Статті в журналах з теми "Phase spinelle"
Щоб переглянути інші типи публікацій з цієї теми, перейдіть за посиланням: Phase spinelle.
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся з топ-50 статей у журналах для дослідження на тему "Phase spinelle".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Переглядайте статті в журналах для різних дисциплін та оформлюйте правильно вашу бібліографію.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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)”.
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.
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.
11
Anderson, Ian M. "Crystal orientation effects in the x-ray microanalysis of spinels." Proceedings, annual meeting, Electron Microscopy Society of America 50, no. 2 (August 1992): 1240–41. http://dx.doi.org/10.1017/s0424820100130833.
Анотація:
Compounds with the crystal structure of the mineral spinel (MgAl2O4) provide an interesting test case for the quantitative x-ray microanalysis of crystals. The cations occupy more than one crystallographic site, two thirds occupying the octahedral 16d interstices and one third occupying the tetrahedral 8a interstices of the oxygen anion sublattice (Fd3m). Under dynamical electron diffraction conditions in the AEM, the standing-wave electron intensity on the two sublattices may differ considerably, in turn yielding proportionally different x-ray count rates from the cations on these sublattices. This effect has been exploited to determine the sites of impurity atoms in spinels using the ALCHEMI technique. The strong crystal orientation effect obstructs the accurate determination of the composition of spinels using x-ray microanalysis, however. In the system NiO-TiO2, which is the subject of ongoing investigation, a second phase is always found finely dispersed within the metastable spinel phase. The AEM is the only instrument which provides the high spatial resolution necessary to probe the composition.
12
Nguyen Xuan, Dung, and Huyen Phan Thi Minh. "Synthesis, characterizations and the photocatalytic ability of Co1-xZnxFe2O4 spinels prepared by combustion method." Vietnam Journal of Catalysis and Adsorption 10, no. 1S (October 15, 2021): 242–46. http://dx.doi.org/10.51316/jca.2021.130.
Анотація:
In this research, Co1-xZnxFe2O4 (x=0-0,5) spinel ferrites were synthesized at 5000C by combustion method using glycine and metal nitrates. The powder samples were characterized by thermogravimetric and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX). X-ray analysis showed that all samples have single phase cubic spinel structure. Structural parameters of spinels were also determined from XRD datas. The lattice constants, cell volumes increased with the increase in zinc substitution. The average crystallite sizes of the particles were determined with Zn content from 11 to 16 nm. The TEM images reveals the spherical shapes of nanoparticles with an average particle size less than 20 nm. The photocatalytic activity of the spinels were tested by the degradation of methylene blue (MB) in aqueous solution under visible light. The results showed that Zn doped spinels exhibited higher photocatalytic activity than CoFe2O4. Among all the samples, the maximum degradation efficiency was achieved by the 0.4 Zn substituted cobalt ferrite.
13
Magnago, Roberto de Oliveira, Fernanda de Assis Baião Miranda Pereira, Paula Cipriano da Silva, José Vitor Candido de Souza, and Claudinei dos Santos. "Infiltrated Spinel-Based Ceramic (MgAl2O4) for Dental Application." Materials Science Forum 881 (November 2016): 176–80. http://dx.doi.org/10.4028/www.scientific.net/msf.881.176.
Анотація:
This work developed a ceramic material for dental application, spinel-base (MgAl2O4), a ceramic material with recognized translucency. Spinel powders were uniaxially pressed at 100 MPa and pre-sintered in order to obtain porous ceramic blocks. The pre-sintered blocks were characterized and indicated 80% of relative density. X-ray diffraction (XRD) only showed MgAl2O4 phase. Samples with 15 x 15 x 1 mm were submitted to infiltration using glass rich in lanthanum (La). The products were characterized by scanning electron microscopy (SEM) and mechanical properties, as hardness and fracture toughness. Results were compared to the commercial product VITA-InCeram Spinell. Relative densities exceeding 92%, hardness around 900 HV and high toughness 2.5 MPa.m1/2 were obtained for both examined systems.
14
Allen, Jan L., Bria A. Crear, Rishav Choudhury, Michael J. Wang, Dat T. Tran, Lin Ma, Philip M. Piccoli, Jeff Sakamoto, and Jeff Wolfenstine. "Fast Li-Ion Conduction in Spinel-Structured Solids." Molecules 26, no. 9 (April 30, 2021): 2625. http://dx.doi.org/10.3390/molecules26092625.
Анотація:
Spinel-structured solids were studied to understand if fast Li+ ion conduction can be achieved with Li occupying multiple crystallographic sites of the structure to form a “Li-stuffed” spinel, and if the concept is applicable to prepare a high mixed electronic-ionic conductive, electrochemically active solid solution of the Li+ stuffed spinel with spinel-structured Li-ion battery electrodes. This could enable a single-phase fully solid electrode eliminating multi-phase interface incompatibility and impedance commonly observed in multi-phase solid electrolyte–cathode composites. Materials of composition Li1.25M(III)0.25TiO4, M(III) = Cr or Al were prepared through solid-state methods. The room-temperature bulk Li+-ion conductivity is 1.63 × 10−4 S cm−1 for the composition Li1.25Cr0.25Ti1.5O4. Addition of Li3BO3 (LBO) increases ionic and electronic conductivity reaching a bulk Li+ ion conductivity averaging 6.8 × 10−4 S cm−1, a total Li-ion conductivity averaging 4.2 × 10−4 S cm−1, and electronic conductivity averaging 3.8 × 10−4 S cm−1 for the composition Li1.25Cr0.25Ti1.5O4 with 1 wt. % LBO. An electrochemically active solid solution of Li1.25Cr0.25Mn1.5O4 and LiNi0.5Mn1.5O4 was prepared. This work proves that Li-stuffed spinels can achieve fast Li-ion conduction and that the concept is potentially useful to enable a single-phase fully solid electrode without interphase impedance.
15
Mombelli, Davide, Silvia Barella, Andrea Gruttadauria, Carlo Mapelli, Gwenn Le Saout, and Eric Garcia-Diaz. "Effects of Basicity and Mesh on Cr Leaching of EAF Carbon Steel Slag." Applied Sciences 9, no. 1 (December 31, 2018): 121. http://dx.doi.org/10.3390/app9010121.
Анотація:
The slag’s chromium leaching is one of the most pressing concerns in Electric Arc Furnace (EAF) carbon and stainless steels production. In recent years, many studies have aimed at understanding which properties (basicity, cooling speed) and phases (spinels, wustite, silicates) determine the Cr leaching, defining different indices (sp-factor, cs-factor) in order to forecast the slag’s behavior compared to the leaching of this toxic metal. The literature suggests that spinel formation is usually a good way to fix Cr and prevent its leaching. However, in some conditions (high basicity, low amount of spinel-forming species) soluble Cr-bearing phases can be formed, i.e., Ca-chromite or unstable spinel. In these conditions, Cr can be leached easily, even if it is bound in a spinel structure. In this paper, the effects of basicity and impurities (Ca, Si) on the instability of Cr-spinel was investigated, with respect to slag mesh. The influence of basicity was also studied on Mg-wustite stability, which might contribute to the leaching of Cr. Different samples of carbon steel slag, suspected of forming unstable spinels, belonging to different steel grade production, were also investigated. Both granulated (4 mm) and milled (<100 μm) slag were analyzed. Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy (SEM-EDS) analyses were carried out to measure the local chemical composition of Cr-bearing phases. This data was correlated with slag basicity (by X-Ray Fluorescence: XRF), spinel fraction (by X-Ray Diffraction: XRD), and Cr leaching (by Inductively Coupled Plasma Mass Spectrometry: ICP-MS). The main results indicate that the increase of the slag basicity implies an increase of the impurity content (Ca, Si) in the spinel, also over-saturated by Cr. This aspect, coupled with spinel geometrical features, seems to justify the unexpected Cr leaching of some slag samples. Basicity does not influence the chemistry of wustite, thus excluding it as an additional Cr leaching source.
