Готові списки джерел за темами / Phase spinelle

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Добірка наукової літератури з теми "Phase spinelle"

Автор: Grafiati
Опубліковано: 23 вересня 2022
Оновлено: 27 січня 2023

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Статті в журналах з теми "Phase spinelle"

1

ALEKSEEV, Aleksandr Valer’evich, and Tat’yana Andreevna SHERENDO. "Composition, structure and magnetic properties of ore chrome spinels of the Klyuchevsky massif (Middle Urals)." NEWS of the Ural State Mining University 1, no. 1 (March 23, 2020): 73–85. http://dx.doi.org/10.21440/2307-2091-2020-1-73-85.

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Анотація:
The overall objective was to create a geological and geophysical field test site for chromite mineralization and detailed works in order to determine and test the main search criteria for disseminated mineralization. To create a field test site, an area was selected in the southern part of the Klyuchevsky massif characterized by abundant development of disseminated mineralization in the banded dunite-clinopyroxenite complex and strong processes of superimposed metamorphism. This paper gives a piece of research on the composition of chrome spinel from disseminated ores that underwent metamorphism of different stages. The composition of chrome spinelide, the evolution of its metamorphism and the related changes in its magnetic properties are examined in detail. It was established that all chrome spinels are of a high-chromium type, to one degree or another, they were subject to secondary changes, leading to the appearance of magnetic phases. The degree and nature of the change in chrome spinels in dunites directly depends on the degree of metamorphism of the rocks. The formation of the magnetic phase begins with the formation of nuclei consisting of single magnetic dipoles, groups of 2-3 dipoles or chains of magnetic dipoles, which was first discovered by us in chrome spinel grains. Then there is an increase in the number of such phases, the appearance of optically diagnosed secondary changes in chrome spinelide. A comparison of the degree of variation of chrome spinel and its reflection in the pattern of recorded anomalies of geomagnetic fields allows us to identify some criteria for the search for disseminated chromite ores of this type.
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2

Anderson, Ian M., Arnulf Muan, and C. Barry Carter. "Microstructural observations of the “Wustite-Spinel” coexistence following quenching of cation-excess spinels, Ni2(1+x)Ti1-xO4." Proceedings, annual meeting, Electron Microscopy Society of America 48, no. 4 (August 1990): 1058–59. http://dx.doi.org/10.1017/s0424820100178422.

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Анотація:
Oxide mixtures which feature a coexistence of phases with the wüstite and spinel structures are considered model systems for the study of solid-state reaction kinetics, phase boundaries, and thin-film growth, and such systems are especially suited to TEM studies. (In this paper, the terms “wüstite” and “spinel” will refer to phases of those structure types.) The study of wüstite-spinel coexistence has been limited mostly to systems near their equilibrium condition, where the assumptions of local thermodynamic equilibrium are valid. The cation-excess spinels of the type Ni2(1+x)Ti1-xO4, which reportedly exist only above 1375°C4, provide an excellent system for the study of wüstite-spinel coexistence under highly nonequilibrium conditions. The nature of these compounds has been debated in the literature. X-ray and neutron powder diffraction patterns have been used to advocate the existence of a single-phase, non- stoichiometric spinel. TEM studies of the microstructure have been used to suggest equilibrium coexistence of a stoichiometric spinel, Ni2TiO4, and a wüstite phase; this latter study has shown a coexistence of wüstite and spinel phases in specimens thought to have been composed of a single, non- stoichiometric spinel phase. The microstructure and nature of this phase coexistence is the focus of this study. Specimens were prepared by ball-milling a mixture of NiO and TiO2 powders with 10 wt.% TiO2. The mixture was fired in air at 1483°C for 5 days, and then quenched to room temperature. The aggregate thus produced was highly porous, and needed to be infiltrated prior to TEM sample preparation, which was performed using the standard techniques of lapping, dimpling, and ion milling.
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3

Saveliev, D. E. "Morphological and Compositional Features of Chromian Spinel from Mantle Ultramafic Rocks of The Nurali Massif (South Urals)." МИНЕРАЛОГИЯ (MINERALOGY) 5 (December 27, 2019): 3–18. http://dx.doi.org/10.35597/2313-545x-2019-5-4-1.

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Анотація:
Accessory chromian spinels of lherzolites and dunites from a mantle section of the Nurali ophiolite massif are described in the paper. Lherzolites typically host anhedral chromian spinel grains associated with olivine, pyroxenes and plagioclase. The compositions of silicates and chromian spinels are typical of those from ophiolite mantle sections. Olivine and orthopyroxene are characterized by high Mg content (forsterite and enstatite); clinopyroxene is diopside. The compositions of chromian spinel on the Al–Cr–Fe+3 plot occur close to the Al–Cr side. The #Cr and #Mg values of chromian spinels increase from lherzolites to dunites. Both vermicular spinels trapping olivine and orthopyroxene fragments (type I) and symplectite-like intergrowths of chromian spinel and plagioclase (type II) are most genetically interesting. Type I formed during synkinematic growth in deformed silicate matrix. Type II possibly formed as a result of decompression breakdown of a high-P mineral phase enriched in Cr, Al and Ca (a knorringite-type garnet?). In dunites, numerous tiny chromian spinel rods (type IV) in plastic deformed olivine are observed along with typical euhedral chromian spinel (type III) with inclusions of olivine and pargasite. Latter ones locally occur closely to fne pargasite grains. The formation of chromian spinel rods is explained as a result deformation-induced segregation of trace elements on the structural defects of the olivine lattice. Figures 7. Tables 4. References 48.
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4

Jastrzębska, Ilona, Wiktor Bodnar, Kerstin Witte, Eberhard Burkel, Paweł Stoch, and Jacek Szczerba. "Structural properties of Mn-substituted hercynite." Nukleonika 62, no. 2 (June 27, 2017): 95–100. http://dx.doi.org/10.1515/nuka-2017-0013.

