Magnetite Content Research Articles

Controlled Synthesis of Magnetic Iron Oxide Nanoparticles: Magnetite or Maghemite?

Today, magnetic nanoparticles are present in multiple medical and industrial applications. We take a closer look at the synthesis of magnetic iron oxide nanoparticles through the co-precipitation of iron salts in an alkaline environment. The variation of the synthesis parameters (ion concentration, temperature, stirring rate, reaction time and dosing rate) change the structure and diameter of the nanoparticles. Magnetic iron oxide nanoparticles are characterized by X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM). Magnetic nanoparticles ranging from 5 to 16 nm in diameter were synthesized and their chemical structure was identified. Due to the evaluation of Raman spectra, TEM and XRD, the magnetite and maghemite nanoparticles can be observed and the proportion of phases and the particle size can be related to the synthesis conditions. We want to highlight the use of Raman active modes A1g of spinel structured iron oxides to determine the content of magnetite and maghemite in our samples. Magnetite nanoparticles can be derived from highly alkaline conditions even without establishing an inert atmosphere during the synthesis. The correlation between the particle properties and the various parameters of the synthesis was modelled with linear mixture models. The two models can predict the particle size and the oxidation state of the synthesized nanoparticles, respectively. The modeling of synthesis parameters not only helps to improve synthesis conditions for iron oxide nanoparticles but to understand crystallization of nanomaterials.

A rock magnetic perspective of gas hydrate occurrences in a high-energy depositional system in the Krishna-Godavari basin, Bay of Bengal

We conducted a detailed rock magnetic study complemented by sedimentological and mineralogical methods on a 177.2-m-long sediment core of Hole NGHP-01-14A to constrain the influence of high-energy depositional environment on the magnetic mineral diagenesis and formation of gas hydrates in the Krishna-Godavari (K-G) basin, Bay of Bengal. Five sediment magnetic zones were identified based on the downcore variation in rock magnetic parameters. The magnetic mineralogies comprised of detrital titanomagnetite, diagenetically formed magnetic iron sulfides and their mixture. A distinct magnetically enhanced zone (Z-3) close to a bottom simulating reflector (BSR) is dominated by higher magnetite content, sediment bulk density, and grain size and probably represents several sand-rich sediment layers formed as a result of short-duration intense sedimentation events and got rapidly buried and provided conducive environment for the formation of gas hydrate deposits at the studied site. The concurrence of gas hydrates and high gas saturations within the sand-rich layers (Z-3) suggests that the high-energy depositional environment had a larger control over hydrate formation at Hole NGHP-01-14A. Two magnetic iron sulfide bearing sediment intervals in Z-1b and Z-1c below sulfate-methane transition zone (SMTZ) suggest that their formation is controlled by microbially mediated diagenetic reactions fuelled by presence of gas hydrates and probably represents the fossil gas hydrate zones. We propose that the rock magnetic variations in the studied sediment core at Hole NGHP-01-14A is controlled by both differential loading of detrital magnetic minerals as well as hydrate-induced late diagenetic magnetic iron sulfide formation.

Synthesis, Characterization and Application of Chitosan Coated Magnetite Nanoparticles in Drug Delivery

Magnetite nanoparticles were used extensively for various applications. In the present study, magnetite nanoparticles were synthesized and characterized by atomic force microscopy (AFM). AFM images showed that the obtained particles were perfectly spherical. Functionality is afforded to these magnetite nanoparticles by adding biocompatible polymer chitosan during the synthesis. AFM phase image clearly showed that the magnetite core is encapsulated with the polymeric shell. Fourier-transform infrared spectroscopy (FTIR) study showed the chitosan absorption on Fe2O3 nanoparticle surface. The drug sulphamethoxazole was loaded over magnetite nanoparticles and the encapsulation efficiency of drug was calculated at different concentrations of magnetite. The encapsulation efficiency increases with increase in the concentration of magnetite. Thus, an attempt was made in synthesizing drug loaded biopolymer magnetite nanoparticles suitable for targeted drug delivery.

