si distingue da un piano strettamente alimentare rispetto alle altre popolazioni contemporanee romane per le quali dei valori isotopici sono pubblicati. Abbiamo in un terzo tempo studiato gli schemi di mobilità degli individui basandoci su un approccio rigoroso dei nostri dati e su riferimenti di confronto i più esaustivi possibile, e anche tenendo conto di punti di vista solitamente elusi (fatti culturali, influenza del clima e errori associati alle equazioni di conversione). I nostri risultati mettono in luce che a minima 23% (n = 30) degli individui studiati sono migranti. Questi ultimi, tuttavia, non si distinguono per la loro alimentazione dai residenti romani. Abbiamo potuto mostrare, inoltre, che questi migranti hanno avuto percorsi di vita complessi ed eterogenei e che tre schemi di mobilità distinti li caratterizzano. Nostra popolazione non si differenzia in termini di tasso di migranti da altre popolazioni romane per le quali sono disponibili dei dati isotopici. Essa si distingue tuttavia per il suo cosmopolitismo con delle origini per i migranti delle più diverse: Europa, Africa, Arabia e Asia Minore [...].

Les piles à combustibles à électrolyte solide de type SOFC permettent de transformer directement l’énergie de la réaction chimique de formation de l’eau à partir de l’hydrogène et de l’oxygène, en énergie électrique. De nos jours, les apatites de type silicates de terres rares présentent beaucoup d’intérêt comme électrolyte solide en raison de leurs propriétés de transport élevées avec une forte conductivité ionique et une faible énergie d'activation. Ils peuvent fonctionner de manière stable à une température intermédiaire sur une large plage de pression partielle d'oxygène en maintenant d'excellentes performances. Ils sont ainsi considérés comme de bons candidats pour les électrolytes de piles de type IT-SOFC. Parmi cette série de conducteurs, le type La-Si-O possède une conductivité plus élevée et leur performance serait modifiée par différents éléments dopants.L'objectif de cette thèse est d'étudier les effets des éléments de substitution / dopage ainsi que les méthodes de synthèse sur les propriétés structurales ainsi que sur la conductivité des apatites de type silicates de lanthane. Dans cette étude, nous utilisons une double approche: une approche de simulation et une approche expérimentale pour optimiser la pureté et les performances des matériaux d'électrolyte.Dans l'approche de simulation, le calcul basé sur la DFT (Théorie de la fonctionnelle de la densité) a été réalisée en vue d’étudier l'effet des positions de dopage: dopant Sr à La position de La et dopant Ge à la position de Si. Les résultats obtenus par le calcul concernant la conductivité ionique confirment ceux obtenus par l’expérience.Avec l’approche expérimentale, nous présentons la synthèse et la caractérisation de La10Si6O27 (LSO) dopé par Sr et élaboré par des procédés sol-gel. Les résultats montrent que la conductivité ionique est activé thermiquement et que les valeurs se situent entre 4,5 × 10-2 et 1 x 10-6 S·cm-1 à 873 K et dépend des conditions d’élaboration et de la composition de la poudre. / The Solid Oxide Fuel Cell (SOFC) defined by its ceramic and oxide electrolyte, is an electrochemical energy conversion device that produces electricity directly from the chemical reaction of fuel. Nowadays, apatite type rare earths silicates and germaniums attract many interests as the solid electrolyte due to the superior transport properties with high ionic conductivity and low activation energy. They can operate stably at intermediate temperature over a wide oxygen partial pressure range and maintain excellent performances, being considered as a candidate for IT-SOFC electrolytes. Among this series of conductors, the La-Si-O type has a higher conductivity and the performance would be modified by different doping elements.The objective of this thesis is to study the effects of element substitution/doping and synthesis methods on the structural and conductivity properties of apatite type lanthanum silicates. In this study, we use a double approach: a simulation approach and an experimental approach to optimize the electrolyte materials purity and performance.Using simulation approach, a first principle calculation based on DFT (Density Functional Theory) was carried out to investigate the effect on doping positions: Sr dopant at La position and Ge dopant at Si position. The calculation results give a connection to the ionic conductivity obtained by experiments.With experimental approach, we present the synthesis and characterization of Sr-doped La10Si6O27 (LSO) prepared through an optimized water-based sol-gel process. The results show that the ionic conductivity is thermally activated and values lies between 4.5×10-2 and 1×10-6 Scm-1 at 873 K as a function of the composition and powder preparation conditions.

