Iron Oxide Crystals Research Articles

A Microstructural and Compositional Study of ε-Fe2O3 Crystals in the Hare’s Fur Jian Ware

The Jian kilns in the present-day Jianyang County of Fujian Province are well known for their thick and lustrous black-glazed porcelain production. The hare’s fur (HF) glazed Jian wares characterized by radial fur-like strips, as one of the most typical representatives of black-glazed tea bowls, originate from phase separation of glaze melt and crystallization of iron oxides. In this study, various techniques were performed on the yellowish-brown HF samples, including portable energy-dispersive X-ray fluorescence (PXRF), synchrotron X-ray absorption near-edge spectroscopy (XANES), optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy (RS). The objective of this study was to well understand the microstructure characteristics and chemical compositions of glaze patterns. Results showed that the main constituents of the ceramic glaze were alumina (10.61–16.43 wt.%), silica (62.20–77.07 wt.%), calcium (3.85–6.97 wt.%), and iron oxide (4.10–8.35 wt.%). The studies provided evidence that metastable epsilon-iron oxide crystals (ε-Fe2O3) formed on the brownish-yellow glazed surface. Microstructural analysis revealed that there were three types of crystal structures in the glaze surface: One consisted of well-grown leaf-like or dendritic-like structure with highly ordered branches at micrometers scales; another comprised flower-like clusters accompanied by branches radiating from the center, petals growing along the branches, and needles on both sides of the petals; the last type involved a honeycomb structure tightly packed with plentiful spherical or irregular-shaped particles. In addition, ε-Fe2O3 crystals in the cross-section of the glaze showed a gradient distribution.

Production and characterization of porous magnetic biochar: before and after phosphate adsorption insights

AbstractThe modification process of biochars enables different advantages including enhanced adsorption properties for different pollutants. Herein, porous magnetic biochars (PMB) were successfully produced from softwood biomass through a two-step pyrolysis process together with FeCl3 modification. The effect of production temperature on adsorption was studied at 200 or 300 °C, followed by iron salt modification and subsequent pyrolysis at 600 or 800 °C. Biochars were characterized before and after phosphate adsorption via various characterization methods to acquire structural, elemental, and morphological properties of the adsorbent. The effects of phosphate concentration, contact time, and temperature on the adsorption process were examined in the batch mode. The characterization showed embedded iron oxide crystals of 23 nm within the biochar structure with a magnetic strength of 38.9 emu/g, which can assist the separation process of the powdered adsorbent from the aqueous medium. The surface area of the PMB was measured as 93 m2/g and 0.002 cm3/g pore volume. PMB showed complete removal (100%) of phosphate at the lower concentration (5 mg/l P). At higher concentration (25 mg/l P), the biochar prepared under 200/800 °C showed the highest removal (30%). The adsorption was enhanced with time (optimal 3 h) and temperature, which shows endothermic chemisorption following Langmuir isotherm and Pseudo-second order kinetic models. The desorption study suggested the slow release of phosphate from the spent adsorbent and potential reuse for soil enhancement. These results point towards the sustainable use of PMB as an effective and magnetically recyclable adsorbent for phosphate removal and reclaim.

Room-temperature atomic layer deposition of iron oxide using plasma excited humidified argon

Room-temperature atomic layer deposition (RT-ALD) of iron oxide is developed with a precursor of bis(N, N′-diisopropyl-propionamidinate)iron [(DIPPA)2Fe] and plasma excited humidified Ar. Saturated conditions of (DIPPA)2Fe and plasma excited humidified Ar exposures at room temperature (23–25 °C) are investigated by in situ IR absorption spectroscopy for finding the RT-ALD process condition. Using the designated process, the growth per cycle of the iron oxide RT-ALD is confirmed as 0.15 nm/cycle based on the film thicknesses measured by the spectroscopic ellipsometer. The x-ray photoelectron spectroscopy suggests that the stoichiometry of the deposited iron oxide is closed to that of Fe2O3. The grown film is composed of partly crystallized iron oxides, confirmed by cross-sectional TEM and AFM. The RT deposited iron oxide exhibits a magnetic volume susceptibility of 1.52, which implies the applicability of the present coating for magnetic drug delivery. We discuss the surface reaction with the IR absorption spectroscopy and the quartz crystal microbalance. The (DIPPA)2Fe molecule is suggested to adsorb on the Fe2O3 surface with mixed first- and second-order reactions at RT. It is also suggested that amidinate ligands in (DIPPA)2Fe are released in the course of the adsorption and the remaining ligands are oxidized by the plasma excited humidified Ar. The RT iron oxide deposition is demonstrated, and the reaction mechanism of room-temperature ALD is discussed in this paper.