The thermal maturity of sedimentary basins as revealed by magnetic mineralogy

AbstractThe thermal evolution of sedimentary basins is usually constrained by maturity data, which is interpreted from Rock‐Eval pyrolysis and vitrinite reflectance analytical results on field or boreholes samples. However, some thermal evolution models may be inaccurate due to the use of elevated maturities measured in samples collected within an undetected metamorphic contact aureole surrounding a magmatic intrusion. In this context, we investigate the maturity and magnetic mineralogy of 16 claystone samples from Disko‐Svartenhuk Basin, part of the SE Baffin Bay volcanic margin. Samples were collected within thermal contact metamorphic aureoles near magma intrusions, as well as equivalent reference samples not affected by intrusions. Rock‐Eval pyrolysis (Tmax), and vitrinite reflectance (Ro) analysis were performed to assess the thermal maturity, which lies in the oil window when 435°C ≤ Tmax ≤ 470°C and 0.6%–0.7% ≤ Ro ≤ 1.3%. In addition, we performed low‐ (<300K) and high‐temperature (>300K) investigations of isothermal remanent magnetization to assess the magnetic mineralogy of the selected samples. The maturity results (0.37% ≤ Ro ≤ 2%, 22°C ≤ Tmax ≤ 604°C) show a predominance of immature to early mature Type III organic matter, but do not reliably identify the contact aureole when compared to the reference samples. The magnetic assemblage of the immature samples consists of iron sulphide (greigite), goethite and oxidized or non‐stoichiometric magnetite. The magnetic assemblage of the early mature to mature samples consists of stoichiometric magnetite and fine‐grained pyrrhotite (<1 μm). These results document the disappearance of the iron sulphide (greigite) and increase in content of magnetite during normal burial. On the other hand, magnetite is interpreted to be the dominant magnetic mineral inside the contact aureole surrounding dyke/sill intrusions where palaeotemperatures indicate mature to over‐mature state. Interestingly, the iron sulphide (greigite) is still detected in the contact aureole where palaeotemperatures exceeded 130°C. Therefore, the magnetic mineralogy is a sensitive method that can characterize normal burial history, as well as identify hidden metamorphic contact aureoles where the iron sulphide greigite is present at temperatures beyond its stability field.

Development and analysis of highly workable high‐strength heavyweight concrete using magnetite aggregates

AbstractHeavyweight concrete (HWC) is produced by replacing natural aggregates in a concrete mix design with heavyweight aggregates of a higher specific gravity. HWC is mainly used for the prevention of leakage from radioactive containing structures and is hence primarily used in the medical and nuclear energy industries where this property is of particular benefit and importance. Also, high‐strength concrete (HSC) has been increasingly employed in both civil structures, such as high rise buildings and bridges and defense applications. This study makes attempt to develop and evaluate different concrete mixes, which are considered as high‐strength, heavyweight and highly workable in nature. Such mixes use magnetite as the primary aggregate. The three‐mentioned properties of these concrete types have been thoroughly investigated individually; however, there is a limited numbers of literature on the analysis of mix designs dealing with the three‐mentioned properties simultaneously, in which the water/cement ratio variation, and/or variation of the magnetite content have been assessed. In this study, nine highly workable high‐strength HWC mixes have been developed and fresh and hardened properties are discussed. The overall result indicates that the developed mixes satisfied the required high‐strength, heavyweight and highly workable criteria, as well as, compressive strength would increase by increasing the heavyweight aggregate content.

MAGNETICALLY RECOVERABLE POLYMER CATALYST FOR CELLULOSE HYDROGENOLYSIS

A new type of Ru-containing magnetically recoverable catalyst based on a polymer matrix of hypercrosslinked polystyrene (HPS) for the reaction of the hydrogenolysis of microcrystalline cellulose to ethylene and propylene glycol (EG and PG) is proposed. The catalyst is synthesized sequentially in two stages. At the first stage, by means of thermal decomposition of iron (III) salts in the presence of polyols, magnetite particles (Fe3O4) are formed in the pores of the HPS. At the second stage, Ru-containing nanoparticles of the active phase of the catalyst are synthesized on the surface of Fe3O4/HPS. Samples of the original HPS, Fe3O4/HPS and Ru-Fe3O4/HPS were characterized using various physicochemical methods. In particular, it was shown that the synthesized samples of catalysts have a high specific surface area (450 - 750 m2/g, depending on the magnetite content), retain the micro-mesoporous nature of the original polymer, and have a high saturation magnetization (4.0 ± 0.5 emu /g), which makes them easy to separate from the reaction mass by an external magnetic field. According to the results of transmission electron microscopy (TEM), the average diameter of the nanoparticles of the active phase Ru was 2.0 ± 0.5 nm. The hydrogenolysis of cellulose to glycols was carried out under the following conditions: 255 °C; 60 bar H2; 55 min; 0.3 g of cellulose; 0.07 g of catalyst 3% Ru-Fe3O4/HPS; 30 ml of H2O; 0.07 g of Ca(OH)2. Under these conditions, the selectivities for EG and PG were 22.6 % and 20.0 %, respectively. The degree of cellulose conversion reaches 100 %. The catalyst showed good stability under hydrothermal reaction conditions, is easily separated from the reaction mass by an external magnetic field, and can be used in the processes of cellulose-containing biomass conversion.