16
Nugumanova, Yazgul, Anna Doroshkevich, Ilya Prokopyev, and Anastasiya Starikova. "Compositional Variations of Spinels from Ultramafic Lamprophyres of the Chadobets Complex (Siberian Craton, Russia)." Minerals 11, no. 5 (April 26, 2021): 456. http://dx.doi.org/10.3390/min11050456.
Анотація:
Ultramafic lamprophyres (UMLs) are mantle rocks that provide important information about the composition of specific carbonate–silicate alkaline melts in the mantle as well as the processes contributing to their origin. Minerals of the spinel group typically occur in UMLs and have a unique “genetic memory.” Investigations of the spinel minerals from the UMLs of the Chadobets complex show the physicochemical and thermodynamic features of the alkaline rocks’ crystallization. The spinels of these UMLs have four stages of crystallization. The first spinel xenocrysts were found only in damtjernite pipes, formed from mantle peridotite, and were captured during the rising of the primary melt to the surface. The next stages of the spinel composition evolution are related to the high-chromium spinel crystallization, which changed to a high-alumina composition. The composition then changed to magnesian ulvöspinel–magnetites with strong decreases in the Al and Cr amounts caused by the release of carbon dioxide, rapid temperature changes, and crystallization of the main primary groundmass minerals such as phlogopite and carbonates. Melt inclusion analyses showed the predominance of aluminosilicate (phlogopite, clinopyroxene, and/or albite) and carbonate (calcite and dolomite) daughter phases in the inclusions that are consistent with the chemical evolution of the Cr-spinel trend. The further evolution of the spinels from magnesian ulvöspinel–magnetite to Ti-magnetite is accompanied by the formation of atoll structures caused by resorption of the spinel minerals.
17
Anderson, Ian M., M. Grant Norton, and C. Barry Carter. "TEM study of thin iron oxide films deposited by pulsed-laser ablation." Proceedings, annual meeting, Electron Microscopy Society of America 49 (August 1991): 780–81. http://dx.doi.org/10.1017/s042482010008821x.
Анотація:
Iron-oxide-based compounds are of technological interest because of their unique magnetic properties. Thin films of these compounds are especially suited to applications such as magnetic recording devices. The binary Fe-O system provides a model for the study of iron-oxide-based compounds, since the multiple valence of the Fe cations permits the formation of phases having a variety of crystal structures. These structures include rock salt (wüstite, Fe1-δO), two spinels (magnetite, Fe3O4 and maghemite, γ-Fe2O3), and corundum (hematite, α-Fe2O3). The former three phases have cubic-close-packed oxygen sublattices, while the latter has a hexagonal-close-packed oxygen sublattice. The γ-Fe2O3 phase is a metastable, cation-deficient spinel, generally formed by careful low-temperature oxidation of the magnetite phase.Thin iron oxide films have been deposited by pulsed-laser ablation onto (001)-oriented MgO single-crystal substrates. The microstructure and epitaxy of these films have been studied using transmission electron microscopy (TEM) and selected-area diffraction (SAD).
18
Zhou, Mei-Fu, Reid R. Keays, Peter C. Lightfoot, Gordon G. Morrison, and Michelle L. Moore. "Petrogenetic significance of chromian spinels from the Sudbury Ignecus Complex, Ontario, Canada." Canadian Journal of Earth Sciences 34, no. 10 (October 1, 1997): 1405–19. http://dx.doi.org/10.1139/e17-113.
Анотація:
Chromian spinels occur in mafic–ultramafic inclusions in the Sublayer of the Sudbury Igneous Complex (SIC) as well as in mafic–ultramafic rocks in the immediate footwall of the Sublayer. The host rocks are pyroxenite and melanorite with minor dunite, harzburgite, and melatroctolite. As common accessory phases in these rocks, the chromian spinels display euhedral or subhedral forms and are included in olivine and orthopyroxene. Chromian spinel grains generally have ilmenite lamellae and contain abundant inclusions (zircon, olivine, diopside, plagioclase, biotite, and sulfide). All the chromian spinels have similar trace element abundances and are rich in TiO2 (0.5–15 wt.%). They have constant Cr# (100Cr/(Cr + Al)) (55–70) and exhibit a continuum in composition that traverses the normal fields of spinels in a Al–(Fe3+ + 2Ti)–Cr triangular diagram. This continuum extends to that of the composition of chromian magnetite in the host norite matrix to the mafic–ultramafic inclusions. This continuum in composition of the spinels suggests that the noritic matrix to the Sublayer formed from the same magma as the inclusions. A positive correlation between the Cr and Al contents of the spinels was probably produced by dilution of these elements by Fe3+ contributed, perhaps, by a plagioclase-saturated melt. Zircon inclusions in a chromian spinel grain reflect incorporation of crustal, felsic materials into the magma before crystallization of chromian spinel. The chemical characteristics and mineral inclusions of the spinels suggest that the Sublayer formed in response to magma mixing. It is suggested that subsequent to the formation of the crustal melt, mantle-derived high-Mg magmas mixed vigourously with this and generated the magmatic sulfides that eventually formed the Ni – Cu – platinum-group elements sulfide ore deposits. Some of the early crystallization products of the high-Mg magma settled to the chamber floor, where they partially mixed with the crustal melt and formed the mafic–ultramafic inclusions and footwall complexes.
19
Liu, Liping, Xi Liu, Xinjian Bao, Qiang He, Wei Yan, Yunlu Ma, Mingyue He, Renbiao Tao, and Ruqiang Zou. "Si-Disordering in MgAl2O4-Spinel under High P-T Conditions, with Implications for Si-Mg Disorder in Mg2SiO4-Ringwoodite." Minerals 8, no. 5 (May 12, 2018): 210. http://dx.doi.org/10.3390/min8050210.
Анотація:
A series of Si-bearing MgAl2O4-spinels were synthesized at 1500–1650 °C and 3–6 GPa. These spinels had SiO2 contents of up to ~1.03 wt % and showed a substitution mechanism of Si4+ + Mg2+ = 2Al3+. Unpolarized Raman spectra were collected from polished single grains, and displayed a set of well-defined Raman peaks at ~610, 823, 856 and 968 cm−1 that had not been observed before. Aided by the Raman features of natural Si-free MgAl2O4-spinel, synthetic Si-free MgAl2O4-spinel, natural low quartz, synthetic coesite, synthetic stishovite and synthetic forsterite, we infer that these Raman peaks should belong to the SiO4 groups. The relations between the Raman intensities and SiO2 contents of the Si-bearing MgAl2O4-spinels suggest that under some P-T conditions, some Si must adopt the M-site. Unlike the SiO4 groups with very intense Raman signals, the SiO6 groups are largely Raman-inactive. We further found that the Si cations primarily appear on the T-site at P-T conditions ≤~3–4 GPa and 1500 °C, but attain a random distribution between the T-site and M-site at P-T conditions ≥~5–6 GPa and 1630–1650 °C. This Si-disordering process observed for the Si-bearing MgAl2O4-spinels suggests that similar Si-disordering might happen to the (Mg,Fe)2SiO4-spinels (ringwoodite), the major phase in the lower part of the mantle transition zone of the Earth and the benchmark mineral for the very strong shock stage experienced by extraterrestrial materials. The likely consequences have been explored.
20
Dolníček, Zdeněk, Michaela Krejčí Kotlánová, and Rostislav Koutňák. "Vliv diagenetických procesů na asociaci těžkých minerálů v pískovcích z lokality Slivotín (ždánická jednotka, flyšové pásmo Vnějších Západních Karpat, Česká republika)." Bulletin Mineralogie Petrologie 29, no. 1 (2021): 27–40. http://dx.doi.org/10.46861/bmp.29.027.