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Анотація:
Abstract In this work spinel series with the general formula Fe1-xMnxAl2O4 (where x = 0, 0.3, 0.5 and 0.7) were synthesized and characterized with respect to their structure and microstructure. X-ray diffractometry (XRD) was used to identify the phase composition that revealed a single phase spinel material. Rietveld refinements of the XRD patterns were carried out in order to determine the lattice and oxygen positional parameters of the spinel compounds. Mössbauer effect measurements were performed at room temperature to determine the local chemical environment of the Fe ions, their valences, and degrees of spinels inversion. It was shown that an increase in the Mn content led to a decrease in the ratio of Fe2+ to Fe3+. The results obtained from Mössbauer spectroscopy (MS) were used to establish the chemical formulas of the synthesized spinels. Finally, the microstructure that was observed using scanning electron microscopy (SEM) showed a compact microstructure with an octahedral crystal habit.
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5

Zaitseva, O. V., Vladimir E. Zhivulin, and D. E. Zhivulin. "The Creation of Multicomponent Octahedral Crystals with Spinel Structure Using Solid-Phase Synthesis in the Al2O3-BaO-CuO-Fe2O3-Mn2O3-NiO-SrO-TiO2- ZnO and Al2O3-BaO-CuO-Fe2O3-NiO-SrO-TiO2-WO3- ZnO Systems." Materials Science Forum 989 (May 2020): 341–46. http://dx.doi.org/10.4028/www.scientific.net/msf.989.341.

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Анотація:
This paper presents the results of an experimental study of the possibility of high-entropy oxide phases creation using the of solid-phase synthesis method in the Al2O3–BaO–CuO–Fe2O3–Mn2O3–NiO–SrO–TiO2–ZnO and Al2O3–BaO–CuO–Fe2O3–NiO–SrO–TiO2–WO3–ZnO systems. As a result of the study, a microcrystalline octahedral multicomponent phase was found in the crystallized sample. Judging by the composition, this phase has a spinel structure and is characterized (judging by the components concentrations and its ratio) by rather high values of the mixing configurational entropy. It is shown that barium, strontium and tungsten are not included in this phase in appreciable amounts. The obtained results indicate the possibility of synthesizing high-entropic spinels using these Al2O3–CuO–Fe2O3–Mn2O3–NiO–TiO2–ZnO systems.
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6

Talanov, V. M., V. B. Shirokov, and M. V. Talanov. "Unique atom hyper-kagome order in Na4Ir3O8and in low-symmetry spinel modifications." Acta Crystallographica Section A Foundations and Advances 71, no. 3 (April 25, 2015): 301–18. http://dx.doi.org/10.1107/s2053273315003848.

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Анотація:
Group-theoretical and thermodynamic methods of the Landau theory of phase transitions are used to investigate the hyper-kagome atomic order in structures of ordered spinels and a spinel-like Na4Ir3O8crystal. The formation of an atom hyper-kagome sublattice in Na4Ir3O8is described theoretically on the basis of the archetype (hypothetical parent structure/phase) concept. The archetype structure of Na4Ir3O8has a spinel-like structure (space group Fd\bar 3m) and composition [Na1/2Ir3/2]16d[Na3/2]16cO32e4. The critical order parameter which induces hypothetical phase transition has been stated. It is shown that the derived structure of Na4Ir3O8is formed as a result of the displacements of Na, Ir and O atoms, and ordering of Na, Ir and O atoms, orderingdxy,dxz,dyzorbitals as well. Ordering of all atoms takes place according to the type 1:3. Ir and Na atoms form an intriguing atom order: a network of corner-shared Ir triangles called a hyper-kagome lattice. The Ir atoms form nanoclusters which are named decagons. The existence of hyper-kagome lattices in six types of ordered spinel structures is predicted theoretically. The structure mechanisms of the formation of the predicted hyper-kagome atom order in some ordered spinel phases are established. For a number of cases typical diagrams of possible crystal phase states are built in the framework of the Landau theory of phase transitions. Thermodynamical conditions of hyper-kagome order formation are discussed by means of these diagrams. The proposed theory is in accordance with experimental data.
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7

Kostuch, Aldona, Joanna Gryboś, Szymon Wierzbicki, Zbigniew Sojka, and Krzysztof Kruczała. "Selectivity of Mixed Iron-Cobalt Spinels Deposited on a N,S-Doped Mesoporous Carbon Support in the Oxygen Reduction Reaction in Alkaline Media." Materials 14, no. 4 (February 9, 2021): 820. http://dx.doi.org/10.3390/ma14040820.

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Анотація:
One of the practical efforts in the development of oxygen reduction reaction (ORR) catalysts applicable to fuel cells and metal-air batteries is focused on reducing the cost of the catalysts production. Herein, we have examined the ORR performance of cheap, non-noble metal based catalysts comprised of nanosized mixed Fe-Co spinels deposited on N,S-doped mesoporous carbon support (N,S-MPC). The effect of the chemical and phase composition of the active phase on the selectivity of catalysts in the ORR process in alkaline media was elucidated by changing the iron content. The synthesized materials were thoroughly characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy (RS). Detailed S/TEM/EDX and Raman analysis of the phase composition of the synthesized ORR catalysts revealed that the dominant mixed iron-cobalt spinel is accompanied by minor fractions of bare cobalt and highly dispersed spurious iron oxides (Fe2O3 and Fe3O4). The contribution of individual phases and their degree of agglomeration on the carbon support directly influence the selectivity of the obtained catalysts. It was found that the mixed iron-cobalt spinel single phase gives rise to significant improvement of the catalyst selectivity towards the desired 4e− reaction pathway, in comparison to the reference bare cobalt spinel, whereas spurious iron oxides play a negative role for the catalyst selectivity.
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8

Zhang, Zhibin, Fei Huang, Yongli Li, Kaijun Liu, and Fude Zhao. "Nano-Micron Exsolved Spinels in Titanomagnetite and Their Implications for the Formation of the Panzhihua Fe–Ti–V Oxide Deposit, Southwest China." Journal of Nanoscience and Nanotechnology 21, no. 1 (January 1, 2021): 326–42. http://dx.doi.org/10.1166/jnn.2021.18448.

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Анотація:
The nano-micron exsolved spinels with various mineralogical characteristics in titanomagnetite from Fe–Ti oxide gabbros in the Panzhihua Fe–Ti–V oxide deposit, SW China, have been studied by field emission scanning electron microscopy (FE-SEM) and electron probe microanalysis (EPMA) based on comparisons of physical and chemical conditions at different stratigraphic heights to investigate the compositional inheritance between titanomagnetite and exsolved spinel and further explore the relationship between the morphology and growth of exsolved spinels. Restored chemical data for titanomagnetite combined with evidence from petrography and whole-rock geochemistry imply fractional crystallization of the Panzhihua Fe–Ti–V oxide deposit, where the titanomagnetite of thick massive oxides at the bottom of the No. VIII orebody represents the early crystallizing phase characterized by high temperature and oxygen fugacity. The chemical variation in the exsolved spinel, which has the same trend as the restored composition of titanomagnetite, represents inheritance from the parent rock within the Panzhihua deposit. Exsolved spinel continuously adjusts morphology and grain size to decrease the total energy of the manganate-spinel system from fine-grained spinels parallel to the {100} plane of titanomagnetite to spinels with complex stellate morphology to bulky granular spinels with high degrees of idiomorphism. The unusual multiple magma replenishment during the mineralizing process and at different stratigraphic heights in the Panzhihua intrusion had an important influence on the thermal evolution history of the orebody, resulting in the identifiable spatial distribution patterns of spinel morphology and grain size. Using spinel exsolution as a discriminator for the provenance of magmatic ore deposits may provide intuitive and easy mineralogical evidence to qualitatively discuss the evolution of the metallogenetic environment and the ore-forming conditions for similar large mafic intrusions.
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9