Magnetic Composite Submicron Carriers with Structure-Dependent MRI Contrast

Magnetic contrast agents are widely used in magnetic resonance imaging in order to significantly change the signals from the regions of interest in comparison with the surrounding tissue. Despite a high variety of single-mode T1 or T2 contrast agents, there is a need for dual-mode contrast from the one agent. Here, we report on the synthesis of magnetic submicron carriers, containing Fe3O4 nanoparticles in their structure. We show the ability to control magnetic resonance contrast by changing not only the number of magnetite nanoparticles in one carrier or the concentration of magnetite in the suspension but also the structure of the core–shell itself. The obtained data open up the prospects for dual-mode T1/T2 magnetic contrast formation, as well as provides the basis for future investigations in this direction.

Neoformation of magnetite during selective metasomatism controlling large-scale positive magnetic anomalies within the Brunovistulian unit (Bohemian Massif)

An airborne magnetometer survey together with field measurements of magnetic susceptibility have distinguished two main granitic suites within the eastern zone of the Brno batholith (the exposed part of the Brunovistulicum). Highly magnetic biotite-amphibole tonalites, forming widespread positive magnetic anomalies (up to 300 nT), have susceptibility (χ) regularly above 5 × 10−3. Less magnetic biotite granites display lower χ values on the order of 1 × 10−4. The metaluminous tonalites significantly differ in whole-rock chemistry (enriched in FeO, MgO, and depleted in SiO2) and degree of fractionation (decreased Rb/Sr and K/Ba ratios) reflecting the distinct microchemistry of Fe-rich mafic silicates (chamosite ~24 wt% FeO). Conversely, more felsic metaluminous to peraluminous biotite granites exhibiting a higher degree of fractionation characteristically contain mafic silicates depleted in Fe2+ (Mg-clinochlore ~20 wt% FeO). The geochemistry of granitoids and chemical composition of mafic phases suggest that increased contents of pure magnetite (TiO2 <0.15 wt%) along with diamond-shaped titanite originated as a result of the reaction between primary magmatic Fe-Ti oxides, annite and anorthite during late oxidation of granitic rocks. The subsolidus oxidation of granitoid has led to releasing of Fe2+ from mafic silicates representing a substantial source of Fe2+ for the formation of pure magnetite in an evolved and crystallized magmatic system under relatively oxidative conditions. The Curie temperature (585–601 °C) and the Verwey transition (-160 °C) demonstrate the absence of titanomagnetite in both types and the overall magnetic properties of granitoids dominated by pure magnetite slightly affected by oxidation. Nevertheless, the more extensive magnetite hematitization in biotite granites indicates a higher degree of oxidation caused by dissociation of a greater amount of water phase in the post-magmatic stage of evolution of a more fractionated felsic melt. The metasomatic transformation of paramagnetic (Fe-rich biotite and amphibole) to ferromagnetic (pure magnetite) phases, well described on granitoid varieties of the Brno batholith, seems to be responsible for the extraordinarily geomagnetic behavior of the entire eastern part of the Brunovistulicum (Slavkov terrane) mostly covered by Paleozoic sediments.