Анотація:
An electron microprobe study of polished sections prepared from a sample of fine-grained sandstone from the locality Slivotín (Ždánice-Hustopeče Formation, Ždánice Unit, Flysch Belt of the Outer Western Carpathians, Czech Republic) allowed to yield in addition to data on chemical composition also the detailed information on in situ textural relationships of individual minerals. During our study, emphasis was given to accessory phases belonging to the translucent heavy mineral fraction. The detrital garnet (Alm36-82Grs2-45Prp2-22Sps0-15) was extensively dissolved and replaced by calcite cement from its margins and along the cracks. Detrital fluorapatite was dissolved in a similar way, however, dissolution episode was followed by growth of authigenic rims composed of carbonate-fluorapatite. Other observed heavy minerals (zircon, chrome spinel, TiO2 phase, monazite, tourmaline) probably remained unaltered by diagenetic processes. The chemical composition of chrome spinels varies mostly between magnesiochromite and chromite, whereas spinel is very rare. The chemical composition of garnets and chrome spinels is comparable with published data from Czech, Polish and Slovak parts of the Flysch Belt of the Western Carpathians, and indicates the primary source of detrital material in rocks of deeper parts of orogen, characterized especially by the presence of catazonal metamorphites and almost lacking volcanic rocks. Redeposition of heavy minerals from older sediments cannot also be ruled out. The pronounced diagenetic alteration of garnet, if not very scarce in the area of Flysch Belt, could help to explain the earlier observations of wide fluctuations of contents of garnet in heavy mineral concentrates.
21
Cao, Long-hu, Cheng-jun Liu, Qing Zhao, and Mao-fa Jiang. "Analysis on the stability of chromium in mineral phases in stainless steel slag." Metallurgical Research & Technology 115, no. 1 (November 28, 2017): 114. http://dx.doi.org/10.1051/metal/2017071.
Анотація:
Stainless steel slag from high alloy steel is hardly used in the construction industry. The chromium leaching in unstable phase is the limiting factor for the application in the slag. The aim of this study is to investigate the stability of mineral phases in stainless steel slag. In this work, the mineral phases were firstly confirmed through experimental results by SEM-EDS and XRD. Thermodynamic calculation and leaching test were adopted to characterize the theoretical stability of mineral phases in aqueous solution. The results showed that the main phases in the stainless steel slag were spinel, melilite [solid solution of gehlenite (Ca2Al2SiO7) and akermanite (Ca2MgSi2O7)], dicalcium silicate, merwinite and periclase phases. It can be concluded that the minerals behave differently when dissolving in aqueous solution and the dissolution of dicalcium silicate (Ca2SiO4), merwinite (Ca3MgSi2O8), akermanite (Ca2MgSi2O7) and periclase phase could be generally higher, especially at lower pH values. In addition, the solubility of chromium in the spinel phase is considered low. The leaching test demonstrated that the formation of spinel phase can limit the leaching of chromium and the chromium existing in the silicate and periclase phases can facilitate the chromium leaching.
22
Uenver-Thiele, Laura, Alan B. Woodland, Tiziana Boffa Ballaran, Nobuyoshi Miyajima, and Dan J. Frost. "Phase relations of Fe-Mg spinels including new high-pressure post-spinel phases and implications for natural samples." American Mineralogist 102, no. 10 (October 2017): 2054–64. http://dx.doi.org/10.2138/am-2017-6119.
23
Fan, Helin, Huamei Duan, Wenjie He, Dengfu Chen, Tao Liu, Mujun Long, and Pei Xu. "Sequential extraction of vanadium and chromium from chromium-bearing vanadium slag through two-stage soda roasting-water leaching." Metallurgical Research & Technology 115, no. 6 (2018): 607. http://dx.doi.org/10.1051/metal/2018093.
Анотація:
The sequential extraction of vanadium and chromium from the chromium-bearing vanadium slag through two-stage soda roasting-water leaching was proposed. The precipitation order and thermodynamic stability of Cr-spinel and V-spinel were thoroughly calculated with FactSage 6.3 software. The mechanism of the sequential extraction process is further determined by X-ray diffraction (XRD). Thermodynamic calculations show that the precipitation order of main phases in the chromium-bearing vanadium slag is as follows: Cr-spinel → V-spinel → Fe-olivine, while the priority of the reaction between main phases with Na2CO3 follows the order of Fe-olivine → V-spinel → Cr-spinel. XRD results reveal that the vanadium-bearing phase in roasted slag is water-soluble NaVO3, while the chromium-bearing phase in roasted slag is Cr-spinel ((Mn, Fe) Cr2O4) and solid solutions ((Fe0.6Cr0.4)2 O3) with the soda amount of 21% and temperature of 800 °C. The different evolution route of vanadium-bearing phase and chromium-bearing phase during the roasting process ensures preferential extraction of vanadium from the chromium-bearing vanadium slag. The leaching rates of vanadium and chromium reach 89.36% and 4.91% with optimized experimental conditions. The high leaching rate of vanadium and low leaching rate of chromium show good results of preferential extraction of vanadium from the chromium-bearing vanadium slag.
24
Borysenko, Oksana, Sergey Logvinkov, Galina Shabanova, Alla Korohodska, Marina Ivashura, and Andrii Ivashura. "SUBSOLIDUS STRUCTURE OF THE MgO – FeO – Al2O3 SYSTEM." Bulletin of the National Technical University «KhPI» Series: New solutions in modern technologies, no. 1(7) (April 23, 2021): 59–64. http://dx.doi.org/10.20998/2413-4295.2021.01.09.
Анотація:
Three-component systems constitute the physicochemical basis of most refractory materials and the analysis of their subsolidus structure makes it possible to accurately predict the areas of compositions with optimal properties, as well as give recommendations on the technological parameters of production, sintering, and operation of the materials obtained. As a result of the carried out thermodynamic analysis of the MgO – FeO – Al2O3 system, it was found that the partition of the system into elementary triangles undergoes changes in two temperature ranges: I – up to a temperature of 1141 K and II – above a temperature of 1141 K. By calculation methods, the geometrical-topological characteristics of the subsolidus structure of the system are determined MgO – FeO – Al2O3: areas of elementary triangles, degree of their asymmetry, area of regions in which phases exist, probability of phase existence in the system. It has been established that, over the entire temperature range, there is a fairly extended concentration region of spinel phases: hercynite (FeAl2O4) – noble spinel (MgAl2O4). Moreover, periclase (MgO) coexists simultaneously with both spinels only in the low-temperature region. This indicates that when obtaining periclase-spinel refractories with increased heat resistance, an important technological parameter is a cooling rate below 1141 K. To obtain periclase-spinel refractories with branched microcracking of the structure due to differences in the thermal expansion coefficients of periclase, hercynite and noble spinel, the most rational concentration region of the system under study is which is common for two elementary triangles (MgO – FeAl2O4 – MgAl2O4 and MgO – FeO – MgAl2O4) existing in different temperature ranges. At high firing temperatures, the elementary triangle MgO – FeO – MgAl2O4 has a maximum area and a minimum degree of asymmetry, and upon cooling, MgO – FeAl2O4 – MgAl2O4 is formed, which is quite large in area, but has a high degree of asymmetry. Therefore, the composition of the charge for periclase-spinel refractories should be predicted with a high dosage accuracy and with a significant homogenization time of the components during mixing, since the concentration region common for both of the above elementary triangles is significantly reduced. Thus, the division of the MgO – FeO – Al2O3 system into elementary triangles and the analysis of the geometrical-topological characteristics of the phases of the system made it possible to select in the system under study the range of compositions with optimal properties for obtaining spinel-containing materials.
25
Zhang, Tao, Wang Zhou, Yuanyuan Li, Qian Ye, Xiaowen Yu, and Zhao Chen. "Effect of CaO on the Phase Evolution of Vanadium Slag during Crystallization and Roasting–Leaching Processes for Selective Extraction of Vanadium." Crystals 12, no. 7 (June 30, 2022): 927. http://dx.doi.org/10.3390/cryst12070927.
