Formation Of Fayalite Research Articles

Fayalite from Fe-rich paralavas of ancient coal fires in the Kuzbass, Russia

Fayalite is a common mineral of Fe-rich paralavas related to spontaneous combustion of coal seams. Fayalite has also been found in parabasalts from burned coal waste piles of the Chelyabinsk coal basin. Among paralavas from different combustion metamorphic (CM) complexes of the world, fayalite is the most widespread in the fused rocks of the Kuznetsk coal basin (Kuzbass) and the Ravat area in Tajikistan. The optimal conditions for fayalite formation as products of coal fires in the Kuzbass and Ravat resulted from a favorable combination of the composition of fused protolith (parental rocks) composed of pelitic and Fe-rich sediments and the redox conditions of the deep subsurface (\( f_{O_2 } \) is lower than the QFM buffer). In the Kuzbass, fayalite is commonly hosted in high-silica aluminous Fe-rich paralavas composed of Fe-cordierite (sekaninaite), tridymite, hercynite-magnetite, cristobalite, aluminous clinoferrosilite, and Al-K silicic glass. The composition of all Kuzbass fayalites is close to the Fe2SiO4 end member. Kuzbass fayalites are characterized by a negligibly low CaO content and higher MnO and P2O5 contents like fayalites from burned rocks of other CM complexes. In Kuzbass paralavas, Fe-olivine is the late phase that crystallized after sekaninaite and tridymite, immediately before melt quenching.

Specific features of the formation of fayalite in reduced systems

Specific features of the formation of fayalite in reduced systems

Influence of TiO2 and Cr2O3 on crystallinity and properties of Ca, Li aluminosilicate glass

The influence of TiO2 and Cr2O3 on the crystallisation behaviour of a glass system based on CaO–Li2O–Al2O3–SiO2 has been studied. Local limestone and clays were used as raw materials in the batch composition. Various thermal, microscopic and diffractometric techniques were used to investigate the amorphous and crystalline phases present. Heat treatment led to the formation of β-eucryptite, wollastonite, anorthite and fayalite. Both parent and Cr2O3 containing glasses showed enhanced crystallisation of β-eucryptite and wollastonite, whereas anorthite formation was catalysed in TiO2 containing glasses, in addition to the latter phases mentioned. Crystallisation of all glasses at 1100°C reduced wollastonite formation to trace levels; however, fayalite appeared in Cr2O3 containing samples. Glass–ceramics with a homogeneous bulk microstructure were developed, mainly characterised by accumulated fine rounded to subrounded crystals of 2·5–10 μm diameter of β-eucryptite phase. Intergranular rhombic-like and fibrous crystals were also developedand may be wollastonite and anorthite respectively, in TiO2 containing samples. Depending on the content of β-eucryptite and other phases in the glass–ceramic samples, the coefficient of thermal expansion ranged from −8·75 × 10−7°C−1 (25–300°C) to 54·16 × 10−7°C−1 (25–680°C). The Vickers microhardness of glass–ceramic samples ranged between 676 and 593 kg mm−2 and was high for anorthite containing samples.

Insertion of iron oxide in calciumsilicate gel-derived materials

Samples of the composition of 10Fe2O3·10CaO·80SiO2 were prepared by the sol-gel method and heat-treated in different atmospheres. They were investigated by X-ray diffraction, scanning electron microscopy and Mossbauer spectroscopy. In the heat-treated samples in air iron is present up to 1000 °C in form of hematite and as Fe3+ in the tetrahedral sites. A wide range of hematite particle sizes was observed, the average size increased with heating temperature. At 1000 °C wollastonite was observed, at 1200 °C tridymite was formed and all the iron was incorporated in hematite. A heat-treatment at 500 °C under reducing conditions led to poorly crystallized maghemite and at 700 °C to metallic iron and fayalite formation.