On June 15, 1991, Mount Pinatubo, Philippines, ejected 20 million tonnes of sulfur dioxide into the atmosphere, significantly impacting global climate and stratospheric ozone. Recharging basaltic magma mixed into the 50 km³ dacitic magma reservoir 6 to 11 km beneath Mount Pinatubo, and triggered the 1991 eruption. The result of the magma mixing was a hybrid andesite with quenched basalt inclusions that erupted as a dome between June 7 and June 12. On June 15, approximately 5 km³ of anhydrite-bearing magma was erupted from the main phenocryst-rich, dacitic reservoir. This study will utilize this extraordinary framework of the 1991 Pinatubo eruption to investigate the systematics of sulfur uptake by apatite in order to further develop apatite as a monitor for magmatic sulfur. In the dacite and hybrid andesite, apatite occurs as individual phenocrysts (up to ~200 μm diameter) or included within anhydrite, hornblende, and plagioclase phenocrysts. In the basaltic magmatic inclusions, apatite is found as acicular microphenocrysts. Electron microprobe data collected on apatite yield low- (0.7 wt.% SO₃) apatites in all juvenile products, and show that two distinct populations of apatites exist: "silicic" apatites (hosted in dacite and andesite) and basalt apatites. Apatites crystallizing from silicic melt have predominantly low- to medium-sulfur contents, but high-sulfur apatites with as much as 1.2-1.7 wt.% SO₃ occur sporadically as inclusions in plagioclase, hornblende, Fe-Ti oxide, and anhydrite. These concentrations are much higher than what could be achieved through equilibrium crystal-melt partitioning at pre-eruption conditions (760±20°C, 220MPa, NNO+1.7, 77 ppm S in melt inclusions) and a partition coefficient of 13. Apatite in the basalt is always sulfur-rich with compositions forming a continuous array between 0.7 to 2.6 wt.% SO₃. The population of apatite that crystallized from silicic melt has elevated cerium, fluorine, and chlorine and lower magnesium concentrations (average dacite values in wt.%: 0.21 Ce₂O₃, 1.4 F, 1.1 Cl, & 0.14 MgO) relative to the population of apatite from the basalt (average basalt values in wt.%: 0.05 Ce₂O₃, 1.0 F, 0.78 Cl, & 0.22 MgO). LA-ICP-MS trace element data also show distinct apatite populations between silicic and basalt apatites. Silicic apatites have elevated REE concentrations (La avg. = 750 ppm), lower Sr (avg.= 594 ppm), and a pronounced negative Eu anomaly (avg. Eu/Eu* = 0.57) relative to basalt apatites (avg. values: 217 ppm La, 975 ppm Sr, and Eu/Eu* = 1.16). The correlation of EMP sulfur data and LA-ICP-MS trace element data show no difference between high-S and low-S silicic apatites. These compositional systematics rule out the possibility that sulfur-rich apatite from dacite are inherited from mafic magma. Sulfur element maps of apatites show no evidence of S-diffusion from anhydrite hosts. Areas of high-S concentrations show complicated patterns that suggest multiple periods of sulfur enrichment. High-S silicic apatites are likely the product of "fluid-enhanced crystallization" from early enrichment of a SO₂ rich fluid phase from the underplating basalt, which occurred prior to or at anhydrite saturation. This fluid phase is the only possible sufficient source of sulfur for generating high-S apatites in a cool, "wet", dacitic melt. The dynamics of apatite sulfur enrichment via "fluid-enhanced crystallization" is yet unclear and requires further experimental laboratory investigation.

No description available.

