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Pegmatitska provincija Borborema (BPP) nalazi se u E – SE dijelu pojasa borâ Seridó i tektonskog područja Rio Grande do Norte, u saveznim državama Paraíba i Rio Grande do Norte. Lokalitet na kojem su uzorkovane nodule granata, Serrote Redondo, nalazi se 9 km južno od Pedra Lavrade. Cilj ovog istraživanja jest kristalografska karakterizacija granata koji se nalazi unutar polimineralne nodule. Uz pomoć metoda fazne i elementne analize (optička istraživanja u prolaznoj svjetlosti, XRPD, FTIR, SEM-EDS, klasična kemijska analiza) analizirani su kristali granata i mineralna asocijacija samih nodulâ. Nakon sprovedenih analiza, može se zaključiti kako se radi o almandinu, koji se pojavljuje u vidu izomorfnih kristala centimetarskih dimenzija, a koji se nalazi unutar polimineralnog matriksa, uglavnom sastavljenog od feldspata, kvarca, sillimanita, opâkih minerala, te akcesornih mineralnih faza (npr. cirkon, monacit). The Borborema Pegmatite Province (BPP) is located in the E – SE part of the Borâ Seridó belt and the Rio Grande do Norte tectonic area, in the federal states of Paraíba and Rio Grande do Norte. The locality where the garnet nodules were sampled, Serrote Redondo, is located 9 km south of Pedro Lavrada. The main goal of this research is the crystallographic characterization of the garnet found inside the polymineral nodule. With the help of phase and elemental analysis methods (transmitted light optical research, XRPD, FTIR, SEM-EDS, classical chemical analysis), garnet crystals and the mineral association of the nodules themselves were analyzed. After conducting the analyses, it can be concluded that the garnet mineral in question is almandine, which appears in the form of isomorphous crystals of centimeter dimensions, and which is located within a polymineral matrix, mainly composed of feldspar, quartz, sillimanite, opaque minerals, and accessory mineral phases (e.g. zircon, monazite).

Mixed anions compounds may allow to reach structures and properties inaccessible in the case of single anion phases, which provide great opportunities for exploratory research of functional mixed anions compounds. One major interest of mixing anions in a phase is the band gap engineering by controlling the contribution of anionic orbitals at the top of the valence band, hence controlling the electronic structure and the properties. In addition, heteroleptic environments around a cation (directly surrounded by at least two types of anions) makes it possible to accentuate the acentric character of a structural entity, and therefore the polarity in the case of a polar arrangement comparing to a mono-anionic analogue. These two aspects combined, i.e. band gap engineering and local acentric character both reached with multiple anions, are powerful to control and exacerbate various properties. With the aim to reach such environments in innovative mixed anion phases and study their physical and chemical properties, several series of potential materials were formulated based on interesting mixed anion building blocks and their synthesis attempted. In this work, a wide variety of new systems are presented, including some unusual environments and properties: Non-linear optical properties, magnetic properties and photoelectric properties . Among these compounds, a large series of new compounds, including Ba5(VO2S2)2(S2)2, characterized by heteroleptic thiovanadates (VO2S2, VO3S, VOS3) and the presence of dichalcogenide pairs are described. From those building blocks, our strategy to reach polar phases was successful with one of those compounds showing interesting non-linear optical properties (SHG). Also, a series of versatile halide-thiovanadates phases (halide= F, Cl and I) could also be developed and proves the appearance of a photoelectric current under visible light. In addition, their calculated bands alignment with respect to H2 and O2 evolution reactions makes them potential candidates for photocatalysis of water-splitting under visible light. On another hand, the first Fresnoite oxysulfide (polar) with SHG properties is also presented. Finally, magnetic phases were also developed like the non-centrosymmetric Ba10Fe7.75Zn5.25S18Si3O12, with (Fe/Zn)3O mixed anion tetrahedra involved in an original large magnetic cluster as elementary block. Those series of compounds are discussed with combination