Iron oxide characteristics of the Chinese loess-red clay sequences and their implications for the evolution of the East Asian summer monsoon since the Late Oligocene

The most significant climatic change in East Asia involved the formation and evolution of the coupled monsoon-arid environmental system during the Cenozoic, which was dynamically linked to global cooling and the growth of the Qinghai-Tibet Plateau. However, our understanding of monsoon evolution since the Late Oligocene remains controversial due to differences in the interpretation of various environmental proxies from loess archives. In this study, the composition and relative abundance of pedogenic iron oxides of two eolian sequences from the Lingtai section and the Zhuanglang drill core were investigated using rock magnetic, optical spectroscopy, and geochemical analyses. The results indicate that while the composition of iron oxides in the Mio-Pliocene red clay and Quaternary loess-paleosol sequences is similar, the concentrations of magnetite, maghemite, hematite and goethite are quite different between loess, paleosol and red clay. The combination of magnetic proxies (magnetic susceptibility, Fed/Fet, and color a* values) reveals that precipitation and temperature played varying roles in driving pedogenesis and chemical weathering since the Late Oligocene. During the Late Oligocene to Early Miocene, the occurrence of relatively strong pedogenesis and chemical weathering was likely the result of high temperatures rather than high precipitation. The East Asian summer monsoon intensified during the Middle Miocene Climate Optimum (16.5–14.5 Ma), in response to global climatic warming; subsequently, during the Middle to Late Miocene, the monsoon intensity gradually weakened due to global cooling. After ~8 Ma, the summer monsoon strengthened substantially and reached a maximum during 4.5–2.6 Ma, possibly as a result of the uplift of the northeastern margin of the Qinghai-Tibetan Plateau during the Late Miocene. The monsoon intensity then commenced a decreasing trend in the Early Pleistocene, but then strengthened again after ~1.0 Ma.

Mineralogy and mineral geochemistry of the Tuwu porphyry Cu deposit, Eastern Tianshan, NW China: implication for the ore-forming condition and Cu mineralization

The Tuwu deposit is one of the largest porphyry copper deposits in Eastern Tianshan, NW China. The widespread hydrothermal alteration is associated with porphyries and their wall-rocks in the porphyry deposit can be divided into potassic, chlorite–sericite, phyllic, and propylitic zones. In this study, we conducted a detailed study on the mineralogy of hydrothermal magnetite, mica, and epidote. Magnetite is closely related to the potassic alteration, and evolves from earlier disseminated magnetite (Mt-I) to the later magnetite–quartz ± biotite ± pyrite ± bornite ± chalcopyrite veins (Mt-II). The significant decrease in the Cr2O3 and V2O3 contents of magnetite from early to late period indicates the gradual increase of oxygen fugacity. The crystallization of magnetite supplies enough reduced sulfur that promotes the sulfide precipitation. The dominance of muscovite (Mc-I) in the early phyllic stage and the increasing of phengite muscovite (Mc-II) in the late phyllic stage suggest the evolution of hydrothermal fluid from a high-temperature and acidic environment to a low-temperature and less acidic environment. This process also results in the decrease of sulfide mineral deposition in the late phyllic stage. Epidote from propylitic zones at Tuwu has similar characteristic with the overprinting epidote in the Yandong porphyry Cu systems. Propylitic Ep-I have higher FeO content than Ep-II. The interaction of Fe-rich propylitic epidote with hydrothermal fluid enhanced both Ca2+ activity and pH value, and favored the precipitation of sulfides (e.g., chalcopyrite). In addition, the Fe-rich and less acidic fluids, which derived from the propylitic zones and flow though the sericitic rocks in the phyllic zones, also promote the deposition of Cu mineralization. Our results, combined with previous research on fluid inclusion, isotopes, and mass transfer, suggest that the changes in temperature, oxygen fugacity, and pH caused by the fluid–rock interaction played a critical role for the Cu mineralization at Tuwu.