Silicon as an alloying element in ferrite stainless steels containing 8–13% Cr

A jumpwise improving of the passivation ability and pitting-resistance of the Fe-(8–13)% Cr-(0.32–2.7)% Si alloys upon surpassing the limit of ∼14–15 at % by the chromium and silicon summary concentration is found. It is suggested that the nature of the critical summary concentration CCr + CSi is identical to that in Fe-Cr binary alloys; it is caused by the silicon building-in to the alloy’s crystal lattice and its substitution for chromium in the statistical proportion to its atomic part in alloys. When the summary concentration CCr + CSi approaches ∼14–15 at %, each elementary cell in the Fe bcc lattice must necessarily contain either a Cr atom or the proportional number of Si atoms. The improved passivation ability and pitting-resistance of the Fe-Cr-Si alloy, compared with the Fe-Cr alloys, is explained by the fayalite formation at the alloy surface.

Thermodynamic constraints on fayalite formation on parent bodies of chondrites

Abstract— Thermochemical equilibria are calculated in the multicomponent gas‐solution‐rock system in order to evaluate the formation conditions of fayalite, (Fe0.88–1.0Mg0.12–0)2SiO4, Fa88–100, in unequilibrated chondrites. Effects of temperature, pressure, water/rock ratio, rock composition, and progress of alteration are evaluated. The modeling shows that fayalite can form as a minor secondary and transient phase with and without aqueous solution. Fayalite can form at temperatures below ˜350 °C, but only in a narrow range of water/rock ratios that designates a transition between aqueous and metamorphic conditions. Pure fayalite forms at lower temperatures, higher water/rock ratios, and elevated pressures that correspond to higher H2/H2O ratios. Lower pressure and water/rock ratios and higher temperatures favor higher Mg content in olivine. In equilibrium assemblages, fayalite usually coexists with troilite, kamacite, magnetite, chromite, Ca‐Fe pyroxene, and phyllosilicates. Formation of fayalite can be driven by changes in temperature, pressure, H2/H2O, and water/rock ratios. However, in fayalite‐bearing ordinary and CV3 carbonaceous chondrites, the mineral could have formed during the aqueous‐to‐metamorphic transition. Dissolution of amorphous silicates in matrices and/or silica grains, as well as low activities of Mg solutes, favored aqueous precipitation of fayalite. During subsequent metamorphism, fayalite could have formed through the reduction of magnetite and/or dehydration of ferrous serpentine. Further metamorphism should have caused reductive transformation of fayalite to Ca‐Fe pyroxene and secondary metal, which is consistent with observations in metamorphosed chondrites. Although bulk compositions of matrices/chondrites have only a minor effect on fayalite stability, specific alteration paths led to different occurrences, quantities, and compositions of fayalite in chondrites.

Influence of plasma on formation of crystalline Fe 2SiO 4 grains

The production of Fe 2SiO 4 (fayalite) crystalline grains was performed by two processes, namely, grain formation in a plasma field by evaporating a mixture powder of Fe and SiO and heat treatment of the product collected on the radio-frequency (RF) electrode side. Fe grains <20 nm in size covered with an amorphous SiO layer selectively formed Fe 2SiO 4 grains by heating at 800 °C. By heating at 600 °C, in addition to the formation of Fe 2SiO 4 crystal grains, the FeO phase appeared. The doping effect of excited oxygen in a plasma field into the Fe small grains may be the trigger on the formation of fayalite through the FeO phase formation. The present experimental result suggests that the probability of Fe 2SiO 4 grain formation in space is low.

Geology and SHRIMP U-Pb Geochronology of the Igarape Bahia Deposit, Carajas Copper-Gold Belt, Brazil: An Archean (2.57 Ga) Example of Iron-Oxide Cu-Au-(U-REE) Mineralization