of DFT calculations in order to deliver a comprehension of their structure-properties relationships to help further design functional mixed anion materials.; Les composés à anions mixtes peuvent permettre d'atteindre des structures et des propriétés inaccessibles dans le cas de phases mono-anionique, ce qui offre de nombreuses opportunités pour la recherche exploratoire de composés à anions mixtes fonctionnels. Un intérêt majeur de la présence d’anions multiples au sein d’une phase est l'ingénierie du band gap via les contributions des orbitales anioniques en haut de la bande de valence, permettant ainsi le contrôle de la structure électronique et des propriétés. De plus, les environnement hétéroleptiques autour d'un cation (entouré d'au moins deux types d'anions) permettent d'accentuer le caractère acentrique d'une entité structurale, et donc la polarité dans le cas d'un arrangement polaire par rapport à un analogue mono-anionique. Ces deux aspects combinés, c'est-à-dire l'ingénierie du band gap et le caractère acentrique local tous deux modulables avec plusieurs anions, sont puissants pour contrôler et exacerber diverses propriétés. Dans le but d'atteindre de tels environnements dans des phases innovantes à anions mixtes et d'étudier leurs propriétés physiques et chimiques, plusieurs séries de composés ont été formulées sur la base d’unités structurales à anions mixtes intéressantes et leurs synthèses ont été tentées. Dans ce travail, une grande variété de nouveaux systèmes sont présentés, y compris certains environnements peu répandus et propriétés remarquables : propriétés d’optique non linéaire, propriétés magnétiques et propriétés photoélectriques. Parmi ces composés, une grande série de nouveaux composés, dont Ba5(VO2S2)2(S2)2, caractérisés par des thiovanadates hétéroleptiques (VO2S2, VO3S, VOS3) et la présence de paires dichalcogénures sont décrits. À partir de ces éléments constitutifs, notre stratégie pour atteindre les phases polaires a été couronnée de succès avec l'un de ces composés présentant des propriétés d’optique non linéaires (SHG) intéressantes. Aussi, une série de phases polyvalentes halogénure-thiovanadates (halogénure = F, Cl et I) a également pu être développée et montre l'apparition d'un courant photoélectrique sous lumière visible. De plus, l’alignement des bandes calculées par rapport aux réactions d'évolution de H2 et O2 en fait des candidats potentiels pour la photocatalyse de l'eau sous lumière visible. D'autre part, le premier oxysulfure de type Fresnoite (polaire) aux propriétés SHG est également présenté. Enfin, des phases magnétiques ont également été développées comme le composé Ba10Fe7.75Zn5.25S18Si3O12 non centrosymétrique, avec des tétraèdres à anions mixtes (Fe/Zn)3O impliqués dans un cluster magnétique original qui forme l’unité structurale élémentaire. Ces séries de composés sont discutées en s’appuyant également sur des calculs DFT afin de fournir une compréhension de leurs relations structure-propriétés pour aider à concevoir davantage de matériaux à anions mixtes fonctionnels.

Väitekirja elektrooniline versioon ei sisalda publikatsioone, Käesoleval ajal on suur vajadus funktsionaalsete materjalide järele, mis võiksid olla aluseks uute energiaefektiivsete seadmete ja mehhanismide arendamisel, millel on lai rakendusvaldkond ja võime funktsioneerida erinevates maa- ja kosmosetingimustes. Nagu esimesed tulemused on näidanud, on haruldaste muldmetallide oksühüdriididel mitmeid kasulikke funktsionaalseid omadusi, mida saab otseselt kasutada kaasaegsetes tehnoloogilistes lahendustes, eelkõige kõrgefektiivsete optiliste ja elektromehaaniliste seadmete arendamisel. Haruldaste muldmetallide oksühüdriidide keemiline projekteerimine algas rohkem kui 10 aastat tagasi, kui avastati, et hapniku lisamine hüdriidi struktuuri mitte ainult ei korralda ümber stöhhiomeetriat tänu vesiniku ja hapniku positsioonide paindlikule stabiliseerimisele kristallvõrega, vaid laiendab ka oluliselt modifitseeritud metallihüdriidide süsteemi omaduste kompleksi. See on avanud mitmesuguseid võimalusi parandada paljusid metallhüdriidide põhiomadusi ja suurendada nende funktsionaalsust, võimaldades seega teadlastel paindlikult modifitseerida ja muuta nende optilisi, mehaanilisi ja elektroonilisi omadusi. Teaduslikust ja tehnilisest seisukohast on kõige olulisem probleem välja selgitada, millist funktsionaalset rolli mängib