МАГНИТНЫЕ ХАРАКТЕРИСТИКИ МЕТАМОРФИЗОВАННЫХ УЛЬТРАБАЗИТОВ ОКЕАНИЧЕСКОЙ ЛИТОСФЕРЫ И ОФИОЛИТОВЫХ КОМПЛЕКСОВ

As part of the study of the nature of magnetic anomalies associated with the deep layers of the oceanic crust, a comparative analysis was made of the petromagnetic characteristics of serpentinized mantle ultrabasic samples taken from oceanographic expeditions of the Institute of Oceanology and the Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences in various morphotectonic regions of the World Ocean. The purpose of the work is to obtain information on the composition, concentration, crystallization temperature and structural features of ferromagnetic minerals, which are formed in different conditions of the post-magmatic metamorphism of ultrabasites. Sample collections are divided into three groups. 1. Oceanic peridotites from the rift zones of the mid-ocean ridges and transform faults. 2. Peridotites of the submarine ridge Gorringe, located within the Azoro-Gibraltar zone of faults. 3. Dunites of the Pekulney complex (Chukotka) formed in the island arc system. It has been established that in all selected regions, samples of serpentinized hyperbasites have high values of natural residual magnetization, magnetic susceptibility and saturation magnetization. The highest values of magnetic parameters are the dunites of the Pekulney complex. Estimation of the dependence of the concentration of ferrimagnetic materials C% of the degree of serpentinization of the SS%. showed that it is practically of little significance. The main factors contributing to the increase in the concentration of magnetite are the increased iron content of olivine in ultrabasites and the temperature of metamorphism. The question of the period of formation of magnetites and the stability of their primary residual magnetization requires further study.

Summary of heat flow studies in Nigeria

A traditional approach for heat flow determination requires two parameters. They are a geothermal gradient and heat conductivity of rocks comprising the considered depth interval. The geothermal gradient is determined from a thermogram recorded in a wellbore and the heat conductivity is obtained from the laboratory measurements of selected rock samp les. There are some variations of this approach to both get the gradient and heat conductivity values. However, there are many areas without boreholes to register their thermograms, or at least to have several temperature readings at intermediate positions of bottom holes and traditional methods of heat flow determinations cannot be used. Recently another method was proposed to estimate heat flow. It was derived from spectral analysis of magnetic field. During last years it was widely used in Nigeria for areas where deep boreholes are absent. It uses estimates of depths to the base and bottom of the causative body derived from analysis of the magnetic field maps. The base of the causative body corres ponds to the depth of the Curie surface at which rocks lose their magnetic properties. It is known that it happens at the temperature around 580 °C that slightly varies depending on the content of magnetite within the causative body. The temperature at the top of this body is estimated. The heat flow density can be calculated knowing the geothermal gradient within this depth interval and heat conductivity of rocks. A preliminary heat flow density map was compiled based on all accessible heat flow data. A comparison of heat flow data from several regions of the country, determined using both methods provides rather good agreement.

Iron deposits hosted by banded iron-formations in the Yilgarn Craton: Products of sequential iron enrichment by magmatic, marine and meteoric fluids

Mesoarchean Algoma-type BIF in the Yilgarn Craton are locally enriched by secondary processes to iron concentrations approaching 72 wt% Fe. While their near-surface goethite–hematite ores are unequivocally the product of supergene fluid alteration, their deeper magnetite and crystalline hematite–martite ores have a contentious origin. This study shows that magnetite ores formed after diagenesis and peak greenschist facies metamorphism of BIF, coinciding with regional deformation events. The ores formed by a multi-stage process involving initial replacement of primary quartz bands in BIF by hypogene carbonate minerals, followed by the dissolution of the carbonate and concentration of magnetite. At the Beebyn deposit, the earliest fluids were hot (~440 °C), CO2–vapor-rich, and were likely derived from felsic magmatic fluids. In contrast, the fluids responsible for carbonate alteration at the Matthew Ridge, Koolyanobbing, and Windarling deposits were cooler (366–125 °C) and aqueous-rich with salinities from 0.3 to 43.9 wt% NaCl equiv. Their Cl–Br and C–O isotopic ratios suggest they are the product of mixing between magmatic fluids and heated seawater. In all deposits, later cooling (~178–98 °C) of these fluids led to dissolution of carbonate minerals and concentration of magnetite. Dated monazite and xenotime from magnetite ores demonstrates that fluid alteration of BIF began in the Mesoarchean and continued episodically through to the Paleoproterozoic. Later specular hematite-rich veins that cut and modify magnetite ores crystallized from aqueous-rich fluids that are more oxidized, with salinities from 0 to 28.7 wt% NaCl equiv. and crystallization temperatures of 243–85 °C. Their Cl–Br and C–O isotopic fluid ratios indicate that they formed from mixing between heated seawater and meteoric waters. The BIF-hosted iron deposits in the Yilgarn Craton show remarkable similarities with the well-studied iron deposits in the Carajás Mineral Province and Hamersley Basin. They all show the same transition through time from magnetite- to hematite-rich ores. Subsequent episodic, tectonically-driven, fluid alteration events led to further iron enrichment in these deposits. The transition in ore types most likely corresponds to a common guiding process, namely the uplift of crustal rocks containing BIF – resulting in the progressive shallowing of fluid alteration pathways and the greater influence of cooler, more oxidized, hydrothermal fluids. Unlike iron deposits hosted by Algoma-type BIF in the Yilgarn and Carajás, iron deposits hosted by Superior-type BIF in the Hamersley Basin display a greater influence of oxidized marine and meteoric waters, without involvement of magmatic fluids.