Анотація:
In this paper, the effects of CaO on the phase evolution mechanism of vanadium slag during slagging, direct roasting, and (NH4)2CO3 leaching processes are investigated. Results indicate that with the increase in CaO content, vanadium is always concentrated as (Fe, Mn, Mg)V2O4 in spinels, part of titanium is concentrated and transformed into CaTiO3, and phosphorus is concentrated in 3CaO·P2O5 (C3P) and transformed into n·2CaO·SiO2-3CaO·P2O5 (nC2S-C3P). During the direct roasting process, a part of the vanadium-containing spinel phase oxidizes and reacts with Ca2SiO4 to produce calcium vanadate (Ca3V2O8, Ca10V6O25, and Ca2V2O7), which is soluble in (NH4)2CO3 aqueous solution. However, a part of the vanadium-containing spinel phase is oxidized and decomposed to vanadium oxides (V2O5 and V6O13), which are insoluble in (NH4)2CO3 aqueous solution. This is not beneficial for vanadium extraction using (NH4)2CO3 aqueous solution. In addition, (NH4)2CO3 aqueous solution can restrain the leaching of C3P from the nC2S-C3P solid solution in the directly roasted vanadium slag with high CaO content.
26
Grazenaite, Egle, Edita Garskaite, Zivile Stankeviciute, Eva Raudonyte-Svirbutaviciene, Aleksej Zarkov, and Aivaras Kareiva. "Ga-Substituted Cobalt-Chromium Spinels as Ceramic Pigments Produced by Sol–Gel Synthesis." Crystals 10, no. 12 (November 25, 2020): 1078. http://dx.doi.org/10.3390/cryst10121078.
Анотація:
For the first time to the best of our knowledge, cobalt-chromium spinels CoCr2−xGaxO4 with different amounts of gallium (x = 0–2 with a step of 0.5) were synthesized via the aqueous sol–gel route as ceramic pigments. The phase composition, crystallite size, morphological features, and color parameters of new compositions and their corresponding ceramic glazes were investigated using XRD, CIELab, SEM, and optical microscopy. It was demonstrated that the formation of single-phase CoCr2−xGaxO4 samples was problematic. Full substitution of Cr3+ by Ga3+ ion in the spinel resulted in the formation of light blue powders, which yielded violetish blue color for the corresponding ceramic glaze.
27
Mi, Zhongying, Weiguang Shi, Lifei Zhang, Sean Shieh, and Xi Liu. "Equation of State of a Natural Chromian Spinel at Ambient Temperature." Minerals 8, no. 12 (December 13, 2018): 591. http://dx.doi.org/10.3390/min8120591.
Анотація:
A natural chromian spinel with the composition (Mg0.48(3)Fe0.52(3))(Fe0.06(1)Al0.28(1)Cr0.66(2))2O4 was investigated up to 15 GPa via synchrotron X-ray diffraction with a diamond-anvil cell at room temperature. No phase transition was clearly observed up to the maximum experimental pressure. The pressure–volume data fitted to the third-order Birch–Murnaghan equation of state yielded an isothermal bulk modulus ( K T 0 ) of 207(5) GPa and its first pressure derivative ( K T 0 ′ ) of 3.2(7), or K T 0 = 202(2) GPa with K T 0 ′ fixed as 4. With this new experimental result and the results on some natural chromian spinels in the literature, a simple algorithm describing the relation between the K T 0 and the compositions of the natural chromian spinels was proposed. To examine this algorithm further, more compression experiments should be performed on natural chromian spinels with different chemical compositions.
28
Zhao, B., P. Hayes, and E. Jak. "Effects of CaO, Al2O3 and MgO on liquidus temperatures of copper smelting and converting slags under controlled oxygen partial pressures." Journal of Mining and Metallurgy, Section B: Metallurgy 49, no. 2 (2013): 153–59. http://dx.doi.org/10.2298/jmmb120812009z.
Анотація:
Phase equilibria of silicate slags relevant to the copper smelting/converting operations have been experimentally studied over a wide range of slag compositions, temperatures and atmospheric conditions. Selected systems are of industrial interest and fill the gaps in fundamental information required to systematically characterise and describe copper slag chemistry. The experimental procedures include equilibration of synthetic slag at high temperatures, rapid quenching of resulting phases, and accurate measurement of phase compositions using electron probe X-ray microanalysis (EPMA). The effects of CaO, Al2O3 and MgO on the phase equilibria of this slag system have been experimentally investigated in the temperature range 1200 to 1300 oC and oxygen partial pressures between 10-5 and 10-9 atm. It was found that spinel and silica are major primary phases in the composition range related to copper smelting/converting slags. In addition, olivine, diopside and pyroxene also appear at certain conditions. The presence of CaO, MgO and Al2O3 in the slag increases the spinel liquidus and decreases the silica liquidus. Liquidus temperatures in silica primary phase field are not sensitive to Po2; Liquidus temperatures in spinel primary phase field increase with increasing Po2. At 1300 oC and low Po2, the spinel (Fe2+,Mg2+)O.(Al3+,Fe3+) primary phase field can be replaced by wustite (Fe2+,Mg2+)O.
29
Wang, N., M. Chen, Z. Zou, Z. Zhang, Y. Xiao, and Y. Yang. "Liquidus and phase equilibria in CaO-Al2O3-FeOx-SiO2 system under intermediate oxygen partial pressure." Journal of Mining and Metallurgy, Section B: Metallurgy 49, no. 2 (2013): 139–44. http://dx.doi.org/10.2298/jmmb120826014w.
Анотація:
Phase equilibria of silicate slags relevant to the copper smelting/converting operations have been experimentally studied over a wide range of slag compositions, temperatures and atmospheric conditions. Selected systems are of industrial interest and fill the gaps in fundamental information required to systematically characterise and describe copper slag chemistry. The experimental procedures include equilibration of synthetic slag at high temperatures, rapid quenching of resulting phases, and accurate measurement of phase compositions using electron probe X-ray microanalysis (EPMA). The effects of CaO, Al2O3 and MgO on the phase equilibria of this slag system have been experimentally investigated in the temperature range 1200 to 1300 oC and oxygen partial pressures between 10-5 and 10-9 atm. It was found that spinel and silica are major primary phases in the composition range related to copper smelting/converting slags. In addition, olivine, diopside and pyroxene also appear at certain conditions. The presence of CaO, MgO and Al2O3 in the slag increases the spinel liquidus and decreases the silica liquidus. Liquidus temperatures in silica primary phase field are not sensitive to Po2; Liquidus temperatures in spinel primary phase field increase with increasing Po2. At 1300?C and low Po2, the spinel (Fe2+,Mg2+)O.(Al3+,Fe3+) primary phase field can be replaced by wustite (Fe2+,Mg2+)O.
30
De Villiers, Johan PR, Delphin Mulange, and Andrie Mariana Garbers-Craig. "The Effect of Titanium Oxide Additions on the Phase Chemistry and Properties of Chromite-Magnesia Refractories." Ceramics 3, no. 1 (March 20, 2020): 127–43. http://dx.doi.org/10.3390/ceramics3010013.
Анотація:
The microstructure of a direct-bonded chromite-magnesia refractory brick, typically used in copper and platinum converters, was modified by adding different amounts of nano-size TiO2 to the raw material mixture. Bricks with 0, 1, 3, 5, and 7 mass% TiO2 were produced and compared in terms of spinel formation; the role of the tetravalent cation Ti4+ in the bonding phase; as well as changes in density, porosity, thermal expansion, and internal stress. This was done through a comprehensive XRD and SEM-EDS study. It was found that Ti is accommodated in the secondary spinel that has formed, where Mg in excess of unity in the tetrahedral site combines with an equal amount of Ti in the octahedral sites to maintain charge balance. The 1 mass% TiO2 brick had the lowest bulk density (but not significantly different from the original chromite-magnesia brick), the smallest difference in unit cell volumes between the primary and secondary spinels, and the lowest stress arising from the smallest difference in linear thermal expansion coefficients of the phases present. The calculated porosities correspond well with experimentally determined apparent porosity values, whereas the linear thermal expansion coefficients calculated at 1392K are similar to the values measured from 293 to 1273 K.
31
Ferreira, Pedro Paulo Linhares, Dulce Maria de Araújo Melo, Rodolfo Luiz Bezerra de Araújo Medeiros, Tomaz Rodrigues de Araújo, Fernando Velcic Maziviero, and Ângelo Anderson Silva de Oliveira. "Green synthesis with Aloe Vera of MgAl2O4 substituted by Mn and without calcination treatment." Research, Society and Development 11, no. 6 (April 23, 2022): e14411628873. http://dx.doi.org/10.33448/rsd-v11i6.28873.