Ce travail de thèse porte sur l'étude d'un verre aluminoborosilicate de terre rare de composition molaire 61,81 SiO2 - 3,05 Al2O3 - 8,94 B2O3 - 14,41 Na2O - 6,33 CaO - 1,90 ZrO2 - 3,56 Nd2O3, destiné au confinement des déchets issus du retraitement de combustibles nucléaires usagés à haut taux de combustion. Au niveau structural, nous nous sommes intéressés principalement au rôle des ions modificateurs sur l'organisation du réseau vitreux par le biais de différents changements de composition : variation du rapport relatif Na/Ca et changement de la nature des ions alcalins et alcalino-terreux. Les études par spectroscopies RMN et Raman nous ont permis de préciser la distribution de ces différents types d'ions au sein du réseau vitreux et également d'apporter des informations sur les phénomènes de compétition entre les ions alcalins et alcalino-terreux vis à vis de la compensation de charge des entités [AlO4]- et [BO4]-. L'environnement du néodyme a pu être sondé par spectroscopies d'absorption optique et EXAFS ce qui a aboutit à une meilleure compréhension du mode d'insertion des ions Nd3+ au sein des zones silicatées du réseau vitreux. En ce qui concerne le comportement en cristallisation, nous nous sommes intéressés à l'influence de la composition du verre sur sa cristallisation et en particulier sur la formation d'une phase apatite de composition Ca2Nd8(SiO4)6O2. Ces travaux ont notamment souligné le rôle important des ions terres rares et alcalino-terreux sur la cristallisation de la phase apatite.

III Summary This thesis is focused on crystal chemistry and crystal structure of apatites from alkaline rock of the Bohemian Massif. Fifteen samples of volcanic rocks, mostly of the Cenozoic age was selected for the study. Sample No. 5 is of the Silurian age. Sample No. 15 originates from volcanic rock of the Cenozoic age from the Slovak Western Carpathians. This sample was chosen for this study due to its substantially different chemical composition. The contents of major and minor elements in apatites were measured on an electron microprobe, the contents of some minor and trace elements were determined by laser ablation inductively coupled plasma mass spectrometry. Selected samples were investigated by cathodoluminescence (CL) spectrometry. Crystal structure of studied apatites was characterized by X-ray diffraction and Raman spectroscopy. It was found that dominant anion at position X is fluorine. The OH content calculated on the basis of the fully occupied position X is significant in some samples. The amount of Cl is generally low. The exception is the sample No. 15 where Cl reached up to 0.6 apfu (Z = 2). Studied apatites contain many substitutions but they are generally of minor extent. Strontium, iron and REE at position M belong to the most common and most important substituents for calcium in...

[pt] A hidroxiapatita (Hap) é um mineral bastante estudado, devido à sua excelente biocompatibilidade e similaridade química com a porção mineral do osso humano. A hidroxiapatita estequiométrica Ca10(PO4)6(OH)2, com razão Ca/P igual a 1,67, pode ser de origem natural ou sintética. Os processos de fabricação são os mais diversos e a qualidade do produto dependente da natureza dos reagentes e dos parâmetros utilizados no processo, sendo importante, posteriormente, a sua caracterização estrutural e elementar. O presente trabalho tem como objetivo estudar a determinação da razão Ca/P em hidroxiapatita utilizando duas técnicas analíticas distintas: espectrometria de absorção atômica de alta resolução com fonte contínua (HR-CS AAS) e espectrometria de emissão óptica com plasma indutivamente acoplado (ICP OES). No caso da HR-CS AAS, os parâmetros instrumentais estudados foram vazão de acetileno, altura do queimador, taxa de aspiração e em seguida, número de pixels e tempo de integração. Já na técnica de ICP-OES, os parâmetros foram taxa de aspiração, potência da radiofrequência e vazão do gás de nebulização. Foi realizada uma otimização multivariada e as condições ótimas para cada parâmetro estudado foram determinadas pela função desejabilidade. O meio de leitura por HR-CS AAS para o cálcio foi uma solução HNO3 0,2 por cento v/v e KCl 1 por cento m/v e, para o fósforo, HNO3 5 por cento e KCl 0,1 por cento, já por ICP OES só foi empregado o HNO3 nas concentrações já especificadas A maior contribuição à incerteza do resultado final foi devido às soluções de calibração. Uma amostra de hidroxiapatita, produzida no Laboratório de Biomateriais do Centro Brasileiro de Pesquisas Físicas (CBPF) apresentou resultados de suas razões molares concordantes quando analisada pelas técnicas empregadas neste trabalho. / [en] Hydroxyapatite is a widely studied mineral due to its excellent biocompatibility and chemical similarity with the mineral portion of human bone. Stoichiometric hydroxyapatite Ca10(PO4)6(OH)2 with a Ca/P ratio of 1.67 can be natural or synthetic. Its manufacturing processes are diverse and the final product depends on the mineral type and the parameters used in the process, and subsequent structural