hapniku keemiline lisamine tahkete oksühüdriidide omadustes. Seega oli käesoleva doktoritöö peamine eesmärk laiendada oluliselt meie teadmisi hapniku käitumisest haruldaste muldmetallide hüdriidides. Kasutades kaasaegseid matemaatika, teoreetilise füüsika ja kristallokeemia meetodeid ning mahukaid numbrilisi arvutusi superarvutis, uurisime haruldaste muldmetallide oksühüdriidide süsteemide kõige tõenäolisemaid struktuuri- ja koostise konfiguratsioone. See võimaldas meil ennustada suure hulga erinevate kristallstruktuuride ja hapniku/vesiniku vahekordadega ühendite teket ning konstrueerida ternaarne faasidiagramm Y- H-O muutujate puhul. Oleme kirjeldanud hapniku võtmerolli uute materjalide moodustamisel, mis mõjutab kristalliseerumist stabiilsesse oksühüdriidstruktuuri. Kõigist kolmekomponentsetest oksühüdriididest leidsime, et mõned oksühüdriidid on võimalik stabiliseerida polaarsetes mittetsentrosümmeetrilistes faasides, millel on silmapaistvad elastsed, piesoelektrilised ja elektromehaanilised omadused. Üks neist faasidest kuulub spetsiifilisele tetragonaalsele struktuurile, mille võrestiku konfiguratsioonil on unikaalne kiraalstruktuuriline ülesehitus, mis hõlmab kõiki elementaarraku katioone ja anioone. Arvutatud elektrooniliste ja optiliste omaduste põhjal pakkusime välja ka kaks erinevat optiliste katete prototüüpi, milles oksühüdriidi õhukesed kiled mängivad võtmerolli: i) madala emissiooniga katte mudel ja ii) valgust absorbeeriva mittepeegeldava katte mudel. Meie uurimistöö tulemused on oluliselt täiendanud haruldaste muldmetallide oksühüdriidide materjaliomadusi käsitlevat teadmistebaasi. Nad on tuvastanud nende materjalide elektrooniliste, elastsete, elektriliste ja optiliste omaduste mikroskoopilise olemuse detailid. See võimaldas meil mõista, kuidas nende omadused ja funktsionaalsed karakteristikud võivad olla tingitud erinevatest keemilistest ja füüsikalistest teguritest. Lisaks sellele oleme pakkunud välja võimalikud stsenaariumid perspektiivsete funktsionaalsete omadustega oksühüdriidmaterjalide prognoosimiseks ja projekteerimiseks, mida saab seejärel kasutada kaasaegsete optiliste ja elektromehaaniliste seadmete arendamisel., There is currently a high demand for functional materials that can serve as the basis for the development of new energy-efficient devices and mechanisms with a wide range of applications, capable of operating under various Earth and space conditions. As the first results have shown, rare-earth metal oxyhydrides offer a number of useful functionalities that can be directly utilized in modern technological applications, especially in the design of high-performance optical and electromechanical devices. Chemical engineering of rare-earth metal oxyhydrides has begun more than 10 years ago when it was discovered that the addition of oxygen into the hydride structure not only rearranges the stoichiometry due to the flexible stabilization of hydrogen and oxygen positions in the crystal lattice, but also greatly expands the set of characteristics of the modified metal-hydride system. This has opened up great opportunities to improve a number of key properties of metal hydrides and enhance their functionality, thus enabling researchers to flexibly modify and improve their optical, mechanical, and electronic properties. From a scientific and technological point of view, understanding what functional role the chemical addition of oxygen plays in the properties of solid oxyhydrides is the most important problem. Thus, the main goal of the present PhD thesis was to significantly extend our knowledge about the behavior of oxygen in rare-earth metal hydrides. Using modern methods of mathematics, theoretical physics and crystal chemistry, as well as extensive numerical calculations on a supercomputer, we investigated the most probable structural and compositional configurations in rare-earth metal oxyhydride systems. This allowed us to predict a large number of compounds with different crystal structures and oxygen/hydrogen ratios and construct a ternary phase diagram for Y-H-O variables. We have characterized the key role of oxygen in the formation of new materials, which guides crystallization into a stable oxyhydride structure. Among all ternary oxyhydride compositions, we found that certain oxyhydrides can be stabilized in polar noncentrosymmetric phases that have outstanding elastic, piezoelectric, and