Анотація:
Magnesium aluminates (MgAl2O4) with Mn substituting sites A and B were synthesized by the microwave-assisted combustion method applying high power (900 W) using Aloe Vera as a green chelating agent. The study evaluated the effect of the presence of Aloe Vera and the subsequent heat treatment on the structural characteristics of spinel powders by X-ray diffraction (XRD). The effect of heat treatment was evaluated in two ways: with and without calcination. The results showed that the substitutes occurred forming the following phases: Mg0.21Mn2.36Al0.43O4, Mg0.13Mn2.63Al0.25O4, Mg0.31Mn2.06Al0.63O4 substituting site A; and MgMn1.88Al0.13O4 and MgMn1.75Al0.25O4 substituting site B. The presence of Mn and Aloe Vera ions affected the spinel crystal structure. The crystallinity degree is less intense when the magnesium aluminate was substituted by the Mn ion due to the amount of deformations in the crystal system induced by the substituent ion. However, the calcination of the powders increased the crystallinity degree in all scenarios. Furthermore, the substitution caused alteration in the lattice parameters due to the difference between the ionic radius of the substituent and the Mg2+ or Al3+ ion evidenced in the positions of 2θ. The spinel cubic phase was found in most materials, although the tetrahedral phase was observed in some Mn-substituted structures. The crystallite sizes of the powders were influenced by the presence of phytochemicals present in Aloe Vera. A decrease in crystallite size was observed when the materials were calcined as a result of the gasification of biomolecules from the plant extract. However, these biomolecules help in dissociating precursors, albeit slowly, which prevented crystallite growth. The use of Aloe Vera as a chelating agent proved to be efficient in the synthesis of magnesium aluminate spinels, pointing out the synthesized material as a promising route for the green synthesis field.
32
Massarotti, V., M. Bini, and D. Capsoni. "Structural and Defect Study of LiMn2O4 Formation." Zeitschrift für Naturforschung A 51, no. 4 (April 1, 1996): 267–76. http://dx.doi.org/10.1515/zna-1996-0406.
Анотація:
Abstract The LiMn2O4 formation from MnO and Li2CO3 mixtures with lithium cationic fraction 0.31 <̲ x <̲ 0.40 was studied by structural profile refinement from X-ray data, thermal (TGA and DSC) measurements and scanning electron microscopy (SEM) observations. Quantitative phase analysis, structural and microstructural parameters and composition of the coexisting phases were obtained. Different behaviours were observed in the composition ranges 0.33 <̲ x <̲ 0.35 and x >̲ 0.37. In the former range only the stoichiometric spinel phase was obtained, in the latter, in addition to the Li2MnO3 compound, two spinel phases could be considered: I) LiMn2O4 stoichiometric spinel; II) Li1 + yMn2-yO4 (0.11 <̲ y <̲ 0.23), a non-stoichiometric phase whose small particle size resulted practically independent of the initial composition and annealing temperature. Such a conclusion was supported also by SEM observations. The relative abundance of phase II increased with increasing lithium content and with decreasing temperature.
33
Kurajica, Stanislav, Emilija Tkalčec, Vilko Mandić, Iva Lozić, and Jörg Schmauch. "Sol-Gel Derived Mullite-Gahnite Composite." Advances in Science and Technology 87 (October 2014): 126–31. http://dx.doi.org/10.4028/www.scientific.net/ast.87.126.
Анотація:
Mullite-gahnite composites with different phase-proportions were prepared using sol-gel process. Crystallization path was determined using differential thermal analysis (DTA). X-ray powder diffraction (XRD) was used to study the crystal phases development. The course of the thermal reactions is dominated by the intermediate formation of two spinel phases. The former phase was attributed to gahnite, while the latter to Al-Si spinel. Zn loading decreases amounts of mullite and α-alumina, while increases gahnite and amorphous phase. The observed microstructure of sintered bodies is characterized by fine gahnite particles distributed among larger mullite grains, which is highly favourable for ceramics with high mechanical requirements.
34
Tabary, P., C. Servant та M. Guymont. "High-resolution transmission electron microscopy study of the φ′- and δ-AlON spinel phases of the pseudo-binary section AlN–Al2O3". Journal of Applied Crystallography 32, № 4 (1 серпня 1999): 755–60. http://dx.doi.org/10.1107/s0021889899005221.
Анотація:
A previously proposed structural model [Tabary & Servant (1999).J. Appl. Cryst.32, 253–272] for the φ′- and δ-AlON spinel phases, which allows for the double modulation of composition and displacement of cations and anions and which describes both phases and their relationships to the γ-AlON spinel phase, is here supported by high-resolution electron microscopy observations.
35
Pekov, Igor, Fedor Sandalov, Natalia Koshlyakova, Marina Vigasina, Yury Polekhovsky, Sergey Britvin, Evgeny Sidorov, and Anna Turchkova. "Copper in Natural Oxide Spinels: The New Mineral Thermaerogenite CuAl2O4, Cuprospinel and Cu-Enriched Varieties of Other Spinel-Group Members from Fumaroles of the Tolbachik Volcano, Kamchatka, Russia." Minerals 8, no. 11 (November 1, 2018): 498. http://dx.doi.org/10.3390/min8110498.
Анотація:
This paper is the first description of natural copper-rich oxide spinels. They were found in deposits of oxidizing-type fumaroles related to the Tolbachik volcano, Kamchatka, Russia. This mineralization is represented by nine species with the following maximum contents of CuO (wt.%, given in parentheses): a new mineral thermaerogenite, ideally CuAl2O4 (26.9), cuprospinel, ideally CuFe3+2O4 (28.6), gahnite (21.4), magnesioferrite (14.7), spinel (10.9), magnesiochromite (9.0), franklinite (7.9), chromite (5.9), and zincochromite (4.8). Cuprospinel, formerly known only as a phase of anthropogenic origin, turned out to be the Cu-richest natural spinel-type oxide [sample with the composition (Cu0.831Zn0.100Mg0.043Ni0.022)Σ0.996(Fe3+1.725Al0.219Mn3+0.048Ti0.008)Σ2.000O4 from Tolbachik]. Aluminum and Fe3+-dominant spinels (thermaerogenite, gahnite, spinel, cuprospinel, franklinite, and magnesioferrite) were deposited directly from hot gas as volcanic sublimates. The most probable temperature interval of their crystallization is 600–800 °C. They are associated with each other and with tenorite, hematite, orthoclase, fluorophlogopite, langbeinite, calciolangbeinite, aphthitalite, anhydrite, fluoborite, sylvite, halite, pseudobrookite, urusovite, johillerite, ericlaxmanite, tilasite, etc. Cu-bearing spinels are among the latest minerals of this assemblage: they occur in cavities and overgrow even alkaline sulfates. Cu-enriched varieties of chrome-spinels (magnesiochromite, chromite, and zincochromite) were likely formed in the course of the metasomatic replacement of a magmatic chrome-spinel in micro-xenoliths of ultrabasic rock under the influence of volcanic gases. The new mineral thermaerogenite, ideally CuAl2O4, was found in the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption. It forms octahedral crystals up to 0.02 mm typically combined in open-work clusters up to 1 mm across. Thermaerogenite is semitransparent to transparent, with a strong vitreous lustre. Its colour is brown, yellow-brown, red-brown, brown-yellow or brown-red. The mineral is brittle, with the conchoidal fracture, cleavage is none observed. D(calc.) is 4.87 g/cm3. The chemical composition of the holotype (wt.%, electron microprobe) is: CuO 25.01, ZnO 17.45, Al2O3 39.43, Cr2O3 0.27, Fe2O3 17.96, total 100.12 wt.%. The empirical formula calculated on the basis of 4 O apfu is: (Cu0.619Zn0.422)Σ1.041(Al1.523Fe3+0.443Cr0.007)Σ1.973O4. The mineral is cubic, Fd-3m, a = 8.093(9) Å, V = 530.1(10) Å3. Thermaerogenite forms a continuous isomorphous series with gahnite. The strongest lines of the powder X-ray diffraction pattern of thermaerogenite [d, Å (I, %) (hkl)] are: 2.873 (65) (220), 2.451 (100) (311), 2.033 (10) (400), 1.660 (16) (422), 1.565 (28) (511) and 1.438 (30) (440).