and elemental characterizations are important. This study aims to determine hydroxyapatite Ca/P ratios by using two different analytical techniques: HR-CS AAS and ICP OES. In the case of HR-CS AAS the following instrumental parameters were studied: acetylene flow rate, burner height, rate of aspiration, pixels and integration time. In the ICP-OES technique, the parameters were rate of aspiration, radiofrequency power and nebulizer gas flow rate. We performed a multivariate optimization and optimal conditions for each studied parameter were determined by the function of desirability. The HR-CS AAS measurements for calcium were conducted in a medium containing HNO3 0.2 per cent v/v and KCl 1 per cent m/v and, for phosphorous, a medium containing HNO3 5 per cent and KCl 0.1 per cent was used. For the ICP OES measurements we used only HNO3 at the concentrations specified above. The major contribution to the uncertainty of the final results was from the calibration solutions. A hydroxiapatite sample, produced in the Biomaterial Laboratory at the Brazilian Center for Physical Research (CBPF), presented compatible molar ratio results among themselves when analyzed by the techniques utilized in the present study.

A temperatura de operação de células a combustível de óxido sólido (SOFCs) que utilizam zirconia estabilizada com itria (YSZ) como eletrólito é 1000 oC. Essa alta temperatura gera graves problemas relativos a materiais e vida util da célula. Por isso, condutores iônicos que possuem alta condutividade em temperaturas inferiores são pesquisados atualmente. Estudos mostraram que La10Si6O27 tipo apatita possui alta condutividade iônica de oxigenio, que é comparativamente maior que a de YSZ, a 500 oC, sendo, portanto, um potencial candidato como eletrólito para SOFC. O objetivo do presente trabalho é o desenvolvimento de técnicas de síntese de silicato de lantânio tipo apatita. Rotas inéditas de solgel modificada para sintetizar La9,33Si6O26 são propostas. Volumes estequiométricos de soluções de Na2SiO3 e LaCl3 foram misturados para a formação de gel de Si. Em seguida este gel foi calcinado a 900 °C, lavado, filtrado e tratado novamente a 900 °C. Em outra rota, volumes estequiométricos de soluções de Si (Na2SiO3 ou TEOS) e de La (LaCl3) foram utilizados para obtenção de gel de Si. Em seguida, hidróxido de La foi precipitado pela adição de uma base (NaOH ou NH4OH) ao gel. O material resultante foi calcinado a 900 °C, lavado, filtrado e tratado novamente a 900 °C. Pós de aglomerados fracos e alta sinterabilidade foram obtidos. DRX dos pós mostrou a estrutura de apatita monofásica a 900 oC. Morfologia de ceramica densa foi observada em imagens de MEV da superfície das pastilhas sinterizadas a 1200,1300 e 1400 oC por 4 h. Estas temperaturas e tempo de sinterização são significativas, pois no método convencional temperaturas superiores a 1700oC e tempos muito maiores são necessários para obtenção de tais cerâmicas. Densidades relativas superiores a 90% foram obtidas através dos métodos propostos. Uma conclusão importante é que TEOS, o reagente usual de alto custo, pode ser substituído por Na2SiO3, de preço muito mais baixo, para obter La9,33Si6O26 tipo apatita. / Solid oxide fuel cell (SOFCs) operating temperature that uses yttria stabilized zirconia (YSZ) as the electrolyte is 1000ºC. This high temperature causes serious problems concerning cell life and materials. Therefore, the ionic conductors which have high conductivity at lower temperature are currently researched. Studies have shown that the composition of La10Si6O27 apatite type has high oxygen ionic conductivity, which is comparably higher than that of YSZ, at 500 oC, it is therefore a potential candidate as for SOFC electrolyte. The objective of the present work is the development of lanthanum silicate with apatite type synthesis techniques. Novel modified solgel routes to synthesize La9.33Si6O26 are proposed. Stoichiometric volumes of Na2SiO3 and LaCl3 solutions were mixed for the formation of Si gel. This gel was calcined at 900 °C, washed, filtered and again thermally treated at 900 °C. In the other route, stoichiometric volumes of Si (Na2SiO3 or TEOS) and La (LaCl3) solutions were used for obtaining Si gel. Then, La hydroxide was precipitated by adding of a base (NaOH or NH4OH) to gel. Then the material was calcined at 900 °C, washed, filtered and again treated at 900 °C. Highly sinterable weakly agglomerated powders have been obtained. XRD patterns of the powders showed the single-phase apatite structure at 900 oC. Dense ceramic morphology was observed from the SEM images of surface of the pellets sintered at 1200, 1300 and 1400oC for 4h. This low temperature sintering and time of sintering are significant because the conventional method requires superior temperatures of 1700 oC to obtain the same dense ceramics. High relative densities higher than 90% was obtained via proposed methods. An Important conclusion is the TEOS, the usual high cost reagent, may be substituted by a cheap price Na2SiO3, to obtain apatite type La9.33Si6O26.