A striking feature of the Carajas region, Brazil, is the clustering of a variety of different types of Cu-Au deposits. The most abundant in the belt are the >200 million metric tons (Mt) of Fe oxide Cu-Au-(U-REE) deposits, which, despite the variety of host rocks and different orebody morphologies, share a number of diagnostic features, including (1) intense Fe metasomatism leading to the formation of grunerite, fayalite, and/or Fe oxides (magnetite and/or hematite); (2) intense carbonate alteration (mainly siderite); (3) sulfur-poor ore mineralogy (chalcopyrite and bornite); (4) quartz-deficient gangue; (5) extreme low REE enrichment, and (6) enrichment in U and Co. The Igarape Bahia deposit is perhaps the best documented Fe oxide Cu-Au-(U-REE) deposit of the belt, containing about 219 Mt at 1.4 percent Cu and 0.86 g/t Au. The Cu-Au ore consists of steeply dipping breccia bodies that are hosted by hydrothermally altered metavolcano-sedimentary rocks. SHRIMP II zircon dating of the host metavolcanic rocks gives a 207Pb/206Pb age of 2748 ± 34 Ma. This suggests a correlation between the Igarape Bahia volcano-sedimentary sequence and the Grao Para volcanic rocks, which have published ages of ca. 2.75 Ga. SHRIMP dating of monazite from the matrix of ore-bearing magnetite breccias gives a 207Pb/206Pb age of 2575 ± 12 Ma, confirming the epigenetic nature of the mineralization and placing it ~175 m.y. after accumulation of the host volcano-sedimentary sequence. The 2575 ± 12 Ma SHRIMP age of hydrothermal monazite from the Igarape Bahia mineralization is indistinguishable from published conventional 207Pb/206Pb ages for zircons from the Archean A-type granites of the Carajas belt, indicating that mineralization processes at Igarape Bahia were temporally related to these A-type Archean granites. The wide range of highly radiogenic 87Sr/86Sr ratios (0.714–0.755) of carbonates from the Igarape Bahia deposit suggests multiple crustal sources, consistent with a magmatic-hydrothermal origin. SHRIMP dating of zircon xenocrysts recovered from crosscutting diabase dikes indicates a maximum 207Pb/206Pb age of ~2670 Ma, consistent with field evidence and the age of host rocks, but does not unequivocably constrain the age of the ores. The styles of hydrothermal alteration, mineralogy, and geochemistry of the Igarape Bahia ore, as well as published fluid inclusion and stable isotope data, support its classification as a member of the world-class Olympic Dam-type Fe oxide Cu-Au-(U-REE) group of deposits, as previously argued by several authors. The SHRIMP age of 2575 ± 12 Ma for hydrothermal monazite indicates that Igarape Bahia is an Archean example of this deposit group.

Effect of reductive roasting on smelting characteristics of Greek nickel laterites

Research was undertaken to determine the effect of the reductive roasting conditions on the smelting characteristics of nickel laterite ores from three different areas of Greece—Evia, Viotia and Kastoria. The roasting experiments were performed in a rotary kiln at 800°, 860° and 900°C for 10-90 min; the smelting experiments were carried out in an electric-arc furnace that allowed the melting temperature and energy consumption to be monitored. The melting temperature values of the ore and roast samples were also determined with a LECO AF 600 instrument by enploying the Seger cones technique. The Evia samples, in which the SiO2/Fetot ratio was higher than in the ores from Viotia and Kastoria, exhibited the highest melting temperatures. The lowest values were observed for the Kastoria samples owing to the presence of serpentine, which had a positive effect on their fusibility. Reductive roasting of the Evia and Viotia ore samples was beneficial for the subsequent smelting stage, but roasting of the Kastoria samples resulted in an increase in the melting temperature, possibly on account of the production of refractory oxides. Finally, in agreement with the generally accepted view that reductive roasting has a positive effect on the subsequent smelting operation, increases in the temperature and duration of roasting of a composite laterite ore sample resulted in lower energy consumption during the reductive smelting, which was attributed to fayalite formation.

Evidence for low‐temperature growth of fayalite and hedenbergite in MacAlpine Hills 88107, an ungrouped carbonaceous chondrite related to the CM‐CO clan