Skvortsova, Vera, Nina Mironova-Ulmane, and Daina Riekstiņa. "Structure and Phase Changes in Natural and Synthetic Magnesium Aluminum Spinel." Environment. Technology. Resources. Proceedings of the International Scientific and Practical Conference 2 (August 5, 2015): 100. http://dx.doi.org/10.17770/etr2011vol2.1002.

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Анотація:
Natural spinel crystals from Ural and Pamir deposits and synthetic magnesium aluminium spinel single crystals with different stoichiometry (MgO.nAl2O3 ) grown by Verneuil method were used. The photoluminescence (PL), its excitation (PLE) and optical absorption of stoichiometric and nonstoichiometric magnesium aluminium spinel crystals containing the chromium and manganese ions and defects produced by fast neutron irradiation( fluence up to 1020cm-2, E>0.1 MeV) are investigated. The broadening of R- and N-lines takes place in synthetic stoichiometric spinel. Structure of synthetic nonstoichiometric spinels (n>1) has to be more disordered, since in addition to the site exchange the so called stoichiometric vacancies are present in the structure. The R- and N-lines broadening takes place after spinel crystals irradiation by fast neutron too. The neutron irradiation causes increasing of the spinel inversion. Furthermore the great deviation from stoichiometry leads to the local structure of α-Al2O3 formation around Cr3+ ions. The orange emission band at 570 nm is belonging to complex center “Mn2+-F+ (or F centre)”.
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10

Reimann, T., J. Töpfer, and S. Barth. "Low-temperature sintered NTC ceramics for thick film temperature sensors." Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2012, CICMT (September 1, 2012): 000536–41. http://dx.doi.org/10.4071/cicmt-2012-wp42.

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Анотація:
Printed thick film NTC thermistors and multilayer devices are frequently used for temperature control in hybrid circuits. NiMn2O4 and substituted spinels are the most established materials for this application. For low-temperature sintering at 900 °C the shrinkage behavior of the thermistor material has to be adjusted by the addition of proper sinter additives. We investigated the chemical stability of NiMn2O4 and substituted spinels in air between 25 °C and 1200 °C. The compound NiMn2O4 is stable from 700 °C to 970 °C only and interacts with the sinter additives. Stable cubic spinels were found in the system ZnxNi0,5Co0,5Mn2-zO4. Addition of liquid phase sintering additives to the spinel powders results in complete densification at 900 °C. No chemical interaction between spinel and additive was observed. The effect of Cu-substitution into the spinel was also investigated. Functional NTC pastes were printed on alumina substrates and post-fired at 900 °C. The NTC thermistor films have a sheet resistivity of about 300 kOhm/sq and B = 3300 K. The firing behavior, microstructure formation and electric properties of NTC thick films will be reported.
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Більше джерел

Дисертації з теми "Phase spinelle"

1

Hébert, Christian. "Films minces nanocomposites ZnxFe1-xO1+δ : phases wurtzite, sel gemme et spinelle". Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066068/document.

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Анотація:
Cette thèse porte sur la croissance de films minces d’oxydes de zinc/fer (ZnxFe1-xO1+δ par ablation laser pulsée (PLD) et sur la possibilité de contrôler leurs propriétés structurales et physico-chimiques en variant les conditions d’élaboration : pression d’oxygène et température de croissance, proportions respectives de zinc/fer. Pour de fortes valeurs de x (x > 65%), les films sont monophasés de structure wurtzite type ZnO (films Fe:ZnO), avec une transparence optique dans la gamme UV-visible de 80% mais sans propriété ferromagnétique ; en fonction de leur teneur en fer (1-x), ils évoluent de très bons conducteurs électriques à quasi-isolants. Pour de faibles valeurs de x (x < 15%), les films sont également monophasés de structure spinelle type Fe3O4 (films Zn:Fe3O4). Ils présentent de très bonnes propriétés ferromagnétiques dès la température ambiante ainsi qu’une bonne conductivité électrique, les effets de localisation des porteurs de charge se manifestant en dessous de la température de Verwey. Le nombre de parois d’antiphase peut être diminué par une croissance en deux étapes, comme l’atteste les mesures de magnétorésistance. Aux taux intermédiaires de zinc (15% < x < 65%), les films sont nano-composites. Dans le cas d’une coexistence des phases Fe:ZnO et Zn:Fe3O4, la bonne conductivité de Zn:Fe3O4 jointe à la multiplicité des variantes épitaxiales et donc des interfaces fournit un matériau adapté à la thermoélectricité. Dans le cas d’une coexistence de la phase ferrromagnétique Zn:Fe3O4 avec la phase Zn:FeO antiferromagnétique de type sel gemme, un fort couplage d’échange ainsi qu’une anisotropie magnétique perpendiculaire élevée sont mis en évidence
This thesis deals with the growth of thin films of zinc/iron oxides (ZnxFe1-xO1+δ) by pulsed laser deposition (PLD) and the possibility of controlling their structural and physicochemical properties by varying the elaboration conditions: oxygen pressure and growth temperature, respective proportions of zinc/iron. For high values of x (x> 65%), the films are single-phase with a ZnO-type wurtzite structure (Fe:ZnO films), with 80% optical transparency in the UV-visible range but without ferromagnetic properties; depending on their iron (1-x) content, they evolve from very good electrical conductors to near-insulators. For small values of x (x <15%), the films are also single-phase with a Fe3O4-type spinel structure (Zn:Fe3O4 films). They exhibit very good ferromagnetic properties at ambient temperature as well as good electrical conductivity, the localization effects of charge carriers occurring below the Verwey temperature. The number of antiphase walls can be decreased by a two-step growth, as evidenced by magnetoresistance measurements. At intermediate zinc rates (15%
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2

Condolf, Cyril. "Elaboration d’un cermet conducteur électrique à haute température." Grenoble INPG, 2005. http://www.theses.fr/2005INPG0071.