Medium-range structure motifs of complex iron oxides

Natural occurring iron oxides, such as Fe2O3, Fe3O4, and FeO, are abundant on Earth's surface and feature many implications in our daily life since the Iron Age, the final epoch of the prehistory of humanity. The physics of iron oxides is at the frontier of physical research due to their complicated magnetic and electronic properties. What makes it even more intriguing is the introduction of pressure, which not only regulates the crystal structures and physical properties, but also creates new iron-oxide stoichiometry. Recent studies discovered several novel iron-oxygen compounds under various pressure–temperature conditions. Despite different Fe/O ratios, those iron oxides are built upon similar structural units including FeO6 octahedra and trigonal prisms. Complex stoichiometry of pressurized iron oxides is built up by stacking layers of those FeO6 units, and in the medium-range, they are organized by certain structural motifs. In this perspective, we go beyond conventional iron-oxygen binary compounds and reveal the general formation mechanism of complex iron oxide crystals under high-pressure conditions. The results will be helpful for summarizing literary works of iron oxides and exploring novel stoichiometry with optimal physical properties.

Characterization of material sintered from the final flotation waste and zeolitic tuff

The paper deals with the characteristics of synthesized glass-ceramics obtained by sintering a mixture of final flotation waste (FFW) with tuff at 1260?C for 7 h, followed by the annealing of pressed samples at 1080oC for 36 h. The experiments were done in order to find the possibility for the valorization of waste material (FFW). By thermal treatment of mixtures of T20 (20 % tuff, 80 % FFW) and T40 (40 % tuff, 60 % FFW) to a temperature of 1260oC over a period of 7 hours, is obtained glass-ceramics with dendritic structure. The synthesized glass-ceramics consists of two phases: iron oxide crystals (maghemite, magnetite, and hematite) and glass with an approximate ratio of phases 32/68 (T20) and 23/77 (T40), respectively. The relatively small shrinkage of the synthesized material (up to 7 %) enables reliable control when designing a given shape indicating that such glass-ceramics can be used as a basis for obtaining construction material. The synthesis of pressed samples of mixtures (T20 and T40) at 1080oC for 36 h produces glass-ceramics that have a high coefficient of sound attenuation, which indicates good acoustic insulating properties.

New Phenotype and Mineralization of Biogenic Iron Oxide in Magnetotactic Bacteria.

Many magnetotactic bacteria (MTB) biomineralize magnetite crystals that nucleate and grow inside intracellular membranous vesicles originating from invaginations of the cytoplasmic membrane. The crystals together with their surrounding membranes are referred to as magnetosomes. Magnetosome magnetite crystals nucleate and grow using iron transported inside the vesicle by specific proteins. Here, we tackle the question of the organization of magnetosomes, which are always described as constituted by linear chains of nanocrystals. In addition, it is commonly accepted that the iron oxide nanocrystals are in the magnetite-based phase. We show, in the case of a wild species of coccus-type bacterium, that there is a double organization of the magnetosomes, relatively perpendicular to each other, and that the nanocrystals are in fact maghemite. These findings were obtained, respectively, by using electron tomography of whole mounts of cells directly from the environment and high-resolution transmission electron microscopy and diffraction. Structure simulations were performed with the MacTempas software. This study opens new perspectives on the diversity of phenotypes within MTBs and allows to envisage other mechanisms of nucleation and formation of biogenic iron oxide crystals.

Angle dependence of Jian bowl color and its coloring mechanism

Jian bowl is generally known for its artistic appearance such as hare's fur and oil spots caused by the crystallization of iron oxides on the glaze surface. While very few Jian bowls have angle-dependent colors, scientific research on the topic is lacking owing to the scarcity of relevant samples. In this study, the angle-dependent colors of Jian bowls were systematically studied using various characterization techniques, such as angle-resolved reflectance spectra, X-ray diffraction, micro-Raman, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic force microscopy. The angle dependence phenomenon of Jian bowl colors was classified into two types, and the coloring mechanisms were clarified. The first type of coloring mechanism is assumed to be coherent light scattering by an amorphous photonic structure formed during the firing process, which has weak angle dependence. The second type of coloring mechanism is thin-film interference, which has obvious angle dependence and is closely related to the corrosion process of Jian bowls in the burial environment.