Abstract— The carbonaceous chondrite MacAlpine Hills (MAC) 88107 has bulk composition and mineralogy that are intermediate between those of CO and CM chondrites. This meteorite experienced minor alteration and a low degree of thermal metamorphism (petrologic type 3.1) and escaped post‐accretional brecciation. The alteration resulted in the formation of fayalite (Fa90–100). Al‐free hedenbergite (∼Fs50Wo50), phyllosilicates (saponite‐serpentine intergrowths), magnetite, and Ni‐bearing sulfides (pyrrhotite and pentlandite). Fayalite and hedenbergite typically occur as veins, which start at the opaque nodules in the chondrule peripheries, crosscut fine‐grained rims and either terminate at the boundaries with the neighboring fine‐grained rims or continue as layers between these rims. These observations suggest that fayalite and hedenbergite crystallized after accretion and compaction of the fine‐grained rims. Fayalite also overgrows isolated forsteritic (Fa1–5) and fayalitic (Fa20–40) olivine grains without any evidence for Fe‐Mg interdiffusion; it also replaces massive magnetite‐sulfide grains. The initial 53Mn/55Mn ratio of (1.58 ± 0.26) × 10−6 in the MAC 88107 fayalite corresponds to an age difference between the formation of fayalite and refractory inclusions in Allende of either ∼9 or 18 Ma, depending upon the value of the solar system initial abundance of 53Mn used in age calculations.Formation of secondary fayalite and hedenbergite requires mobilization and transport of Ca, Si, and Fe either through a high‐temperature gaseous phase (Hua and Buseck, 1995) or low‐temperature aqueous solution (Krot et al., 1998a, b). The high‐temperature nebular model for the origin of fayalite (Hua and Buseck, 1995) fails to explain (a) formation of fayalite‐hedenbergite assemblages after accretion of fine‐grained rims that lack any evidence for high‐temperature processing; (b) extreme fractionation of refractory lithophile elements of similar volatility, Ca and Al, in hedenbergite; and (c) absence of Fe‐Mg interdiffusion along fayalite‐forsterite boundaries. We conclude that fayalite and hedenbergite in MAC 88107 formed during late‐stage, low‐temperature (approximately 150–200 °C) aqueous alteration. The data for MAC 88107 extend the evidence for an early onset of aqueous activity on chondrite parent bodies and reinforce the conclusion that liquid water played an important role in the chemical and mineralogical evolution of the first chondritic planetesimals.

Effects of Cu and Other Tramp Elements on Steel Properties. Influence of Ni Impurity in Steel on the Removability of Primary Scale in Hydraulic Descaling.

Influences of Ni impurity on the removability of primary scale in hydraulic descaling were investigated in 0.02 and 0.1 mass% Si mild steels. And the thickness distribution of residual scale was discussed in relation to the unevenness of the scale/steel interface. The removability of primary scale reduced due to the existence of Ni impurity ranging to 0.05 mass% in each steel. With an increase in Si content up to 0.1 mass%, the removability of Ni added steels showed heating temperature dependence between 1 150 and 1 250°C. The existence of Ni impurity made the scale/steel interface of steel uneven. Estimating the unevenness of the interface by measuring the interface length, it was found that the austenite transgranular unevenness governs the change in the total interface length rather than the oxide invasion into austenite grain boundaries. A reduction of scale removability caused by Ni impurity was explained by the increased interface length. In spite of the large difference in scale removability between 0.02 and 0.1 mass% Si steels containing more than 0.05 mass% Ni, the unevenness of the scale/steel interface was the identical with each other. Therefore, the temperature dependence of the scale removability in Ni added 0.1 mass% Si steel was not explained by this factor. Other mechanisms concerning fayalite formation and its morphology should be taken into account for this behavior.

Fayalite in the Kaba and Mokoia carbonaceous chondrites

The olivines in the Kaba and Mokoia CV3 carbonaceous chondrites range from almost pure forsterite (Fo 99.6) to almost pure fayalite (Fa 99.9)). Individual grains of fayalite of such high purity have not previously been reported from meteorites; they can reach 100 μm in diameter and occur in the matrix, chondrules, forsterite-enstatite aggregates, and rims around Ca, Al-rich inclusions, chondrules, and aggregates. The fayalite is three to nine times richer in Mn than in bulk CI chondrites. Many grains are associated with magnetite, troilite, and pentlandite, an assemblage that suggests relatively oxidizing conditions. We propose that the fayalite formed through reaction of SiO(g), released by decomposition of enstatite, with magnetite and sulfide. The lower thermal limit for fayalite formation is determined by the above reaction, whereas the upper thermal limit is controlled by magnetite stability. Thermodynamic calculations indicate that fayalite coexisting with magnetite and sulfides could have formed in a nebular environment that had a H 2 O H 2 ratio substantially greater than the canonical solar nebula. Coexisting olivines having endmember compositions indicate that they experienced little or no thermal metamorphism.