Cerâmicas de silicato de lantânio tipo apatita têm sido estudadas devido ao grande interesse tecnológico para aplicação como eletrólito em células a combustível de óxido sólido de temperatura intermediária (IT-SOFC: Intermediate Temperature Solid Oxide Fuel Cell). A condutividade iônica dessas cerâmicas em temperaturas intermediárias (600-800°C) é maior do que a da YSZ (Ytria Stabilized Zirconia) utilizada como eletrólito em SOFCs de alta temperatura (800-1000°C). Neste trabalho, silicato de lantânio tipo apatita foi sintetizado pelo método sol-gel seguido de precipitação, a partir de Na2SiO3 como fonte de sílica. No método proposto, estudou-se rotas de síntese em meio ácido e básico para a formação do gel de sílica, seguida de precipitação. A fase cristalina de silicato de lantânio tipo apatita foi obtida pela calcinação de pós sintetizados a 900°C. Esta temperatura é muito inferior às praticadas em outros métodos convencionais de síntese. As análises por difração de raios X (DRX) mostraram silicato de lantânio tipo apatita como fase principal do material sintetizado na rota de síntese em pH ácido. No entanto, uma fase secundária indesejável, La2Si2O7, foi identificada quando o pó cerâmico foi calcinado a 1200°C. Por outro lado, pela rota básica, fase única de silicato de lantânio tipo apatita foi obtida após tratamento térmico dos precursores a 900 e 1200°C. Pastilha cerâmica obtida a partir dos pós obtidos e sinterizados a 1400°C por 4h, apresentaram fase cristalina pura de silicato de lantânio tipo apatita. Microscopia eletrônica de varredura (MEV) foi utilizada para observar a morfologia dos pós e microestrutura das pastilhas sinterizadas. Pós cerâmicos finos com tamanho de partículas submicrométricas e microestrutura típica de apatita foram alcançadas pelo método proposto. / Lanthanum silicate apatite-type ceramics have been studied because of the great technological interest for IT-SOFC applications as electrolyte (Intermediate Temperature Solid Oxide Fuel Cell). Ionic conductivity of those ceramics at intermediate temperatures (600-800°C) is higher than that of YSZ (Ytria Stabilized Zirconia) electrolyte used at high-temperatures (800-1000 °C) SOFCs. In this work, lanthanum silicate apatite-type was synthesized by sol-gel method followed by precipitation from Na2SiO3 as a source of silica. In the proposed method, synthesis routes in acid and basic medium to the formation of silica gel, followed by precipitation were studied. Apatite crystalline phase of lanthanum silicate ceramic was obtained by calcining the powders at 900°C. This temperature is much lower than those other conventional methods of synthesis. Analysis by x-ray diffraction (XRD) showed the lanthanum silicate apatite-type phase as the main phase of the synthesized material at the pH acid synthesis route. However, undesirable secondary phase, La2Si2O7, was recognized when the powder was calcined at 1200°C. On the other hand, by the basic route, single apatite-type phase powder was obtained after thermal treatment of the precursors at 900 and 1200°C. Ceramic pellet obtained from those powders sintered at 1400°C for 4h, presented pure apatite crystalline phase of lanthanum silicate. Scanning electron microscopy (SEM) was used to observe morphology of powders and microstructure of sintered pellets. Sub micrometric size powders and apatite typical microstructure ceramic were reached by the suggested method.