electromechanical characteristics. One of these phases corresponds to a special tetragonal structure whose lattice configuration is characterized by a unique chiral structural organization encompassing all cations and anions in the unit cell. Based on the calculated electronic and optical properties, we also proposed two different prototypes of optical coatings in which oxyhydride thin films play a key role: (i) a low-emissivity coating model and (ii) a light-absorbing non-reflective coating model. The results of our research have significantly enriched the knowledge base on the material properties of rare-earth metal oxyhydrides. They revealed details of the microscopic nature of the electronic, elastic, electrical, and optical properties of these materials. This allowed us to understand how their properties and functional characteristics could be driven by various chemical and physical factors. In addition, we proposed possible scenarios for the prediction and design of oxyhydride materials with promising functions, which can be further used in the development of modern optical and electromechanical devices., https://www.ester.ee/record=b5461494

Since conventional anti-slip enamels show some disadvantages, directly related to the surface roughness which prevents the adequate surface cleaning of tile, an anti-slip enamel exhibiting glass-ceramic nature has been designed, characterized by being stain-resistant and presenting a smooth texture and touch soft. To do this, new matte frits and raw materials with similar nature have been used, refractory enough to be suitable in enamel compositions for porcelain stoneware. The glass-ceramic glaze thus prepared was characterized by various instrumental techniques (X-ray fluorescence [XRF], scanning electron microscopy [SEM], X-ray diffraction [XRD], mechanical profilometry and microhardness measurements), in order to check the nature of crystallized phases, their morphology, surface roughness and microhardness of the finished tile. In addition, the quality of the glazed piece has been evaluated by the regulations of chemical resistance, stain-resistance and slipperiness. The enamel obtained has devitrified in crystals of silicoaluminates of calcium and barium and complies with standards of anti-slip and stain-resistence, as it has a surface roughness similar to a non-slip enamel. Dada la problemática que presentan los esmaltes antideslizantes convencionales, los cuales poseen una rugosidad superficial que dificulta la limpieza de la superficie de la pieza, se ha diseñado un esmalte antideslizante de naturaleza vitrocerámica que es resistente a las manchas y presenta una textura lisa, de tacto suave. Para ello, se han utilizado nuevas fritas de naturaleza mate y materias primas de composiciones similares, suficientemente refractarias para ser adecuadas para esmaltar piezas de gres porcelánico. El esmalte vitrocerámico así obtenido se ha caracterizado a través de varias técnicas instrumentales (fluorescencia de rayos X [FRX], microscopia electrónica de barrido [MEB], difracción de rayos X [DRX], perfilometría mecánica y medidas de microdureza) con el fin de comprobar la naturaleza de las fases cristalizadas, su morfología, la rugosidad superficial y la microdureza de la pieza acabada. Además, se ha valorado la calidad de la pieza esmaltada mediante las normativas de resistencia química, resistencia a las manchas y resistencia a la resbaladicidad. El esmalte obtenido ha desvitrificado en cristales de silicoaluminatos de calcio y bario, cumple la normativa de antideslizamiento y es resistente a las manchas, ya que presenta una rugosidad superficial similar a un esmalte no antideslizante. Los autores agradecen a la empresa Colores Cerámicos S.A. de Onda (Castellón) las facilidades ofrecidas para la realización del presente trabajo.

The need of a concerted multi-disciplinary approach in the investigation of intermetallic systems and the role of thermochemistry are underlined. The activity carried out in the Author?s laboratory in the alloy thermodynamics is summarized. The different instruments (calorimeters) built in laboratory are briefly presented and their performance discussed. The results obtained in the measurement of the enthalpy of formation mainly of several rare earth alloys are described. The characteristics of the Eu and Yb thermochemistry and crystallochemistry are finally underlined.