Complexity of characterizing mafic-ultramafic remnants of Archean layered complexes in high-grade terranes: The scenario from Motloutse Complex, southwestern Zimbabwe craton

Mafic-to ultramafic-rocks of Archean layered complexes in high-grade terranes typically occur as inclusions closely associated with supracrustal rocks in granitoid gneiss. The reconstruction of the original stratigraphy and sequence of events related to Archean layered complexes is complicated by the fragmental occurrence and effect of overprint event(s). The case study presented here highlight these issues from the Motloutse Complex terrane, southwestern Zimbabwe Craton. Peridotite-pyroxenite and gabbro-leucogabbro-anorthosite form separate bodies closely associated with amphibolite in the Lechana area. They occur as inclusions within ∼2.65 Ga tonalite gneiss. Amphibolite is massive, has a stratiform occurrence and is folded, with gabbro-leucogabbro-anorthosite intruding along the fold limbs. Rare amphibolite xenoliths occur in gabbro-leucogabbro-anorthosite and peridotite-pyroxenite. Modal and cyclic layering is well preserved in the mafic and ultramafic intrusive bodies. Anatectic and alkali-metasomatic overprints, the later related to shear deformation, locally affected the Lechana rocks. The late stage events are contemporaneous and is dated by the ∼2.0 Ga (2013 ± 18 Ma) U-Pb zircon overgrowth age. Amphibolite exhibit prominent granoblastic polygonal fabric defined by amphibole-plagioclase. Gabbro-leucogabbro-anorthosite are locally gneissic. The different mafic rocks are variably affected by overprint events, and contain garnet related to anatectic overprint and epidote related to metasomatic overprint. Peridotite-pyroxenite exhibits no metamorphic re-equilibration textures, but are serpentinized and host widespread magnetite-rich layers. Amphibolite and associated gabbro have conspicuous sulphide concentration (up to 5 modal%), and include pyrrhotite, chalcopyrite (replaced by covellite), pyrite and pentlandite. No magnetite or sulphide concentration occur with leucogabbro-anorthosite. Whole-rock geochemical characteristics of the amphibolites are similar to tholeiitic basalts, but that of the peridotite-pyroxenite and gabbro-leucogabbro-anorthosite indicate different lineage. The suggested model considers amphibolite as a stratiform meta-basalt, which was folded during an earlier deformation event. Based on the presence of meta-basalt (amphibolite) roof pendants on top of both mafic and ultramafic intrusions, it is argued that the peridotite-pyroxenite and gabbro-leucogabbro-anorthosite were emplaced into Archean oceanic crust. The mafic-ultramafic intrusions could either be part of a single Mesoarchean layered complex or represent two different suites. In view of the restricted occurrence, lack of interlayering, different pyroxene affinities (clinopyroxene in gabbro and orthopyroxene in peridotite-pyroxenite) and wide compositional gap between mafic and ultramafic intrusions, we favour the later scenario. Peridotite-pyroxenite, interpreted as part of a Mesoarchean layered ultramafic complex, intruded the mafic volcanics. Layered gabbro-leucogabbro-anorthosite also intruded into the basaltic rock, separate from the ultramafic complex. The intrusion of protolith of the tonalite gneiss then dismembered the mafic and ultramafic sequences. The results of the present study highlight the need for detailed evaluation of spatially associated mafic-ultramafic rock remnants in high-grade terranes; they need not be genetically related but could be part of different magmatic episodes. Such exercise has implications in properly understanding the geodynamic setting of formation of these Archean upper mantle-derived rocks; the current arguments polarised between two end-member settings – plate margin versus intraplate setting.