Preparation of copper ferrite by sol–gel method and the synergistic catalytic for the thermal decomposition of ammonium perchlorate

In the present work, copper ferrite was prepared by a simple and mild sol–gel method followed by low-temperature calcination, and characterized by various analytical techniques. The X-ray diffraction (XRD) analysis suggests that the copper ferrite with the spinel-type ferrite crystal forms have been successfully prepared. More crystal defects are observed in copper ferrite crystals than in the pure iron oxide and copper oxide crystals. The scanning electron microscopy (SEM) and nitrogen adsorption–desorption analyses reveal that the prepared copper ferrites are mesoporous structures with large specific surface areas and the specific surface area increases with the increase of Fe content. The effects of the structure of copper ferrite on its catalytic activity for the thermal decomposition of ammonium perchlorate (AP) and the catalytic mechanism were investigated and explored based on the thermogravimetric analysis of the decomposition process. It is found that the copper ferrites prepared at the molar ratios of Cu/Fe of 1/2 and 1/4 exhibit the best catalytic activities for the thermal decomposition of AP. The synergistic catalytic mechanism of Cu–Fe–O is proposed based on the electron transfer and proton transfer theories for the thermal decomposition of AP.

Induction of Axonal Outgrowth in Mouse Hippocampal Neurons via Bacterial Magnetosomes.

Magnetosomes are membrane-enclosed iron oxide crystals biosynthesized by magnetotactic bacteria. As the biomineralization of bacterial magnetosomes can be genetically controlled, they have become promising nanomaterials for bionanotechnological applications. In the present paper, we explore a novel application of magnetosomes as nanotool for manipulating axonal outgrowth via stretch-growth (SG). SG refers to the process of stimulation of axonal outgrowth through the application of mechanical forces. Thanks to their superior magnetic properties, magnetosomes have been used to magnetize mouse hippocampal neurons in order to stretch axons under the application of magnetic fields. We found that magnetosomes are avidly internalized by cells. They adhere to the cell membrane, are quickly internalized, and slowly degrade after a few days from the internalization process. Our data show that bacterial magnetosomes are more efficient than synthetic iron oxide nanoparticles in stimulating axonal outgrowth via SG.

Fractionation of some natural radionuclides in Albic Retisol

In the present work, the fractionation of heavy natural radionuclides was investigated in Albic Retisol in the Moscow region of Russia. Fractionation was performed using the Pavlotskaya method. 238U and 232Тh were measured via inductively coupled plasma mass spectrometry and 226Ra was measured using an alpha-radiometer that considered the decay of Ra isotopes and accumulation of the resulting decay-related products. Results showed that the potential mobility of radionuclides during migration to adjacent environments and biological availability to plants follows the order 226Ra >238U > 232Тh. The depletion of 226Ra in the humus horizon A was manifested as a decrease in the 226Ra/238U activity ratio to below 1 in fraction F4.1 (associated with organic matter) and fraction F4.2 (acid-soluble compounds). The profile distribution of 226Ra and 238U in the residual fraction revealed the genetic relationship between these radionuclides. Mobile compounds of 238U and 232Th leached into the lower part of the profile where they became fixed, mainly as the components of fractions associated with organic matter and crystallized iron oxides. A similar profile distribution was found for 238U, 232Тh, and Fe in the acid-soluble fraction associated with crystallized iron oxides. The results obtained herein can form the basis for regulating the mobility and bioavailability of radionuclides to ameliorate their adverse effects on plants and soil ecosystems.

Microstructure and coloring mechanism of iron spots on bluish white porcelain from Jingdezhen of the Song Dynasty

Jingdezhen is famous for its bluish white (Qingbai) porcelains of the Song Dynasty, and those decorated with iron spots are distinctive among them. Herein, iron spots on a bluish white porcelain were investigated using a series of microscopic and spectroscopic characterizations. We found the decreasing iron content from more than 8 wt% to about 2 wt% during the glaze color transition from rusty to brown and finally into green, which built a connection on the coloring mechanism of iron-rich crystallized glaze and celadon glaze. We identified the rare ε-Fe2O3, a promising magnetic material, in both the dark brown crystals and the triangular crystals in the rusty area, which is its first discovery among bluish white porcelains. Based on these findings, we discussed the coloring mechanism of iron-spot decoration along with the physical form of the iron oxide crystals, indicating the partially reducing atmosphere during firing process.