O presente estudo refere-se à caracterização tecnológica de tipos de minério de fosfato residual do complexo alcalino-carbonatítico de Salitre (MG), em área de interesse da Fosfertil. O procedimento experimental consistiu de moagem das amostras abaixo de 0,21 mm, análise granulométrica por peneiramento a úmido e separações minerais (líquido denso e Frantz). A composição mineralógica bem como a liberação da apatita e suas formas de associação com a ganga foram determinadas através de sistema de análise de imagens por feixe de elétrons (Mineral Liberation Analyser), com apoio de análises por DRX e MEV/EDS. As composições químicas dos produtos gerados foram determinadas por FRX. Seis amostras com graus distintos de intemperismo foram estudadas: apatitito (APAT), foscorito intemperizado (FIT), foscorito silicificado (FST), zona de mistura (ZMT), piroxenito intemperizado (PIT) e piroxenito (PXT). Os teores de P2O5 variam de 9 a 25% e a composição mineralógica é similar para todas as amostras, variando apenas as proporções relativas entre as espécies minerais. As amostras mais intemperizadas (APAT e FIT) são basicamente constituídas por apatita e magnetita; a amostra PIT apresenta também conteúdos elevados de filossilicatos e quartzo. Já as amostras menos intemperizadas (PXT, FST e ZMT) contêm maiores proporções de filossilicatos e diopsídio, principalmente a amostra PXT. A parcela de fósforo não apatítico varia de 10 a 20% nas amostras PIT e FIT e de 1 a 6% nas demais, sendo mais expressiva nos finos (<0,020 mm). Para cominuição abaixo de 0,21 mm, o conteúdo de finos varia de 20 a 34% e a parcela de fósforo associada a estes é de 13 e 16% nas amostras APAT, FIT e PIT e de 19 a 21% nas demais. Acima de 0,020 mm, a apatita representa de 96 a 98% do P2O5 (89% na amostra PIT); a liberação da apatita é superior a 90% nas amostras APAT, FIT e PIT, variando de 85 a 89% nas demais. Os resultados obtidos sugerem que a composição mineralógica e suas formas de associação não devem opor maiores dificuldades à concentração da apatita por flotação, podendo-se, em princípio, restringir a variabilidade do minério estudado a três tipos principais para fins de processamento mineral. / The present study refers to the technological characterization of residual phosphate ore types from Salitre alkaline-carbonatitic complex (MG), in Fosfertil area. The procedure comprised grinding the samples bellow 0.21 mm, size analysis by wet screening and mineral separations (heavy liquid and Frantz). Mineralogical composition as well as apatite liberation and its associations to gangue minerals were determined by SEM-based image analysis (Mineral Liberation Analyser) and supported by XRD and SEM/EDS. Chemical compositions of all generated products were determined by XRF. Six samples with different weathering grades were studied: apatitite (APT), weathered foskorite (FIT), silicified foskorite (FST), mixture zone (ZMT), weathered piroxenite (PIT) and piroxenite (PXT). The P2O5 grades vary from 9 to 25% and mineralogical composition is similar to all samples, varying only the relative proportions among mineral species. The deeply weathered samples (APAT and FIT) are basically constituted by apatite and magnetite; PIT shows also high content of phyllosilicates and quartz. On the other hand, the less weathered samples (FST, ZMT and PXT) have major amounts of phyllosilicates and diopside, especially PXT. The non-apatitic phosphor varies from 10 to 20% in samples PIT and FIT and from 1 to 6% in the others; these contents are mostly expressive in fines (<0.020 mm). The fine content, considering comminution under 0.21 mm, varies between 20 and 34% w/w, while the related distribution of apatitic phosphor corresponds from 13 to 16% in the samples APAT, FIT and PIT and from 19 to 21% in the others. Above 0,020 mm, apatite represents 96 to 98% of total phosphor (89% in sample PIT); its liberation grade overcomes 90% in APAT, FIT and PIT, varying from 85 to 89% in the other samples. The results suggest that mineralogical composition and its associations should not oppose major difficulties to apatite concentration by froth flotation and that might be possible to restrict the ore variability to three main oretypes for mineral processing.