This paper presents results on the composition of Portland clinkers produced with non-conventional raw-materials and fuels, focusing on the distribution of selected trace elements. Clinkers produced with three different fuel compositions were sampled in an industrial plant, where all other parameters were kept unchanged. The fuels have chemical fingerprints, which are sulfur for petroleum coke and zinc for TDF (tire-derived fuel). Presence of carbonatite in the raw materials is indicated by high amounts of strontium and phosphorous. Electron microprobe data was used to determine occupation of structural site of both C3S and C2S, and the distribution of trace elements among clinker phases. Phosphorous occurs in similar proportions in C3S and C2S; while considering its modal abundance, C3S is its main reservoir in the clinker. Sulfur is preferentially partitioned toward C2S compared to C3S. Strontium substitutes for Ca2+ mainly in C2S and in non-silicatic phases, compared to C3S. Este artigo apresenta dados composicionais de amostras de clínquer Portland produzido com matérias-primas e combustíveis não convencionais, em especial no que diz respeito à distribuição de elementos menores e traços. Foram amostrados clínqueres produzidos com três misturas diferentes de combustíveis, enquanto os demais parâmetros foram mantidos constantes. Os combustíveis apresentam características químicas típicas, como o teor elevado de enxofre no coque de petróleo e o alto teor de zinco no combustível derivado de pneus. O uso de carbonatito como matéria-prima se reflete nos teores elevados de estrôncio e fósforo. Dados de microssonda eletrônica foram usados para determinar a ocupação de sítios estruturais de C3S e C2S, e para modelar a distribuição de elementos traços entre as fases do clínquer. O fósforo ocorre em proporções similares em C3S e C2S; se considerarmos sua abundância modal, o C3S é o principal reservatório de fósforo no clínquer. O enxofre é preferencialmente concentrado em C2S em comparação com C3S. O estrôncio substitui Ca2+ principalmente em C2S e em fases não-silicáticas, em comparação com C3S.

A presente dissertação apresenta um estudo sobre a fossildiagênese da Supersequencia Santa Maria. Esta unidade contém uma grande variedade de vertebrados fósseis, que são conhecidos deste o início do século XX. Muitas vezes a preservação destes fósseis é excelente, mas alguns não seguem esse padrão. Algumas vezes, o processo de crescimento dos minerais permineralizantes pode destruir a forma original dos ossos, o que impede, às vezes, a sua identificação taxonômica precisa. Este trabalho tem como objetivo principal estudar os diferentes tipos de fossilização que ocorrem nos pacotes fossilíferos da Supersequência Santa Maria (Sequências Santa Maria I e II). Para isso, foram realizadas análises petrográficas por microscopia óptica, difração de raios X, refinamento cristalino e por espectroscopia no infravermelho. Em alguns ossos, foram coletadas amostras (para análises geoquímicas) em distintas porções do osso (mais externas e mais internas). Os resultados obtidos possibilitaram estudar as modificações cristaloquímicas e diagenéticas da apatita que compõe os ossos fósseis e compreender a evolução dos processos de fossilização. Através das análises petrográficas, foi possível identificar todas as fases minerais envolvidas nestes processos e estudar as transformações da hidroxiapatita ao longo da diagenênese. As análises possibilitaram identificar calcita, hematita e calcedônia como minerais precipitados durante a fossilização e fluorapatita e carbonato fluorapatita como as variedades de apatita que ocorrem nos ossos. Também foram observadas diferenças nas microfeições de calcita em ossos bem preservados (cristais grandes preenchendo completamente as cavidades internas) e mal preservados (calcita micro espática típica de calcretes freáticos). Com base nos resultados, foram identificados dois padrões, sendo um para Sequencia Santa Maria I e base da Sequencia Santa Maria II e outro para o topo da Sequencia Santa Maria II. No primeiro caso, onde a rocha fossilífera é um pelito depositado em planície de inundação, existem duas variantes: 1) após o soterramento final, o osso não ficar na zona de oscilação de nível freático, acarretando um uma boa preservação e 2) o osso ficar na zona de oscilação de nível freático, recebendo maior aporte de íons e tendo uma probabilidade maior de sofrer alteração volumétrica. Estas duas possibilidades podem sobrepor-se. Já no topo na Sequencia Santa Maria II, a rocha fossilífera é um arenito fino e a preservação se dá pela percolação de íons fora da zona de oscilação do nível