Формы железа в почвах естественных ландшафтов Верхнего Приангарья

Iron occupies one of the leading places among other elements in terms of content in soils and, having the ability to change valence and properties, diagnoses the typical and sub-type features of many soils, and most importantly, the direction of the soil formation process. Gypsum-bearing soils are formed on the deluvium of the Cambrian sedimentary rocks, in conditions of a hilly-flat relief, caused by water-erosion processes that have created surface dissections by numerous valleys and hollows. Gypsum-bearing soils are located on the elevated parts of the relief of the first floodplain river terraces, as well as in the lower parts of the relief and in river valleys. The climatic conditions of soil formation can be classified as arid. The amount of precipitation in the study area is much less than evaporation. The content, composition, and ratios of various forms of iron and the profile distribution of soils formed on gypsum-bearing red-colored Cambrian sedimentary rocks of the Upper Angara region were studied. For this, the composition of the soil cover in the landscape under study and the soilforming processes taking place in the soils were determined: brown arid calcareous soils are formed in the southern exposure of the slopes; in the northern exposure - chernozems, chernozems and meadow soils. An important morphoanalytical feature of soils is the presence of significant amounts of gypsum and carbonates in the profile. The leading soil-forming process in the landscape is the process of humus accumulation, which is clearly manifested in soils on the slopes of the left bank of the Zalari River. The group composition of iron was determined by analytical methods. The ratios of various iron groups, which are characteristic of landscape soils, and the regularities of the distribution of groups in soil profiles have been established. It was revealed that the degree of ferruginization of the soils of the left bank is in moderately low and very low limits; the degree of ferruginization of soils on the right bank is moderately low. The iron groups in the profiles are poorly differentiated. Silicate iron prevails over non-silicate. The significant predominance of silicate forms of iron over non-silicate forms indicates a low intensity and weak development of weathering processes. In all soils of the landscape, only traces of amorphous iron are determined. The mobility of iron in the soils of the landscape is practically absent, due to the insufficient amount of the amorphous form. In all landscape soils, the degree of oxidogenesis is very low. Crystallization of free iron oxides and hydroxides does not occur due to their absence.

Nanometer scale insight on the analysis of limpets mineralized teeth: Special focus on the silica-containing regions

We report the electron microscopy-based analysis of the major lateral tooth of the limpet Colisella subrugosa during early and intermediate stages of development. We aimed to analyze the structural relationship among the needle-like crystals of the iron oxide goethite, the amorphous silica phase that forms the tooth base and occupy inter-crystalline spaces in the cusp, and the chitin fibers of the matrix. Goethite crystals followed the three dimensional organization pattern of the chitin fibers in the cusp. In the tooth base, spherical individual silica granules were found in regions where the chitin fibers cross. The spherical granules near the interface between the tooth base and the cusp (junction zone) formed an almost continuous medium that could easily be ultrathin-sectioned for further analysis. By contrast, the nearby silica-rich region localized on the other side of the junction zone contained needle-like goethite crystals immersed in the matrix and presented a conchoidal fracture. The chitin fibers from the silica granules of the tooth base were dotted or undulating in projection with a periodicity of about 6 nm when observed by high magnification transmission electron microscopy. Very thin goethite crystals were present in the base of the cusp near the junction zone surrounded by silica. On several occasions, crystals presented internal thin straight white lines parallel to the major axis, indicating a possible growth around fibers. We propose that silica and iron oxide phases mineralization may occur simultaneously at least for some period and that silica moderates the dimensions of the iron oxide crystals.

Improvement of Oxygen Mobility with the Formation of Defects in the Crystal Structure of Red Mud as an Oxygen Carrier for Chemical Looping Combustion.

Fe₂O₃ is the major component of red mud, which is a by-produced after eluting aluminum from bauxite in the Bayer process, and can be used as an oxygen carrier. On the other hand, red mud is unsuitable for using oxygen in the crystal lattice because of its low surface area. In this study the red-mud sample was sulfidated at high temperatures to improve the lattice oxygen mobility by forming lattice defects in the iron oxide crystals. To form crystal defects on red mud, iron oxide was converted to iron sulfide with hydrogen sulfide, and then re-oxidized by air to remove the sulfur components. In these processes, it was possible to generate defects could be generated in the crystal structure. Crystal defects are formed by the difference in the molar volume of oxygen and sulfur bound to the metal in the oxidation-sulfidation process. The surface area of the defective red mud increased from approximately 25.9 m₂/g to 122.1 m₂/g, and the pore volume increased from 0.1714cc/g to 0.2803 cc/g. In addition, the formation of crystal defects increased the oxygen transfer capacity of red mud from 1.75% to 2.25% at 15 vol.% hydrogen. This means that the amount of oxygen transported during the reduction process could be enhanced approximately 1.29 fold.

Role of Water in Phase Transformations and Crystallization of Ferrihydrite and Hematite.