Fayalite-silica association in unequilibrated ordinary chondrites: Evidence for aqueous alteration on a parent body

We report ten occurrences of high-fayalite (Fa56–99 mol%; four with Fa> 82 mol%) olivine in association with silica in type-3 ordinary chondrites. Pyroxene with high Fs contents is much less common; Fs contents do not exceed 66 mol%, and most maxima are < 50 mol%. In those cases where the amount of fayalite is minor relative to that of silica, the fayalite forms a layer on the silica, and shows textural evidence of formation by reaction of silica with oxidized Fe; the latter seems to have resulted from reaction of metallic Fe—Ni with an oxidant, most likely H 2O vapor. The fayalite is generally in contact with pyroxene (and, in one case, olivine) having much lower Fe/(Fe + Mg) ratios, indicating that lattice diffusion has been minimal. Formation of fayalite from SiO 2 explains the low Mg content of this olivine; the Mg was sequestered inside the lattices of mafic minerals and was thus inaccessible. In contrast, the moderately high Mn contents of the fayalite indicate that an appreciable fraction of the Mn in the precursor assemblage was accessible; it was probably sited in the matrix in the form of tiny, poorly crystallized oxide grains produced by nebular condensation at temperatures too low to permit diffusion into forsterite or enstatite. The reaction of SiO 2 with FeO produced by oxidation (during metamorphism) of Fe—Ni can also account for fayalitic olivine associated with SiO 2 microspherules in the fine-grained matrices of type-3 ordinary chondrites and, because matrix is SiO 2 normative, for other occurrences of fayalite in matrix. The presence of Mn in the fayalitic rims on the olivine of carbonaceous chondrites does not require a nebular origin.

銅スラグの結晶化と金属元素の溶出性

Non-ferrous slags are becoming widely used in these days, the usage is however far from satisfactory level. In order to resolve the problem, it is important to develop new processes or to produce new materials which have higher values added from the slags.In the present study, the effect of the cooling condition of copper slag melts on retained glass and crystalline phases was investigated. Simultaneously, the dissolution test decided by the Ministry of Environment was carried out for the samples.The critical cooling rate for glass forming determined from the CCT diagram was 100°C/sec. The crystalline phase detected by X-ray diffraction was only fayalite as far as heat treatment was conducted in the H2: CO2 1: 1 atmosphere in which wustite was stable. Magnesia formed the solid solution with fayalite, and lime and alumina were rich in glassy matrix which was consisted with low iron and high silica.Dissolved concentrations of all metallic components from the water-granulated slags were under the standard of drinking water, and these from heat-treated slags were same except for iron. Iron dissolution from slags increased with decreasing cooling rate, and it may be attributed to the fayalite formation. Dissolved concentration of iron from furnace-cooled slag, however, was under the standard of waste water. After all, the dissolution of metallic components from copper slags was less than the regulation level, so the slags would not contaminate the environment.

AES and CEMS analysis of the formation of layers on Si steel under thermal treatment in a flux of H2/water vapour

The near surface diffusion and reaction processes in iron-silicon steel (3.1 wt.%Si) during 10 min decarburization in water vapour/hydrogen have been studied. The decarburization temperature has been varied between 506 and 714°C for the fixed partial pressure ratio pH2O/pH2=0.017. An outer layer of SiO2 forms on the surface with its thickness increasing with temperature. From 600°C upwards, the decarburization process is hindered and a cementite layer is formed below the SiO2 layer. The formation of fayalite at the surface has been studied at a fixed decarburization temperature with pH2O/pH2 ranging from 0.017 to 0.49. The scale thickness reduces abruptly just before the ratio pH2O/pH2 necessary for the wustite formation is reached. Obviously, a new layer is formed which reduces the oxygen diffusion that much that a transition from internal to external oxidation occurs.