36
Lenaz, D., M. Velicogna, U. Hålenius, and B. O'Driscoll. "Structural parameters of Cr-bearing spinels and pleonaste from the Cuillin Igneous Complex (Isle of Skye, Scotland): Implications for metamorphic and cooling history." Mineralogical Magazine 80, no. 5 (August 2016): 749–63. http://dx.doi.org/10.1180/minmag.2016.080.021.
Анотація:
AbstractThe Outer Layered Suite of the Cuillin Igneous Complex (Isle of Skye, NW Scotland) comprises a Peridotite Series and a younger Allivalite Series (the latter comprising troctolites, eucrites and gabbros). Close to the junction between the Peridotite and the Allivalite Series (but wholly contained within the latter), an ultramafic breccia unit containing abundant peridotite xenoliths crops out. In the Peridotite Series, reddish-brown Cr-bearing spinels are present as disseminated crystals in the peridotite and also as chromitite seams, while in the peridotite xenoliths of the breccia unit, green pleonaste occurs in both of these modes of textural occurrence. Optical absorption spectroscopy reveals that the colour difference between the two spinel phases is related mainly to variable Al, Cr and Fe contents, while crystal structural analysis shows that the cooling rate calculated utilizing the oxygen positional parameter is comparable for all samples. The intracrystalline closure temperature for the Cr-spinel in the Peridotite Series is different for the disseminated and seam textural occurrences of the spinels, while the temperatures yielded by pleonaste in the peridotite xenoliths are the same for both textural occurrences. Our dataset suggests that the pleonaste in the peridotite xenoliths has been heated and equilibrated under subsolidus conditions, probably during breccia formation. During this heating, homogenization of the closure temperatures of pleonaste spinels occurred.
37
Sherendo, Tatyana, Valentin Mitrofanov, Aleksey Vdovin, Petr Martyshko, Aleksey Alexeev, Dmitry Zamyatin, Vladimir Vazhenin, and Lidia Pamyatnykh. "Magnetic Clusters in Natural Ferro-Chromian Spinels." Solid State Phenomena 233-234 (July 2015): 587–90. http://dx.doi.org/10.4028/www.scientific.net/ssp.233-234.587.
Анотація:
The results of investigations of natural iron-chromium spinels of variable composition Fe2+(Cr2-xFex3+)O4 of the chromite-bearing Klyuchevskoi massif (Middle Urals), which are the main carriers of the magnetization of rocks are presented. Substantial changes in the composition and in magnetic structure of accessory chrome-spinels scattered in the host rock are established, unlike the almost unaltered ore-forming chrome-spinels, under the influence of secondary geological processes. To establish the connection between the chrome-spinel changes at the microlevel and features of the geomagnetic field anomalies created by this carrier of magnetization of rocks, it is carried out a complex of investigations of Fe-Cr-spinels (thermomagnetic analysis over the temperature range (4÷1000) K; magnetic resonance (MR) spectroscopy and magnetic force microscopy (MFM) in addition to magnetomineralogical studies). As a result, in the relict areas of grains of the accessory chrome-spinels were first discovered the magnetic clusters (superparamagnetic phases) in the form of single or groups of 2 – 3 magnetic dipoles of tens nanometers in size, or in the form of chain-like structures of magnetic dipoles/single domains.
38
Białas, Anna, Kamil Rugała, Cezary Czosnek, Grzegorz Mordarski, and Jacek Gurgul. "Copper Aluminum Spinels Doped with Cerium as Catalysts for NO Removal." Catalysts 10, no. 12 (November 28, 2020): 1388. http://dx.doi.org/10.3390/catal10121388.
Анотація:
Cu-Ce(Mn)-Al oxide catalysts to NO removal in the broad temperature range were synthesized and tested. The precursor of copper aluminium spinel was obtained with the coprecipitation method. By this method, Cu–Al spinels with various amounts of manganese and cerium were synthesized as well. These oxides crystallized in the structure of inverse spinel; however, Ce doping caused the appearance of additional CeO2 phase as determined by XRD. The samples were mesoporous solids with moderate surface area and porosity measured by low temperature sorption of nitrogen. The addition of another metal to Cu–Al spinel caused an increase of activity in selective catalytic reduction of nitrogen oxide with ammonia. The presence of manganese caused the formation of a higher amount of N2O by-product. The catalytic activity increased with the cerium concentration. For the sample with the atomic ratio Ce0.15Cu0.18, ca. 90% of NO conversion was registered between 200 and 350 °C. As examined with XPS spectroscopy, such conversion was attained due to the good dispersion of copper on the catalyst surface. This copper was placed mainly in spinel octahedral positions which enable its easier reduction. The spinel structure causes the presence of cerium as the trivalent cation important in redox cycles with the participation of copper.
39
Mazurenko, Ju. "Nickel substituted effect of on structural, Mössbauer and dielectric properties of spinel-type lithium ferrites." Physics and Chemistry of Solid State 21, no. 3 (September 30, 2020): 453–61. http://dx.doi.org/10.15330/pcss.21.3.453-461.
Анотація:
Ni-substituted lithium ferrite Li0.5-x/2NixFe2.5-x/2O4, where (х=0.0, 0.2, 0.4, 0.6, 0.8, 1.0) synthesized through sol-gel auto-combustion method was investigated for its structural, Mossbauer, and dielectric properties. At low doses of substitution, two spinels of the same composition coexist in the structure, one of spatial group P4332, so-called spinel with superstructure, in which the iron and lithium ions are arranged along the crystallographic direction <110> and the other is a spatial group Fd3m, random spinel. The presence of both spinels is observed at low content of the doped element (x = 0.2 and 0.4). In case of increase Ni2+ ions, random component disappears and only the ordered phase remains. The particle sizes of the synthesized product are around 22-45 nm. According to the proposed cationic distribution of Nickel ions are localized in the A-site and lithium ions in the B-site. Iron ions are redistributed over both sites at a ratio of about 1:2. It is shown, that the conductive and dielectric properties of the synthesized powders have a frequency dependence characteristic of ferrite materials, the behavior of which is explained based on the hopping mechanism of conductivity and inter-grain polarization.
40
Snyders, C. D., E. E. Ferg, and D. Billing. "An investigation into the temperature phase transitions of synthesized materials with Al- and Mg-doped lithium manganese oxide spinels by in situ powder X-ray diffraction." Powder Diffraction 32, no. 1 (December 23, 2016): 23–30. http://dx.doi.org/10.1017/s088571561600066x.
Анотація:
Three spinel materials were prepared and characterized by in situ powder X-ray diffraction (PXRD) techniques to track their phase changes that occurred in the typical batch synthesis process from a sol–gel mixture to the final crystalline spinel oxide. The materials were also characterized by thermal gravimetric analysis, whereby the materials decomposition mechanisms that were observed as the precursor, was gradually heated to the final oxide. The results showed that all the materials achieved their total weight loss at about 400 °C. The in situ PXRD analysis showed the progression of the phase transitions where certain of the materials changed from a crystalline precursor to an amorphous intermediate phase and finally to the spinel cathode oxide (Li1.03Mg0.2Mn1.77O4). For other materials, the precursor would start as an amorphous phase and upon heating, convert into an impure intermediate phase (Mn2O3) before forming the final spinel oxide (Li1.03Mn1.97O4). On the other hand, the LiAl0.4Mn1.6O4 would start with an amorphous precursor, with no intermediate phases and immediately formed the final spinel oxide phase. The in situ PXRD study also showed the increases in the materials respective lattice parameters of the crystalline unit cells upon heating and the significant increases in their crystallite sizes when heated above 600 °C.
41
Laokul, Paveena, and S. Maensiri. "Synthesis, Characterization and Sintering Behavior of Nanocrystalline Cordierite Ceramics." Advances in Science and Technology 45 (October 2006): 242–47. http://dx.doi.org/10.4028/www.scientific.net/ast.45.242.