Magnetic mineral dissolution recorded in a lacustrine sequence from the Heqing Basin, SW China, and its relationship with changes in the Indian monsoon

The dissolution of magnetic oxides is an important process in many lake environments. Understanding this phenomenon is crucial for the paleoenvironmental interpretation of the magnetic properties of lake sediments. In order to reveal its effects on sedimentary magnetic properties, and to assess the possible associated paleoenvironmental implications, we carried out detailed rock magnetic analyses of the selected samples from a 920-kyr lacustrine sequence from the Heqing Basin, SW China. The results indicate that the sedimentary magnetic properties are controlled by the concentration and grain size of magnetite and maghemite. High magnetic susceptibility (χ) intervals contain more fine-grained magnetite and maghemite, while low χ intervals contain only minor amounts of residual magnetite. The decreased content of fine-grained maghemite from high χ to low χ intervals reflects the dissolution of magnetic oxides during deposition. Intervals affected by strong magnetic dissolution have a high TOC content and correspond to times of high Antarctic temperatures, suggesting that magnetic mineral dissolution intensity was associated with variations in the strength of the Indian Summer Monsoon (ISM). Notably, the ISM is sensitive to Southern Hemisphere warming. Weak magnetic dissolution indicates a dry climate occurred since ~320 kyr in the Heqing Basin. This dry/cool event was widespread across the Eastern Bay of Bengal, Equatorial Indian Ocean and Northern Australia, and was linked to a strengthened Indian Ocean Dipole (IOD). Since the moisture source of the Heqing Basin was mainly from the above regions, we infer that the influence of the IOD extended northwards to SW China.

Variation of Iron Species in Plagioclase Crystals by X‐ray Absorption Fine Structure Analysis

AbstractSpeciation analysis of Fe in single plagioclase crystals separated from two different gabbros was performed to understand the crystallization mechanisms of magnetite exsolution. Iron species in single crystals were measured using Fe K‐ and LIII‐edge X‐ray absorption fine structure (XAFS) analysis. The K‐edge pre‐edge analysis showed variation in the averaged valence state of Fe in plagioclase crystals even if they had been separated from the same gabbro that was further confirmed by the LIII‐edge analysis. The K‐edge pre‐dedge analysis also suggests the various degrees of contribution from tetrahedral Fe. The mixing of tetrahedral and octahedral Fe leads to an underestimation of the averaged valence state of Fe for the K‐edge pre‐edge analysis; thus, we adopted the LIII‐edge result for the valence state of Fe in plagioclase crystals. Iron K‐edge extended XAFS (EXAFS) analysis of two plagioclase crystals separated from the same gabbro clearly showed different coordination environments. A weakening of EXAFS oscillation was recognized in one sample, because two Fe–O bonds (Fe3+–O1 and Fe2+–O2) cancelled out the oscillations of each other. The EXAFS spectrum of the other plagioclase crystal suggested a homogeneous distribution of Fe. The content of exsolved magnetite in these crystals is nearly identical, indicating that the exsolution of magnetite in plagioclase crystal had been completed before the temperature decrease that stopped the ordering of Fe ions in tetrahedral sites.

Effect of the Conditions the Reaction on the Formation of Iron Nanoparticles during the Reduction of Iron(III) Ions with Sodium Borohydride

Abstract—Iron nanoparticles are obtained by reducing iron(III) chloride with sodium borohydride in aqueous solutions at room temperature without using stabilizing agents. The obtained samples are characterized by X-ray diffraction analysis, low-temperature adsorption of argon, and transmission electron microscopy. The effect of the concentration of reagent solutions, the molar ratio of reagents, and exposure to ultrasound and inert atmosphere (Ar) on the size and composition of the resulting particles is found. Depending on the conditions of borohydride reduction of iron salts in an aqueous solution, both agglomerates of iron nanoparticles (5–50 nm) of 200 nm or larger and individual iron nanoparticles of 1 to 20 nm in size can be obtained. The presence and concentration of wustite and magnetite in the composition of the obtained particles mainly depend on the concentration of the reducing agent.

Determination of Optimum Production Parameters for Depletion of Balkhash Copper-Smelting Plant Dump Slags

Research is conducted on depletion of Vanyukov furnace (VF) slag of the Balkhash Copper Smelting Plant. It is proposed to carry out charge smelting and the depletion of slag in a two-zone VF furnace that has oxidizing and reducing zones separated by a partition. In order to determine the main production parameters of the operation of such a furnace laboratory studies are conducted making it possible to establish optimum conditions for smelting a copper charge. Optimum slag compositions are determined, slag obtained under oxidation and reduction conditions is studied thermogravimetrically, and the melting temperature is determined in each zone: 1285 and 1297 °C. It is established that a reduction in magnetite content to 2.0–2.3% makes it possible to reduce the copper content to 0.5–0.7% in dump slags.