freático, implicando em uma boa preservação. O refinamento cristalino mostrou que, durante o processo de fossilização, a apatita sofre mudança nos parâmetros cristalográficos, indicando uma mudança mineralógica causada principalmente pela substituição dos ânions na estrutura cristalina, especialmente incluindo o flúor e o carbonato, íons muito comuns nas águas superficiais. As análises por espectroscopia no infravermelho permitiram constatar a entrada de carbonato e a diminuição de fosfato nas porções mais centrais do osso, que são as mais alteradas. Com isso, se pode concluir que as partes mais centrais dos ossos servem de conduto principal para os fluidos diagenéticos e que a alteração da hidroxiapatita para carbonato apatita ocorre de dentro para fora. The present master degree thesis presents a study about Santa Maria Supersequence fossildiagenesis. This unit contains a great variety of vertebrate fossils known since the early XX century. In many cases, the fossils are in excellent preservational state, although some of them do not follow this pattern. The process of expansive growth of the permineralizing minerals destroys the original shape of the fossils, which sometimes does not allow an accurate taxonomic identification. This work has as main objective to study the different fossilization patterns that occurs in Santa Maria Sequences I and II. For that, petrographic analyzes were performed by optical microscopy, X-ray diffraction, refinement and crystal infrared spectroscopy. In some bones were collected samples (for geochemical analysis) in different portions of the bone (from bone marrow to the edges). The results made possible to study the crystallochemical and diagenetic modifications of bone apatite in places with distinct preservational states, and understand the evolution of the fossilization processes. Through petrographic analyses were possible to identificate all mineral phases involved in fossilization process and to study hydroxylapatite transformations through fossildiagenetic process. Were identified calcite, hematite and chalcedony as precipited minerals during fossilization besides fluorapatite and carbonate fluorapatite as varieties of bone apatite after fossildiagenesis. Also were observed differences in calcite microfeatures between well preserved bones (big crystals filling all bone cavities) and badly preserved (microspar calcite, typical of phreatic precipitation). Based in these results were recognized two patterns, being one for Santa Maria Sequence I and Santa Maria Sequence II base and another to Santa Maria Sequencie II top. In the first case, the fossiliferous rock is a floodplain mudstone and there are two variables: 1) after the final burial bone stay out of phreatic level, favoring a good preservation and 2) bone stay in phreatic oscillation zone resulting in a bad preservation. These two possibilities may overlap. For Santa Maria Sequence II top the fossiliferous rock is a deltaic massive sandstone and the preservation occurs by ion percolation outside the phreatic oscillation zone, resulting in a good preservation. The crystalline refinement showed that during the fossilization processes bone apatite suffers changes in crystallographic parameters, indicating a mineralogical change due to anion substitution inside crystalline structure, especially floride and carbonate found in any sedimentary environment. Infrared spectroscopy made possible to observe the carbonate entry and the phosphate in the bone marrow. Due this, were concluded that the bone marrow serve as the primary conduit for the diagenetic fluids, and the change of hydroxylapatite for carbonate fluorapatite and fluorapatite occurs from the inside to outside.

International audience; Light harvesting chalcogenide materials have strong potential applications for photovoltaic due, in part, to the ability of their structures to accommodate shift from the ideal stoichiometry. This study is devoted to the chemical and structural investigations of two specific series of materials, Cu(In, Ga)Se2 (CIGSe) and Cu2ZnSnS4 (CZTS). Both of them receive currently a strong incentive in the domain of thin film solar cells. On the basis of accurate chemical analyses, conventional powder and single-crystal X-ray diffraction, resonant X-ray scattering with synchrotron radiation the capacity of the chalcopyrite and kesterite structures of CIGSe and CZTS to accommodate deviations from the stoichiometry is discussed. Formally, the former is found to be more flexible than the latter even if this one can self adapt to copper-poor and copper-rich compositions without any structural change except in terms of the cation distributions.