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Анотація:
Cette thèse est consacrée à l'élaboration de matériaux d'anode inerte, utilisés pour l'électrolyse de l'aluminium. A partir de connaissances acquises sur le cermet cuivre-ferrite de nickel, une stratégie de recherche a été menée afin de proposer des systèmes chimiques alternatifs. La lecture des diagrammes de phases constitue en ce sens un outil de prédiction des compositions potentiellement pertinentes. Des modèles physiques de conductivité du spinelle et de frittage, intégrés aux résultats du calcul thermodynamique, sont utilisés pour déterminer des zones préférentielles théoriques d'élaboration d'un cermet, dans le système Al-Co-Cr-Fe-Ni-Zn-0 (base de données FACT). Le manganèse, comparable au fer au cobalt par sa structure électronique, ne fait pas partie de la base FACT, et le diagramme Fe-Mn-Ni-0 a dû être étudié expérimentalement et théoriquement pour l'inclure dans la réflexion et montrer son intérêt comme élément d'alliage. L'application pratique a été validée dans le cas de matériaux Cu-Al-Fe-Ni-0 et Cu-Fe-Mn-Ni-O. L'ajout d'aluminium réduit la solubilité dans le bain cryolithique, et le manganèse peut être utilisé comme dopant afin de favoriser le frittage. L'intérêt potentiel des autres éléments (Co,Cr et Zn) a été abordé par la logique déductive développée au cours de cette thèse
This thesis is devoted to the making of inert anode materials, used for aluminium electrolysis. On the basis of knowledge obtained from the cermet copper- nickel ferrite, a strategy of research was carried out in order to determine alternative chemical systems. The reading of phase diagrams is a tool of prediction for hypothetical promising compositions. Physical models of spinel conductivity and sintering, integrated into the results of thermodynamic calculation, are used to determine theoretical best zones of cermets'development, in the system Al-Co-Cr-Fe-Ni-Zn-O (FACT database). Manganese, comparable with iron and cobalt concerning the electronic structure, is not included in FACT database and Fe-Mn-Ni-0 had to be evaluated through experiments and theoretically in order to include it in our thought and to show its interest as an alloying element. Practical application was validated in the case of Cu-Al-Fe-Ni-0 and Cu-Fe-Mn-Ni-0 materials. Addition of aluminium reduces the solubility in cryolite bath, and manganese can be used as a doping element in order to enhance sintering. The potential interest of the other elements (Co,Cr and Zn) has been surveyed through a logical analysis developed during the thesis
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3

Tabit, Adelhalim. "Equilibre orthopyroxene-spinelle : etude experimentale et theorique, application aux roches issues du manteau superieur." Clermont-Ferrand 2, 1986. http://www.theses.fr/1986CLF21025.

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Анотація:
Le travail concerne l'equilibre orthopyroxene-spinelle dans les lherzolites a spinelle, roches caracteristiques du manteau superieur. L'etude mineralogique d'echantillons naturels montre que les teneurs en aluminium et en chrome dans l'orthopyroxene varient avec la texture de l'echantillon, la composition globale du systeme et les conditions de temperature controlant les phases de deformation cristallisation. Le comportement des elements di- et triavalents dans l'equilibre orthopyroxene-spinelle peut etre utilise a des fins geovelocimetriques. Les resultats obtenus lors de l'etude experimentale du systeme simplifie cr::(2)o::(3)-mgo-al::(2)o::(3)-sio::(2) ont fait l'objet d'un traitement mathematique par methode d'inversion generalisee. On obtient ainsi une equation geothermometrique applicable aux roches ultrabasiques du facies lherzolite a spinelle: t4(k)=(61490-16000(y::(crsp))**(2))/(27-8,314lnkd)
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4

Douin, Myriam. "Etude de phases spinelle cobaltées et d'oxydes lamellaires dérivés de Na0,6CoO2 employés comme additifs conducteurs dans les accumulateurs Ni-MH." Bordeaux 1, 2008. http://www.theses.fr/2008BOR13562.

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Анотація:
La technologie mousse utilisée actuellement pour la conception des électrodes positives des batteries Ni-MH, nécessite l'emploi d'un additif conducteur au cobalt en raison de la mauvaise conductivité électronique de la matière active Ni(OH)2. La recherche de nouveaux composés au cobalt constitue un point clé en vue du développement de ces batteries vers des applications de forte puissance. Dans ce contexte, deux additifs conducteurs potentiels ont été étudiés au cours de ces travaux de thèse. La première partie de l'étude a été focalisée sur des phases spinelle HxLiyCo3-8O4 conductrices, synthètisées par oxydation électrochimique de l'oxyde CoO. Une forte influence du traitement thermique du matériau sur sa conductivité électronique a été mise en évidence. Des analyses par diffraction des rayons X in situ, ATG-SM, RMN et des mesures de conductivités électroniques ont permis de mettre en évidence une redistribution catonique au sein de la structure spinelle, conduisant à une augmentation du rapport atomique Co4+/Co3+ dans le réseau octaédrique [Co2O4], sans variation du degré d'oxydation moyen du cobalt. Il s'ensuit une augmentation de la conductivité elctronique du matériau de trois ordres de grandeur. Le second axe de la thèse concerne l'étude du comportement électrochimique de l'additif Na0,6CoO2. Les réactions échange/insertion des ions alcalins mises en jeu au cours des processus d'oxydation et de réduction de la phase initiale ont été étudiées en détail et un mécanisme a pu être proposé. L'oxyhydroxyde de cobalt hydraté γ, formé par oxydation de Na0,6CoO2 au cours du cyclage, s'est avéré présenter de très bonnes performances lors de tests en batteries. La formation d'une phase interstratifiée intermédiaire, qui possède une cinétique de réduction lente, permet de conserver la stabilité de l'additif à bas potentiel et par conséquent, l'intégralité du réseau conducteur.
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5

Caillot, Thierry. "Synthèses microondes et caractérisation de nanoparticules associant une phase métallique M (M=Fe, FeCo, FeNi) et un oxyde de structure spinelle Fe3-xM'xO4(M'=Fe, Co, Ni, Mn, MnZn)." Dijon, 2002. http://www.theses.fr/2002DIJOS055.

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6

Madon, Michel. "Cellules à enclumes de diamant et microscopie électronique en transmission : étude expérimentale des transformations de phase du manteau terrestre." Paris 6, 1986. http://www.theses.fr/1986PA066123.