Анотація:
Nanocrystalline cordierite powders were prepared by the polymerized complex method. The synthesized precursor was calcined in air at 600-1200 oC for 1h, and the calcined powders were fully characterized by TG/DTA, BET, XRD, SEM, and TEM. The XRD and selected-area electron diffraction (SAED) analysis confirmed the development of the phase composition of cordierite powders showing amorphous phase after calcination at temperature below 800oC, mixed phases of spinel and μ-cordierite phase after calcination at 800oC and 900oC, and mixed phases of spinel, μ- cordierite and α-cordierite phases after calcination at above 900oC. The BET specific surface areas of the calcined powders varied from 3 to 107 m2/g, depending on calcination temperature. The highest specific surface area of 107 m2/g was found in the powders calcined at 800oC. The average particle sizes evaluated by BET were less than 60 nm, depending on calcination temperature. The powders calcined at 800oC and 1000oC were uniaxially pressed and pressureless-sintered in air at 1250-1350oC for 2h. Densities of the sintered samples evaluated by Archimedes’s method were 87- 91 % of theoretical value. The crystal structure of all the sintered samples, determined by XRD, was mainly α-cordierite, having a small amount of spinel as second phase.
42
Saveliev, Dmitri E., Darkhan K. Makatov, Ildar R. Rakhimov, Ruslan A. Gataullin, and Vladimir V. Shilovskikh. "Silicates from Lherzolites in the South-Eastern Part of the Kempirsay Massif as the Source for Giant Chromitite Deposits (the Southern Urals, Kazakhstan)." Minerals 12, no. 8 (August 22, 2022): 1061. http://dx.doi.org/10.3390/min12081061.
Анотація:
We provide results of a comprehensive mineralogical and microstructural study of relict lherzolites of the main ore field and fresh rocks from a deep structural borehole drilled in the south-eastern part of the Kempirsay massif. Olivine and orthopyroxene from lherzolites contain numerous pieces of evidence of material redistribution at different scales caused mainly by solid-state processes, such as plastic flow of mantle, syntectonic recrystallization, and annealing. The results of deformation-induced processes at the submicron scale are recorded by optical and electronic microscopy. In olivine, the plastic deformation caused segregation of impurities at structural defects. As a result, abundant tiny rods of newly formed Cr-spinels occurred inside its grains. Moreover, in enstatite, deformation caused partial or complete chemical decomposition with exsolution of diopside, pargasite and spinel lamellae up to the formation of a “fibrous” structure. In other cases, it provided partial or complete recrystallization to form new phases of enstatite-2, forsterite, diopside, pargasite, and spinel. Petrographic observations are validated by geochemical data, i.e., regularly decreasing concentrations of minor elements in neoblasts compared to large grains (porphyroclasts). Further redistribution of spinel grains with the formation of chromitite bodies is witnessed by their permanent association with the most mobile phase of the upper mantle, i.e., olivine, which is the only mineral that remains stable under the intense plastic flow. An increased concentration of Cr-spinel grains during formation of massive chromitites could appear under conditions close to pressure sintering, as evidenced by stressed textures of ores and an increased grain size compared to disseminated chromitites. The formation of unique chromitite deposits is associated with integration of numerous disparate podiform bodies into “ore bunches” due to the tectonic impact in the shear-compression regime. This was most likely associated with transition of the rifting (spreading) regime to that of the upper mantle of the fore-arc basin.
43
Konopka, Katarzyna. "Shape, Size and Distribution of Metal Particles Embedded in a Ceramic Matrix." Solid State Phenomena 231 (June 2015): 57–63. http://dx.doi.org/10.4028/www.scientific.net/ssp.231.57.
Анотація:
The presented paper is a review of own work done on two systems of composites, Al2O3‑Ni and Al2O3-Fe. The previous own results of research into shape, size and distribution of the metal particles and spinel phase embedded in a ceramic matrix are referred to and new ones are presented. Metal particles as well as spinel can be distributed uniformly in a ceramic matrix or can form graded structures. Most often there are agglomerates of metal or spinel particles rather than separated particles embedded in ceramic grains. In composites the growing spinel forms a thick oval layer around a metal particle, however, separate spinel areas embedded in a ceramic matrix are noticed, too. Also, the characteristic “doughnut” shape of spinel is found. Since the metal and spinel phase influence the mechanical properties, the required properties of ceramic-metal composites can be tailored by changing the size, shape and distribution of the phases.
44
Berand, N., H. Haeuseler, and K. J. Range. "Hochdruckreaktionen quaternärer Chalkogenide mit Schichtstruktur / High-Pressure Reactions of Quaternary Layered Chalcogenides." Zeitschrift für Naturforschung B 51, no. 6 (June 1, 1996): 785–89. http://dx.doi.org/10.1515/znb-1996-0605.
Анотація:
Abstract The layered chalcogenides CoGa1.7Ti0.3S4, CoGa1.7V0.3, CoGa1.6Cr0.4S4, CoGaInS4, MnGa1.5Cr0.5S4, MnGa1.4Sc0.6S4, MnGa0.8In1.2S4, MnIn2S1.6Se2.4 and CdIn2S2.1 Se1.9 have been investigated under high-pressure - high-temperature conditions (p ≤ 60 kbar, T ≤ 1600°C). MnIn2S1.6Se2.4 and CdIn2S2.1,S1.9 show a phase transition to spinel-type compounds (a = 11.022(2) and a = 11.059(1) Å, respectively). MnGa0.8In1.2S4 forms a high-pressure polymorph with an olivine-type structure (a = 12. 856(3), b = 7.500(3), c = 6.128(2)Å. All other compounds decompose under the conditions applied. The results of a Rietveld structure refinement for the two high-pressure spinels are presented
45
Pradhan, Swapan Kumar, Sumanta Sain, and Hema Dutta. "Microstructure Characterization of Nanocrystalline Magnesium Ferrite Annealed at Elevated Temperatures by Rietveld Method." ISRN Ceramics 2011 (December 14, 2011): 1–8. http://dx.doi.org/10.5402/2011/194575.
Анотація:
Nanocrystalline magnesium ferrite is synthesized at room temperature by high energy ball milling the MgO and α-Fe2O3 (1 : 1 mol fraction) powders. The Rietveld structure and microstructure refinements of X-ray powder diffraction data of 9 h milled sample reveal the presence of mixed and nearly inverse spinel nanocrystalline Mg-ferrite phases. Postannealing of nanocrystalline powder within 873–1473 K reveals continuous change in cation distribution among the tetrahedral and octahedral sites of mixed spinel lattice leading to nearly inverse spinel structure with increasing temperature. Mixed spinel structure finally transformed into inverse spinel structure after 1 h of annealing at 1073 K. The ferrite phase becomes completely stoichiometric by solid-state diffusion of unreacted (∼0.3 mol fraction) α-Fe2O3 into spinel lattice after 1 h of annealing at 1273 K. Interestingly, particle sizes of ferrite phases do not increase considerably up to 1073 K and increase suddenly after transformation of mixed spinel into nearly inverse spinel structure.
46
Cheng, Jin Shu, Jing Wang, Li Ying Tang, and Zhen Lu Deng. "Crystallization Kinetics of MgO–Al2O3–SiO2 Transparent Glass–Ceramics." Key Engineering Materials 509 (April 2012): 230–34. http://dx.doi.org/10.4028/www.scientific.net/kem.509.230.
Анотація:
The non-isothermal crystallization kinetics of the MgO–Al2O3–SiO2 (MAS) glasses were analyzed with the Kissinger equation and the Augis-Bennett equation by differential scanning calorimeter (DSC) and X-ray diffraction (XRD). The results showed that two crystal phases of spinel (MgAl2O4) and SiO2 were generated sequentially in the heat treatment process. When the spinel was the only crystal phase, the MAS glass-ceramic was transparent. For glass A (containing one type alkali metal Na2O), the corresponding activation energy was Ep1(A)=325.27kJ/mol, Ep2(A)=364.99kJ/mol; for glass B (containing Na2O and K2O) , the activation energy is Ep1(B)=233.79kJ/mol, Ep2(B)=273.85kJ /mol. The average crystallization index for spinel crystal phase was nA1=1.99, nB1=2.58, By adding K+, which suggested that the spinel crystal phase precipitation have the trend to change from two-dimensional pattern to bulk crystallization.