High-performance fibre-reinforced heavyweight self-compacting concrete: Analysis of fresh and mechanical properties

Fibre-reinforcement of most of the concrete technologies, such as heavyweight concrete (HWC) and self-compacting concrete (SCC), would promote their practical applications through upgrading their mechanical properties, and subsequently, structural performance. This study evaluates the fresh and mechanical properties of fibre-reinforced heavyweight self-compacting concrete (FRHWSCC). Magnetite was used as heavyweight aggregate (HWA). Hooked-end steel and polypropylene (PP) fibres with length of 60 and 65 mm and diameter of 0.75 and 0.85 mm, respectively, were applied as reinforcements. Two different HWA content (75% and 100%), and four different volume fractions including 0.25%, 0.50%, 0.75%, 1.00% for steel, and 0.10%, 0.15%, 0.20%, 0.25% for PP fibres were utilized. To evaluate the fresh properties of FRHWSCC, slump flow test including slump flow diameter and T500mm, and J-Ring test have been performed. Hardened-state density, compressive, tensile, and flexural strength were measured to assess the mechanical properties of FRHWSCC. The obtained results for the fresh properties revealed that despite the negative impact of HWA and fibres on the workability of SCC, the FRHWSCC with both steel and PP fibres were still capable to retain their self-compacting characteristics according to the EFNARC standards. The hardened densities of specimens were above the density threshold for HWC, except for the FRHWSCC containing steel fibre, which showed slight decrease by increasing the steel fibre content to 0.5%, 0.75%, and 1.00% at 75% magnetite content, revealing the void formation within the cement paste. Compressive, tensile, and flexural strength results showed enhancement in the mechanical properties of FRHWSCC by increasing the fibre content, however, for both fibre types, increasing the HWA content impacted the mechanical properties in a negative manner, especially by aging the concrete. Finally, the load-deflection curves analysis confirmed the more ductile failure mode for the FRHWSCC comparing to plain SCC.

Surface photochemical studies of nano-hybrids of A3B porphyrins and Fe3O4 silica-coated nanoparticles

This study reports a surface photochemistry behaviour of two tetrapyrrolic structures: 5,10,15,20-tetra-(4-carboxymethylphenyl) porphyrin (P1.1) and 5-(4-hydroxy-3-methoxyphenyl)-10,15,20-tris-(4-carboxymethylphenyl) porphyrin (P1.2), covalently bound to silica-coated magnetite nanoparticles (Fe3O4@SiO2) imbibed into a polyethylene glycol (PEG) matrix and in the form of a fine powder. The initial compounds and the nano-hybrids imbibed in the PEG matrix were characterized using Fourier transformed infrared spectroscopy (FT-IR), diffuse reflectance absorption spectroscopy for ground state molecules (GSDR), X-ray diffaction (XRD), transmission electron electron microscopy (TEM) as well as several luminescence emission spectroscopies. The combined use of these methodologies enabled us to obtain a surface photochemistry characterization of these new nano-hybrid materials.For the powdered samples of P1.1 or P1.2 and Fe3O4@SiO2 imbibed into the powdered PEG a detailed absorption study and a correlation of fluorescence emission intensity with the magnetite concentration were performed. New covalent bonds porphyrin-Fe3O4@SiO2 were detected using FT-IR transmission spectra. A donor-acceptor interaction with change of the oxidation level of the porphyrins was also observed. Fluorescence emission quantum yields and lifetimes of the two porphyrins were determined for all samples and two populations of the porphyrin molecules exist, free porphyrin (unquenched) and porphyrin with Fe3O4@SiO2 NPs attached, the quenched porphyrin. In this way, the amount of the available excited porphyrin for singlet oxygen formation is reduced, therefore the presence of the Fe3O4@SiO2 NPs may not favor this specific PDT action by the Type II mechanism, but it prevents aggregation of the porphyrins, even when a PEG matrix is used, and Type I mechanisms remain active.