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Changements de phase associés aux discontinuités sismiques de 400 et 700km et conséquences sur la rhéologie du manteau. Etude des transitions polymorphiques entre les trois structures alpha , beta et gamma que peut prendre l'olivine et la décomposition de spinelle en pérovskite et magnésiowüstite. Etude réalisée en microscopie électronique en transmission sur des échantillons provenant de météorites choquées ou synthétisées à très haute pression et température dans une cellule à enclume de diamant.
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Douin, Myriam. "Etude de phases spinelle cobaltée et d'oxydes lamellaires dérivés de Na0,6CoO2 employés comme additifs conducteurs dans les accumulateurs Ni-MH." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2008. http://tel.archives-ouvertes.fr/tel-00373899.

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La technologie mousse utilisée actuellement pour la conception des électrodes positives des batteries Ni-MH, nécessite l'emploi d'un additif conducteur au cobalt en raison de la mauvaise conductivité électronique de la matière active Ni(OH)2. La recherche de nouveaux composés au cobalt constitue un point clé en vue du développement de ces batteries vers des applications de forte puissance. Dans ce contexte, deux additifs conducteurs potentiels ont été étudiés au cours de ces travaux de thèse.
La première partie de l'étude a été focalisée sur des phases spinelle HxLiyCo3-δO4 conductrices, synthétisées par oxydation électrochimique de l'oxyde CoO. Une forte influence du traitement thermique du matériau sur sa conductivité électronique a été mise en évidence. Des analyses par diffraction des rayons X in situ, ATG-SM, RMN et des mesures de conductivités électroniques ont permis de mettre en évidence une redistribution cationique au sein de la structure spinelle, conduisant à une augmentation du rapport atomique Co4+/Co3+ dans le réseau octaédrique [Co2O4], sans variation du degré d'oxydation moyen du cobalt. Il s'ensuit une augmentation de la conductivité électronique du matériau de trois ordres de grandeur. Le second axe de la thèse concerne l'étude du comportement électrochimique de l'additif Na0.6CoO2. Les réactions d'échange/insertion des ions alcalins mises en jeu au cours des processus d'oxydation et de réduction de la phase initiale ont été étudiées en détail et un mécanisme a pu être proposé. L'oxyhydroxyde de cobalt hydraté γ, formé par oxydation de Na0.6CoO2 au cours du cyclage, s'est avéré présenter de très bonnes performances lors des tests en batteries. La formation d'une phase interstratifiée intermédiaire, qui possède une cinétique de réduction lente, permet de conserver la stabilité de l'additif à bas potentiel et par conséquent, l'intégrité du réseau conducteur.
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8

Djian, Damien. "Etude et développement de séparateurs pour une nouvelle architecture de batteries Li-ion à charge rapide." Phd thesis, Grenoble INPG, 2005. http://tel.archives-ouvertes.fr/tel-00011543.

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Dans le cadre du développement de technologies innovantes dans le domaine des accumulateurs Li-ion à charge rapide, typiquement inférieure à 5 minutes, des séparateurs commerciaux ont été caractérisés par différentes méthodes physico-chimiques et électrochimiques afin de corréler leurs structures poreuses aux performances en charge rapide enregistrées. L'architecture d'électrode choisie utilise l'oxyde de titane Li4Ti5O12 à l'électrode négative et le spinelle LiMn2O4 à la positive.
Afin d'augmenter les capacités chargées par rapport aux séparateurs commerciaux, des membranes à squelette poly(fluorure de vinylidène) et poly(fluorure de vinylidène) co poly(hexafluoropropylène) ont été élaborées par inversion de phase en utilisant la méthodologie des plans d'expériences. Les processus de formation ont été explicités à partir de la thermodynamique des systèmes ternaires polymère/solvant/non-solvant. Les membranes obtenues ont permis de gagner 20% de capacité chargée en 3 minutes par rapport aux séparateurs commerciaux.
Enfin, les limitations en charge rapide dues aux séparateurs ont été étudiées et identifiées à l'aide d'un code de modélisation d'accumulateurs Li-ion.
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BENOIT, VINCENT. "Etat d'equilibre de peridotites du manteau superieur : application au plateau du colorado." Paris 7, 1987. http://www.theses.fr/1987PA077186.

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Deux nouvelles calibrations de methodes thermobarometriques a partir de donnees experimentales. La premiere basee sur la solubilite de diopside entre clinopyroxene et orthopyroxene. Elle prend en compte l'effet d'elements mineurs tels que na et fe. Ce thermobarometre, combine avec le thermometre base sur la solubilite de l'enstatite dans les deux pyroxenes fournit un bon outil pour tester l'etat d'equilibre des peridotites a spinelle. La deuxieme calibration est basee sur la solubilite du chrome dans la spinelle et le grenat coexistants
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10

Dinh, Thi Mong Cam. "Influence des conditions d'élaboration sur les transformations de phases dans les couches minces de cobaltites de fer à structure spinelle." Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30090.