The aims of this study were to compare the crystal chemical properties of some commercial mineral trioxide aggregate (MTA) and Portland cements (PC) and to propose a new white MTA product.The samples (four MTA and two PC types) were analyzed by 1) optical microscopy; 2) laser granulometry; 3) X-ray diffraction and fluorescence; 4) scanning electron microscopy (SEM) and electron probe microanalysis (EPM) (wavelength-dispersive).MTA and PC specimens yielded similar characteristics in their clinker component. The MTA-Angelus specimens displayed a composition overlapping the classical clinker composition (wt%) i.e. 25 silica, nine alumina and 66 lime. However, the bismite, present in large amounts (~15-19 wt%) in all MTA products, contained considerable and diffused heavy (toxic) metals as Pb and Mo, other than Bi. In the MTA clinkers the formation of Portlandite, at water-clinker interface, is favored by the smaller grain size of the MTA particles. However, this may also favor the diffusion of the toxic elements linked to Bi.In terms of bulk physico-chemical properties, the MTA products can be easily substituted by a fine-grained Portland clinker by adding a non-toxic radio-opaque component, for example, Ba-carbonate.

Resume L'etude geochimique des micas de pegmatites de l'etat de Minas Gerais au Bresil a ete effectuee a la microsonde electronique, afin de preciser les variations de teneurs de Rb, K, Al et F. Les resultats indiquent qu'il existe une relation lineaire decroissante entre les rapports [Rb/K] des micas et leurs teneurs en Al VI . L'interpretation est fondee sur l'hypothese que le coefficient de partage C Rb/K mica/fl entre fluide et mineral ne varie pratiquement pas avec la temperature et la pression dans les conditions etroites de cristallisation des pegmatites. On montre que la relation obtenue, C Rb/K mica/fl =0,55×(5−[Al VI ]), est d'ordre cristallochimique. Les micas a faibles teneurs en Al admettent de plus grandes teneurs en Rb, car les sites potassiques d'accueil de Rb sont plus grands. Cette relation fournit un autre moyen de calculer les valeurs [Rb/K] des fluides, connaissant Rb, K, Al et Si des micas. Cette cristallochimie permet aussi de prevoir une correlation directe entre Rb et F dans les micas pegmatitiques. Pour citer cet article : J. Quemeneur et al., C. R. Geoscience 336 (2004).

Since conventional anti-slip enamels show some disadvantages, directly related to the surface roughness which prevents the adequate surface cleaning of tile, an anti-slip enamel exhibiting glass-ceramic nature has been designed, characterized by being stain-resistant and presenting a smooth texture and touch soft. To do this, new matte frits and raw materials with similar nature have been used, refractory enough to be suitable in enamel compositions for porcelain stoneware. The glass-ceramic glaze thus prepared was characterized by various instrumental techniques (X-ray fluorescence [XRF], scanning electron microscopy [SEM], X-ray diffraction [XRD], mechanical profilometry and microhardness measurements), in order to check the nature of crystallized phases, their morphology, surface roughness and microhardness of the finished tile. In addition, the quality of the glazed piece has been evaluated by the regulations of chemical resistance, stain-resistance and slipperiness. The enamel obtained has devitrified in crystals of silicoaluminates of calcium and barium and complies with standards of anti-slip and stain-resistence, as it has a surface roughness similar to a non-slip enamel. Dada la problemática que presentan los esmaltes antideslizantes convencionales, los cuales poseen una rugosidad superficial que dificulta la limpieza de la superficie de la pieza, se ha diseñado un esmalte antideslizante de naturaleza vitrocerámica que es resistente a las manchas y presenta una textura lisa, de tacto suave. Para ello, se han utilizado nuevas fritas de naturaleza mate y materias primas de composiciones similares, suficientemente refractarias para ser adecuadas para esmaltar piezas de gres porcelánico. El esmalte vitrocerámico así obtenido se ha caracterizado a través de varias técnicas instrumentales (fluorescencia de rayos X [FRX], microscopia electrónica de barrido [MEB], difracción de rayos X [DRX], perfilometría mecánica y medidas de microdureza) con el fin de comprobar la naturaleza de las fases cristalizadas, su morfología, la rugosidad superficial y la microdureza de la pieza acabada. Además, se ha valorado la calidad de la pieza esmaltada mediante las normativas de resistencia química, resistencia a las manchas y resistencia a la resbaladicidad. El esmalte obtenido ha desvitrificado en cristales de silicoaluminatos de calcio y bario, cumple la normativa de antideslizamiento y es resistente a las manchas, ya que presenta una rugosidad superficial similar a un esmalte no antideslizante. Los autores agradecen a la empresa Colores Cerámicos S.A. de Onda (Castellón) las facilidades ofrecidas para la realización del presente trabajo.