Effect of light ash of solid fuels on zirconia refractories

The action of the melts of the light ash of the Kuznetsk and the Berezovsk coals containing potash additive on zirconia refractories leads to their destruction due to destabilization of the cubic solid solution of CaO in ZrO2 accompanied by the formation of α-ZrO2, melilites, and a glass phase and the formation of spinellids, pyroxenes, and fayalite if iron-bearing compounds are present in the ash. Intensive destruction of the CaO-stabilized zirconia refractory under the action of a mixture of the Berezovsk ash and potash is due to its low melting point and the high degree of saturation of the refractory with the melt additionally containing iron compounds. The service life of the zirconia refractories subjected to the action of a mixture of the ash of the Kuznetsk coal and potash is longer owing to the smaller degree of melt penetration at a temperature up to 1580°C.

Oxidation Inhibition Mechanism and Performance of a New Protective Coating for Slab Reheating

The properties of a newly developed oxidation inhibitor composed of refractory powder, SiO2, aluminum, synthetic mica, colloidal silica and coking bond were clarified and the oxidation inhibition mechanism of this inhibitor was examined. This inhibitor is applicable to all steel grades and significantly improves their yields. At the same time, it completely eliminates surface defects due to scale by suppressing the intergranular oxidation and selective oxidation of alloying elements. During reheating, the metallic silicon in the film of the inhibitor decomposes mullite (3Al2O3• 2SiO2) and SiO2 to form metallic silicon. This metallic silicon is oxidized with a gradual formation of protective amorphous SiO2, which then prevents the diffusion of O2. After the decomposition of mullite and SiO2, aluminum is oxidized and forms an α-Al2O3 film and an FeO•Al2O3 film, which are also highly protective. Furthermore, the formation of fayalite (2FeO•SiO2) is suppressed in this inhibitor due to the formation of FeO•Al2O3. Therefore, the protective films exist stably even if steels are reheated at high temperatures for a long time. In addition, many pores are formed due to a decrease in volume resulting from the chemical changes of Al→Al2O3 and SiO2→Si. These pores constitute barriers to the diffusion of Fe++ and O--. The excellent oxidation-preventive capacity of this inhibitor is due to the combined actions mentioned above.

Mechanism of growth of metallic phase in direct reduction of iron bearing oolites

The direct reduction of oolites involves progressive growth of the metallic phase with temperature. Two orders of magnitude increase in particle size are observed at 1100 °C followed by the formation of a continuous metallic phase at 1250 °C. Two growth mechanisms were identified: below 1050 °C particle coarsening, and above 1050 °C the formation of phosphorus rich iron melt. It is shown that particle coarsening can be related to the formation of fayalite and hercynite bridges between particles of different sizes. Finally, the direct reduction and growth mechanisms were correlated to the oolite internal shell structure, spacing of goethite particles, and pore content and size distribution, using electron microscopy, mercury porosimetry, and image analysis.

ファイヤライト (Fe&lt;SUB&gt;2&lt;/SUB&gt;SiO&lt;SUB&gt;4&lt;/SUB&gt;) の生成と還元反応について

ファイヤライト (Fe&lt;SUB&gt;2&lt;/SUB&gt;SiO&lt;SUB&gt;4&lt;/SUB&gt;) の生成と還元反応について

ファヤライトの生成機構に関する研究

Two sets of experimental work were carried out to study the mechanism of fayalite formation.(1) A fayalite pellet was sandwiched between a wustite and a vitreous silica rod. And a platinum wire as a marker was placed at the interface of wustite and fayalite. Thus arranged specimen was heated at 1150°C for 24 hrs in an argon. The marker was moved into the fayalite pellet and sinter pores in the fayalite were also moved to and accumulated at the interface of fayalite and silica. The vitreous silica was crystallized due probably to a mineralizing action of wustite transferred into the silica. According to an electron-probe micro analyis it was considered that the iron in silica was mainly located in the boundary of the silica crystals.(2) Wustite powder and silica gel were mixed at the composition of fayalite and heated at 1000°C in vacuum for 10 to 600 min. The amount of fayalite formed and of wustite remained were determined by X-ray powder method. The rates of the formation of fayalite and of the reduction of wustite obeyed completely the parabolic rate low. The actual amount of the fayalite formed, however, was always lesser than that of the value calculated from the amount of wustite remained. This discrepancy seemed to be due to the presence of wustite acting as a mineralizer in silica.The mechanisms of the mineralizing action of wustite and the formation of fayalite were dicussed.