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Des films minces spinelles de cobaltites de fer Co1,7Fe1,3O4 dont la composition se situe dans la lacune de miscibilité du diagramme de phases CoFe2O4-Co3O4, ont été préparés par pulvérisation cathodique RF au voisinage de la température ambiante. Les films obtenus, dont les épaisseurs de 300 nm ont été fixées, sont constitués de cristallites de diamètre moyen proche de 20 nm. Le traitement à 600 °C pendant plusieurs heures de ces échantillons conduit à la formation de deux phases spinelles, en accord avec le diagramme de phases. Cette transformation a été clairement établie, à la fois par la diffraction des rayons X et la spectroscopie Raman. Dans les cobaltites de fer "massifs" de compositions proches ou identiques, une telle transformation est de type spinodal et se caractérise par une organisation pseudo-périodique à une échelle de quelques dizaines de nanomètres, de phases spinelles riches en fer et riches en cobalt. Dans le but de mettre en évidence cette organisation dans les couches minces, différentes études de microscopie ont été menées. Un procédé de préparation spécifique a même été développé pour découper des lames minces, parallèlement au plan de la couche, par la technique du faisceau d'ions focalisé (FIB). Les cristallites peuvent ainsi être observées et étudiées individuellement. Les analyses n'ont rien révélé cependant, et dans le meilleur des cas, c'est-à-dire pour les cristallites les plus grosses, seule la présence de deux zones de compositions différentes a pu être constatée. L'alternance pseudo-périodique attendue n'a donc pas pu être observée. Il semble ainsi que la taille nanométrique des cristallites empêche l'établissement d'une transformation spinodale telle qu'elle peut être mise en évidence dans les échantillons "massifs". L'observation d'anomalies de composition dans les joints de grains corrobore cette hypothèse qui suggère un effet " nano " sur la transformation de phase. Au cours du présent travail, il a été en outre constaté qu'en plus de la température et du temps de recuit, les conditions de pulvérisation ont également un impact important sur la formation et la décomposition des phases dans les couches minces. Bien que cette étude n'ait pas trouvé les conditions de dépôt qui conduisent directement à la formation de deux phases spinelles dès la pulvérisation, elle montre toutefois que certaines conditions permettent d'écourter les temps de recuit tout en abaissant les températures requises pour effectuer la transformation recherchée. Pour la première fois, des couches de cobaltites de fer ont été soumises à des traitements sous faisceau laser afin de provoquer des transformations de phases en leur sein. Il a été montré que la formation de deux spinelles à partir d'une couche monophasée peut être réalisée dans des temps très courts et sous de faibles puissances, compte tenu probablement d'une élévation rapide et importante de la température locale, due à l'absorption du faisceau laser. Les nombreux paramètres offerts par la machine de photolithogravure mise en œuvre (puissance, vitesse de balayage, incrément du balayage, focalisation...) n'ont pu être explorés de manière exhaustive au cours de cette étude. Cette dernière ne doit donc être considérée que comme un travail préliminaire. Les résultats qu'elle livre sont toutefois prometteurs et font émerger une nouvelle voie de traitement, permettant de réaliser simplement des transformations de phases dans les cobaltites de fer
Thin spinel films of Co1.7Fe1.3O4 iron cobaltites, whose composition is in the miscibility gap of the CoFe2O4-Co3O4 phase diagram, were prepared by RF sputtering near room temperature. The films obtained, whose thicknesses were fixed at 300 nm, consist of crystallites with a mean diameter close to 20 nm. The treatment of these samples at 600 °C for several hours leads to the formation of two spinel phases, in agreement with the phase diagram. This transformation was clearly established, both by X-ray diffraction and Raman spectroscopy. In "bulk" iron cobaltites of close or same compositions, such a transformation is of spinodal type and is characterized by a pseudo-periodic organization of rich iron and cobalt-rich spinel phases on a scale of a few tens of nanometers. In order to highlight this organization in the thin films, microscopy studies were carried out. A specific preparation process was even developed in order to cut in-plane thin sections, by the focused ion beam (FIB) technique. Crystallites can thus be observed and studied individually. The analyzes revealed, however, and in the best case (i.e. for the largest crystallites), the presence of only two zones of different compositions. The expected pseudo-periodic alternation could never be observed. It seems that the nanometric size of the crystallites, prevents the spinodal transformation which was highlighted in the "bulk" samples. The observation of local chemical anomalies in grain boundaries corroborates this hypothesis, which suggests a "nano" effect on phase transformation. For the present work, it was furthermore found that in addition to the temperature and the annealing time, the sputtering conditions also have a significant impact on the formation and decomposition of the phases in the thin films. Although this study did not find the deposition conditions that lead directly to the formation of two spinel phases after sputtering, it shows however that certain conditions shorten the annealing times while lowering the temperatures required to perform the targeted transformation. For the first time, iron cobaltite thin films were subjected to laser beam treatments to induce phase transformations within them. It was shown that the formation of two spinels from a single-phase film can be achieved in very short times and at low laser power, probably because of a rapid and high rise of local temperature, due to the absorption of the laser beam. The numerous parameters offered by the photolithography machine used (power, scanning speed, scanning increment, focusing, etc.) could not be exhaustively explored during this study. The latter should therefore be considered only as a preliminary work. The results, however, are promising and seem to bring out a new treatment route, allowing simple phase transformations in iron cobaltites
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Частини книг з теми "Phase spinelle"

1

Chakraborty, Akshoy Kumar. "Spinel Phase." In Phase Transformation of Kaolinite Clay, 207–34. New Delhi: Springer India, 2013. http://dx.doi.org/10.1007/978-81-322-1154-9_20.

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Chakraborty, Akshoy Kumar. "Spinel Phase: A Concise Review." In Mullite Formations, 481–557. New York: Jenny Stanford Publishing, 2021. http://dx.doi.org/10.1201/9781003031673-17.

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3

Chakraborty, Akshoy Kumar. "Topotaxy IN K-MK-AL/SI Spinel-Mullite Reaction Series." In Phase Transformation of Kaolinite Clay, 303–11. New Delhi: Springer India, 2013. http://dx.doi.org/10.1007/978-81-322-1154-9_24.

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4

Chakraborty, Akshoy Kumar. "Critical Analysis and Characterization of Spinel Phase." In Mullite Formations, 663–728. New York: Jenny Stanford Publishing, 2021. http://dx.doi.org/10.1201/9781003031673-21.

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Rodríguez-Hernández, P., and A. Muñoz. "Theoretical Ab Initio Calculations in Spinels at High Pressures." In Pressure-Induced Phase Transitions in AB2X4 Chalcogenide Compounds, 103–29. Berlin, Heidelberg: Springer Berlin Heidelberg, 2014. http://dx.doi.org/10.1007/978-3-642-40367-5_4.

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Al-Sharab, Jafar F., James Bentley, Amit Singhal, Ganesh Skandan, and Frederic Cosandey. "Tem Study of Nanostructured Magnesium Aluminate Spinel Phase Formation." In Ceramic Transactions Series, 165–74. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2012. http://dx.doi.org/10.1002/9781118407158.ch18.

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7

Besmann, Theodore M., Nagraj S. Kulkarni, Karl E. Spear, and John D. Vienna. "Predicting Phase Equilibria of Spinel-Forming Constituents in Waste Glass Systems." In Ceramic Transactions Series, 119–31. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2012. http://dx.doi.org/10.1002/9781118408438.ch11.

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8

Will, G., and J. Lauterjung. "The kinetics of the pressure induced olivine-spinel phase transition Mg2GeO4." In High‐Pressure Research in Mineral Physics: A Volume in Honor of Syun‐iti Akimoto, 177–86. Washington, D. C.: American Geophysical Union, 1987. http://dx.doi.org/10.1029/gm039p0177.

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9

Kanno, Ryoji, Osamu Yamamoto, Christian Cros, and Jean-Louis Soubeyroux. "Phase Transition and Ionic Conductivity of the Spinel System Li2−2xMg1+xCl4." In Solid State Batteries, 460–63. Dordrecht: Springer Netherlands, 1985. http://dx.doi.org/10.1007/978-94-009-5167-9_33.