47
Lodha, Rahul, Carmen Oprea, Tom Troczynski, and George Oprea. "Sintering Studies on Magnesia-Rich Chromium-Free Spinel-Bonded Basic Refractories." Advances in Science and Technology 70 (October 2010): 108–13. http://dx.doi.org/10.4028/www.scientific.net/ast.70.108.
Анотація:
Basic bricks with Cr2O3 from chrome ore, as the spinel forming oxide, are used in the non-ferrous industry because of their corrosion resistance against fayalite-type slags, rich in FeO. Our objective in this study was to replace Cr3+ with Me4+ ions, which along with Fe3+ could maintain the spinel formation capability with MgO and perform similarly against fayalite slags in non-ferrous furnaces. Our preliminary research studies showed that Cr-free spinels in the MgO-Al2O3-FeOx-Me4+O2 systems could perform against fayalite slags similar to the complex (Mg2+, Fe2+)O·(Cr3+, Fe3+, Al3+)2O3 spinel, the main corrosion resistant component in the magnesia-chrome bricks. The incorporation of iron oxide in the MgO-Al2O3-Me4+O2 systems would contribute to reactive sintering and also in decreasing the solubility of both the ferrous and ferric ions present in the fayalite slag. Phase analysis on stoichiometric mixes showed that the use of tetravalent cation oxides like tin dioxide (SnO2) and titanium dioxide (TiO2) can induce high solubility of spinel in magnesia. In order to maintain charge balance, two trivalent cations were replaced by a tetravalent and a bivalent cation causing the additional bivalent cation to occupy the octahedral position thereby creating an inversion in position of the bivalent ions similar to the behaviour exhibited by Fe3+ occupying tetrahedral site in complex spinel phase of magnesia-chrome ceramics. Most of the magnesia-chrome refractories have ~60 wt. % MgO and hence our experimental mixes contained that amount and called “magnesia-rich” compositions, to be distinguished from the stoichiometric MgAl2O4 spinel. Our findings showed that the incorporation of nano TiO2 powders reduces the temperature of spinel formation as the diffusion path is shortened and thus activates both synthesis and sintering. Compositions containing 60 wt. % magnesia with alumina, nano TiO2 and Fe2O3 fired below 1500°C for 3 hours resulted in complete spinel formation and open porosity less than 5%.
48
Wu, E., S. J. Campbell, W. A. Kaczmarek, M. Hofmann, and S. J. Kennedy. "Nanostructured (Co x Fe1– x )3–y O4 spinel – mechanochemical synthesis." International Journal of Materials Research 94, no. 10 (October 1, 2003): 1127–33. http://dx.doi.org/10.1515/ijmr-2003-0204.
Анотація:
Abstract The effects of wet-milling mixtures of α-Fe2O3 and cobalt hydroxide Co(OH)2 over a range of Co/Fe ratios for 215 h have been investigated by neutron diffraction and Mössbauer spectroscopy. The starting materials were mixed according to the stoichiometric formula (Co x Fe1 –x )3O4 for values of x = 0.037, 0.071, 0.133, 0.234 and 0.380 (i. e., from ≈ Co0.1Fe2.9O4 to the cobalt spinel CoFe2O4). These studies reveal the formation of a nanostructured, mixed Co–Fe spinel phase with non-stoichiometric composition (Co x Fe1– x )3 –y O4; the defect spinels have refined values x c = 0.04, 0.08 and 0.14 for the mixtures with the lowest Co content (x = 0.037, 0.071 and 0.133) and defect concentrations in the range y ≈ 0.1 –0.2. Both the spinel phase and un-reacted α-Fe2O3 are found to occur in the neutron diffraction patterns and Mössbauer spectra for the high Co content mixtures x = 0.234 and x = 0.380. Rietveld refinements of the neutron data indicate that the Co atoms predominantly occupy the octahedral B sites with vacancies also found to be located on the octahedral B sites. Analyses of the Mössbauer spectra of the milled samples confirm the existence of vacancy defects in the B sites and reveal that the vacancies cause similar effects to those of the Co ions, leading to a higher average charge state per iron atom.
49
Bereczki, Laura, Vladimir M. Petruševski, Fernanda Paiva Franguelli, Kende Attila Béres, Attila Farkas, Berta Barta Holló, Zsuzsanna Czégény, Imre Miklós Szilágyi, and László Kótai. "[Hexaamminecobalt(III)] Dichloride Permanganate—Structural Features and Heat-Induced Transformations into (CoII,MnII)(CoIII,MnIII)2O4 Spinels." Inorganics 10, no. 12 (December 9, 2022): 252. http://dx.doi.org/10.3390/inorganics10120252.
Анотація:
We synthesized and characterized (IR, Raman, UV, SXRD) hexaamminecobalt(III) dichloride permanganate, [Co(NH3)6]Cl2(MnO4) (compound 1) as the precursor of Co–Mn–spinel composites with atomic ratios of Co:Mn = 1:1 and 1:3. The 3D−hydrogen bond network includes N–HO–Mn and N–HCl interactions responsible for solid-phase redox reactions between the permanganate anions and ammonia ligands. The temperature-limited thermal decomposition of compound 1 under the temperature of boiling toluene (110 ∘C) resulted in the formation of (NH4)4Co2Mn6O12. which contains a todorokite-like manganese oxide network (MnII4MnIII2O1210−). The heat treatment products of compounds 1 and [Co(NH3)5Cl](MnO4)2 (2) synthesized previously at 500 ∘C were a cubic and a tetragonal spinel with Co1.5Mn1.5O4 and CoMn2O4 composition, respectively. The heating of the decomposition product of compounds 1 and 2 that formed under refluxing toluene (a mixture with an atomic ratio of Co:Mn = 1:1 and 1:2) and after aqueous leaching ((NH4)4Co2Mn6O12, 1:3 Co:Mn atomic ratio in both cases) at 500 ∘C resulted in tetragonal Co0.75Mn2.25O4 spinels. The Co1.5Mn1.5O4 prepared from compound 1 at 500 ∘C during the solid-phase decomposition catalyzes the degradation of Congo red with UV light. The decomposition rate of the dye was found to be nine times faster than in the presence of the tetragonal CoMn2O4 spinel prepared in the solid-phase decomposition of compound 2. The todorokite-like intermediate prepared from compound 1 under N2 at 115 ∘C resulted in a 54 times faster degradation of Congo red, which is a great deal faster than the same todorokite-like phase that formed from compound 2 under N2.
50
Azzoni, C. B., M. C. Mozzati, A. Paleari, V. Massarotti, M. Bini, and D. Capsoni. "Evidence of a Cationic Substitution Domain in Lithium-Manganese Spinels." Zeitschrift für Naturforschung A 53, no. 9 (September 1, 1998): 771–78. http://dx.doi.org/10.1515/zna-1998-0907.
Анотація:
Abstract Magnetic susceptibility measurements and electron paramagnetic resonance spectra of samples prepared from the reactive system MnO/Li2CO3 with different starting Li cationic fraction x are analyzed, taking into account the structural and compositional information provided by x-ray diffraction. Parent phases, as Mn2O3 , Mn3O4 and Li2 MnO3 , arise together with the lithium-manganese spinel as a result of Li-deficiency or Li-excess with respect to the x = 0.33 composition pertinent to the stoichiometric LiMn2O4 spinel. The data show that the spinel phase can sustain a partial Li-Mn substitution in the cation sites, according to compositional models described, for x > 0.33, by Li1+y Mn3+1-3y Mn4+1+2y O4 (Li-rich spinel) and, for x< 0.33, by Li1-|y| Mn2+|y| Mn3+1+|y| Mn4+1-|y| O4 (Li-poor spinel). Paramagnetic resonance data of the Li-poor spinel phase are analyzed to discuss the possible oxidation state of Mn in the tetrahedral site.