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10

Ramasamy, M., S. Baumann, A. Opitz, R. Iskandar, J. Mayer, D. Udomsilp, U. Breuer, and M. Bram. "Phase Interaction and Distribution in Mixed Ionic Electronic Conducting Ceria-Spinel Composites." In Advances in Solid Oxide Fuel Cells and Electronic Ceramics II, 99–112. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2017. http://dx.doi.org/10.1002/9781119320197.ch9.

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Тези доповідей конференцій з теми "Phase spinelle"

1

Dubsky, J., K. Neufuss, and B. Kolman. "Phase Composition Changes in Annealed Plasma-Sprayed Zircon-Alumina Coatings." In ITSC 1997, edited by C. C. Berndt. ASM International, 1997. http://dx.doi.org/10.31399/asm.cp.itsc1997p0473.

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Abstract Phase transformations and/or decomposition of deposited compounds have an indisputable influence on materials properties of plasma sprayed deposits. Using water stabilized plasma, free-standing parts were manufactured from a mechanical mixture of zircon and alumina powders and annealed. The phase composition was determined by X-ray diffraction and the chemical composition was checked by x-ray microanalysis. ZrSiO4 during plasma spraying decomposes into ZrO2 and SiO2. In the as-sprayed condition, after a relatively fast quenching, the following phases can be found: a very fine eutectic mixture of tetragonal and monoclinic ZrO2, amorphous SiO2 and a spinel phase of Al2O3. On annealing for 2 hours at 1300 and 1500 °C the spinel Al2O3 transformed to corundum. At the same time, amorphous silica crystallized. Tetragonal ZrO2 transformed to the monoclinic modification and together with SiO2 formed again ZrSiO4. At the highest annealing temperature Al2O3 and SiO2 partialy reacted to form a small amount of mullite (3Al2O3.2SiO2).
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2

Stefanovsky, Sergey, Alexander Kobelev, Vladimir Lebedev, Michael Polkanov, Dmitriy Suntsov, and James Marra. "The Effect of Waste Loading on the Characteristics of Borosilicate SRS SB4 Waste Glasses." In ASME 2009 12th International Conference on Environmental Remediation and Radioactive Waste Management. ASMEDC, 2009. http://dx.doi.org/10.1115/icem2009-16196.

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The glasses containing surrogate of Sludge Batch 4 (SB4) waste with high concentrations of aluminum and ferrous oxides within the waste loading (WL) range of ∼50 to 70 wt.% produced in alumina crucibles in a resistive furnace and in a 236 mm inner diameter cold crucible were examined by X-ray diffraction, electron microscopy and infra-red spectroscopy. At relatively low WLs (50 to 60 w.%) the products remain predominantly vitreous with minor crystalline spinel structure phase corresponding in chemical composition to trevorite-magnetite solid solution. At higher WLs (&gt;60 wt.%) amount of crystalline phases increased significantly and a nepheline phase was observed. The products with WL of 65 to 70 wt.% were spinel/nepheline glass-ceramics. The glass with 60 wt.% WL slowly cooled in accordance with the canister centerline cooling (CCC) conditions contained minor nepheline. Occurrence of nepheline reduces the chemical durability of nuclear waste glasses.
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3

Schiller, G., M. Müller, F. Gitzhofer, M. I. Boulos, and R. B. Heimann. "Suspension Plasma Spraying (SPS) of Cobalt Spinel." In ITSC 1997, edited by C. C. Berndt. ASM International, 1997. http://dx.doi.org/10.31399/asm.cp.itsc1997p0343.

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Abstract Fine (median size 6 μm and 0.3 μm) cobalt spinel (Co3O4) powders were processed suspended in a suitable liquid phase. Suspensions exceeding 50 wt.% solid phase content were successfully injected into an inductively coupled plasma. Spheroidized powders with large particle size (up to 80 μm) were prepared, and cobalt oxide coatings were produced by this novel RF-SPS method. The microstructural features of the coatings can be controlled by parameter optimization similarly to plasma spraying of dry powders. Numerous variations of the physical and chemical conditions of the process were performed in an attempt to overcome the main disadvantage of the process, i.e. the decomposition of the spinel phase to CoO. So far, the spinel phase could be reestablished only by a post-treatment of the deposited coatings with atomic oxygen in the RF plasma.
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4

Bolelli, G., L. Lusvarghi, D. Lisjak, A. Hujanen, P. Lintunen, U. Kanerva, T. Varis, et al. "Thermally-Sprayed BaCoTiFe10O19 Layers as Microwave Absorbers." In ITSC2009, edited by B. R. Marple, M. M. Hyland, Y. C. Lau, C. J. Li, R. S. Lima, and G. Montavon. ASM International, 2009. http://dx.doi.org/10.31399/asm.cp.itsc2009p0628.

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Abstract This study shows that thermal spraying is a viable technique for the deposition of barium hexaferrite layers suitable for microwave absorption applications. More specifically, the study shows that impact quenching of molten BaCoTiFe10O19 hinders the crystallization of the hexaferrite phase. Consequently, when spraying conditions induce near-full melting of the feedstock, the coating mostly consists of spinel and a glassy phase, a state with poor magnetic properties. These phases can be converted to hexaferrite by annealing, but in order to obtain enough crystalline hexaferrite in as-deposited layers, a controlled amount of unmelted material must be preserved. Atmospheric plasma spraying proved to be well suited for this purpose, producing layers with excellent magnetic properties, close to those of pure crystalline BaCoTiFe10O19. In these coatings, dense regions entrain many unmelted agglomerates of micron-sized particles, effectively preserving the hexaferrite phase.
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Mueller, M., R. Henne, G. Schiller, M. I. Boulos, F. Gitzhofer, and R. B. Heimann. "Radio-Frequency Suspension Plasma Spraying of Cobalt Spinel Anodes for Alkaline Water Electrolysis." In ITSC 1998, edited by Christian Coddet. ASM International, 1998. http://dx.doi.org/10.31399/asm.cp.itsc1998p1523.

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Abstract Suspensions of cobalt spinel (Co3O4) powders (median size 6 µm and 0.3 µm) were r.f. plasma sprayed to form electrocatalytically active anode layers for alkaline water electrolysis. Stable cobalt oxide suspensions of low viscosity and exceeding 50wt.% solid phase content have been processed. A spheroidization study revealed the formation of large spherical powder particles (- 30 + 80 µm). Cobalt oxide coatings were produced by this novel r.f.-Suspension Plasma Spraying (SPS) method. The porosity was controlled by optimizing the spray distance and the reactor pressure. The main disadvantage of the thermal plasma processing of cobalt spinel, i.e. the decomposition of the spinel phase into CoO, could not be prevented, not even with the application of an 80% oxygen plasma. With a relatively low power oxygen plasma post-treatment the deposited CoO layers can be oxidized to Co3O4 resulting in a promising improvement of the electrochemical performance of the anode layers.
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Aoki, Hirofumi, Hiroshi Kaneko, Noriko Hasegawa, Hideyuki Ishihara, Yoichiro Takahashi, Akio Suzuki, and Yutaka Tamaura. "Two-Step Water Splitting With Ni-Ferrite System for Solar H2 Production Using Concentrated Solar Radiation." In ASME 2004 International Solar Energy Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/isec2004-65068.

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Two-step water splitting with Ni-ferrite (NiFe2O4) system for H2 production using concentrated solar thermal was examined. The O2 releasing reaction proceeded in air at 1800K by irradiation with Xe lamp beams which were used as a solar simulator. The stoichiometry and the reaction mechanism of the O2 releasing step were investigated by XRD. The reaction yield was estimated to be 48% from the calculation of the spinel phase lattice constant, and the XRD showed that the solid solution phase of (Ni, Fe)O between NiO and FeO was formed. The (Ni, Fe)O solid solution could lower the O2 releasing reaction temperature. In the H2 generating step for the sample obtained by the O2 releasing step, the reaction proceeded very fast and its yield was 90% of the theoretical one at 1123K. The XRD measurement indicated that the (Ni, Fe)O solid solution phase was changed to the spinel phase of Ni-ferrite in the H2 generation step.
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McCartney, D. G., D. Zhang, J. Y. Yellup, M. Brühl, K. Bobzin, K. Richardt, T. Talako, and A. Ilyushchanka. "Novel NiZn-Ferrite Powders and Coatings for Electromagnetic Applications." In ITSC2009, edited by B. R. Marple, M. M. Hyland, Y. C. Lau, C. J. Li, R. S. Lima, and G. Montavon. ASM International, 2009. http://dx.doi.org/10.31399/asm.cp.itsc2009p0818.

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Abstract This paper reports on the development of NiZn-ferrite powders and their deposition by air plasma and high-velocity oxyfuel spraying. The microstructure and phase composition of the powders and coatings are analyzed and the influence of process parameters on coating development is assessed for sprayed layers up to 500 μm thick. Particular attention is paid to the degradation of the spinel crystal structure, the formation of iron oxide phases, and elemental loss during spraying. The results show that a degree of ferrite decomposition occurs with the loss of zinc and formation of wüstite and that zinc loss is very dependent on the surface-to-volume ratio of the powder.
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Ondro, Tomáš, Štefan Csáki, František Lukáč, and Anton Trník. "Non-isothermal kinetic analysis of spinel phase crystallization from metakaolinite." In CENTRAL EUROPEAN SYMPOSIUM ON THERMOPHYSICS 2019 (CEST). AIP Publishing, 2019. http://dx.doi.org/10.1063/1.5120167.

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9

Kaur, Harleen, and M. M. Sinha. "Phonon dispersion and density of States of Fe2SiO4 in spinel phase." In ADVANCED MATERIALS AND RADIATION PHYSICS (AMRP-2020): 5th National e-Conference on Advanced Materials and Radiation Physics. AIP Publishing, 2021. http://dx.doi.org/10.1063/5.0052582.

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10

Ramis, Gianguido, Guido Busca, Tania Montanari, Michele Sisani, and Umberto Costantino. "Ni-Co-Zn-Al Catalysts From Hydrotalcite-Like Precursors for Hydrogen Production by Ethanol Steam Reforming." In ASME 2010 8th International Conference on Fuel Cell Science, Engineering and Technology. ASMEDC, 2010. http://dx.doi.org/10.1115/fuelcell2010-33034.

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A series of well crystallized Ni-Co-Zn-Al LDHs materials has been prepared by the urea hydrolysis method as precursors of mixed oxide catalysts for the Ethanol Steam Reforming (ESR) reaction. The calcination of the layered precursors gives rise to high surface area mixed oxides, mainly a mixture of rock-salt phase (NiO), wurtzite phase (ZnO) and spinel phase. Both precursors and mixed oxides have been throughtfully characterized and the steam reforming of ethanol has been investigated over the calcined catalysts in flow reactor and in-situ FT-IR experiments. The data here reported provide evidence of the good catalytic activity of Co-Zn-Al and Co-Ni-Zn-Al catalysts prepared from hydrotalcite-like LHD precursors for ethanol steam reforming. At 823 K the most active Co/Ni catalyst containains a predominant spinel phase with composition near Zn0.58Ni0.42[Al0.44Co0.56]2O4 and small amounts of NiO and ZnO. On the other side, at 873 K the selectivity to hydrogen increases with cobalt content. In particular, the presence of cobalt increases selectivity to H2 and CO2 and decreases selectivity to methane in the low temperature range 720–870 K. The most selective catalyst is the Ni-free Co-Zn-Al mixed oxide essentially constituted by a single spinel type phase Zn0.55Co0.45[Al0.45Co0.55]2O4. Cobalt catalysts appear consequently to behave better than nickel based catalysts in this temperature range. The key feature for high selectivity to hydrogen is proposed to be associated to a stability of a relatively high oxidation state at the catalyst surface, the most relevant selectivity determining step being constituted by the evolution of surface acetate species. In fact, over oxidized catalyst surface the acetate species evolve producing carbon dioxide and hydrogen while over a more reduced surface they evolve giving rise to methane and COx. Water is supposed to have the main role of allowing surface sites to stay in an unreduced state at least in the temperature range 720–870 K.
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Звіти організацій з теми "Phase spinelle"

1

Wouter Montfrooij. designer phase transitions in lithium-based spinels. Office of Scientific and Technical Information (OSTI), September 2011. http://dx.doi.org/10.2172/1042954.

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Harris, Donovan. Subsurface Optical Microscopy of Coarse Grain Spinels. Phase 1. Fort Belvoir, VA: Defense Technical Information Center, December 2013. http://dx.doi.org/10.21236/ada593527.

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Wogelius, R. A., and D. G. Fraser. Ga, Ca, and 3d transition element (Cr through Zn) partitioning among spinel-lherzolite phases from the Lanzo massif, Italy: Analytical results and crystal chemistry. Office of Scientific and Technical Information (OSTI), June 1994. http://dx.doi.org/10.2172/10154294.

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