The oxides, hydroxides, and oxo-hydroxides of iron belong to the most abundant materials on earth. They also feature a wide range of practical applications. In many environments, they can undergo facile phase transformations and crystallization processes. Water appears to play a critical role in many of these processes. Despite numerous attempts, the role of water has not been fully revealed yet. We present a new approach to study the influence of water in the crystallization and phase transformations of iron oxides. The approach employs model-type iron oxide films that comprise a defined homogeneous nanostructure. The films are exposed to air containing different amounts of water reaching up to pressures of 10 bar. Ex situ analysis via scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and X-ray diffraction is combined with operando near-ambient pressure X-ray photoelectron spectroscopy to follow water-induced changes in hematite and ferrihydrite. Water proves to be critical for the nucleation of hematite domains in ferrihydrite, the resulting crystallite orientation, and the underlying crystallization mechanism.

Crystal phase determined Fe active sites on Fe2O3 (γ- and α-Fe2O3) yolk-shell microspheres and their phase dependent electrocatalytic oxygen evolution reaction

Transition metal oxide nanomaterials have been extensively applied to the field of oxygen evolution reaction (OER), but few works have been studied to demonstrate the relationship between their crystal phases and OER performance. Herein, we compare the OER performance of the two different crystal phase iron oxide (α-Fe2O3 and γ-Fe2O3). The iron oxide yolk-shell microspheres were facile realized via one-step solvothermal method and the subsequent annealing treatment. An interesting phenomenon is present that α-Fe2O3 yolk-shell microspheres with a smaller specific surface area have better OER performance than that of γ-Fe2O3 yolk-shell microspheres. The crystal structure and X-ray photoelectron spectroscopy (XPS) results show that α-Fe2O3 yolk-shell microspheres have better electrocatalytic activity, which is due to the presence of more Fe active sites (Fe3+) exposured on the surface. These Fe active sites are beneficial to enhance the adsorption of hydroxyl groups in water molecules, leading to a higher OER performance. As an application example, the Fe2O3 yolk-shell microspheres are employed as an efficient OER electrocatalyst, showing the interdependence between phase and OER behavior.

Effect of lattice mismatch on magnetic properties of acicular spinel iron oxide particles with crystallized cobalt ferrite layer

Cobalt ferrite was epitaxially crystallized on acicular seed iron oxide particles with different lattice constants and same particle shape to analyze the effect of the lattice mismatch on magnetic properties. The coercive force obtained by crystallizing 27 vol% of cobalt ferrite was approximately 530–640 kA/m, which tended to increase with the decrease in the difference of lattice constants between the seed particles and cobalt ferrite, which is different from the results for thin films. The obtained coercive force was higher than that considering the contribution of anisotropy from the cobalt ferrite crystallized on the seed particles. In the acicular iron oxide spinel particles, the epitaxial growth of cobalt ferrite was considered likely to occur with a smaller difference in the lattice constants of the seed particles and cobalt ferrite. The high coercive force of the cobalt ferrite crystallized iron oxide particles strongly suggested the influence of exchange coupling between the seed iron oxide particles and cobalt ferrite layer.

Effects of sodium nitrate and heat treatment atmosphere on the synthesis of α–NaFeO2 layered oxide

α-NaFeO2 type layered oxides shows reversible intercalation/de-intercalation of sodium ions between the oxide layers, which is suitable as regenerable CO2 absorber and cathode material for secondary batteries. This paper reports a critical effect of heating atmosphere to synthesize pure α-NaFeO2 from equimolar sodium nitrate and iron oxide. Reaction of NaNO3 with γ-Fe2O3 was much faster in nitrogen than oxygen atmosphere and high-purity α-NaFeO2 was yielded in a few hours of heat treatment in nitrogen while in oxygen atmosphere the reaction was sluggish, resulting in partially sodiated γ-Fe2O3. Inert atmosphere thermodynamically enhances nitrate decomposition, which controls the reaction rate of NaNO3 with γ-Fe2O3, and increases the solubility of γ-Fe2O3 in molten NaNO3 to promote topotactic phase transformation to α-NaFeO2. Molten NaNO3 works as a solvent for ferric ions and a redox buffer for maintaining the lattice oxygen structure and oxidation state of γ-Fe2O3. Larger iron oxide crystal was found to be suitable for production of high-purity α-NaFeO2 in a wide temperature range.

Nitrate Reduction of the Siilinjärvi/Finland Mine Water with Zero-valent Iron and Iron Waste as Alternative Iron Sources

Nitrate reduction was optimized in water from the Siilinjarvi/Finland mine site with iron powder and iron nanoparticles. Iron waste from a mold machining industry was then tested as a potential alternative. Complete reduction of nitrate from the mine water was achieved with the iron powder and nanoparticles at pH 2. The iron waste, though less efficient, still achieved 53% nitrate reduction. Examination of the surface of the iron powder and waste by SEM–EDS showed iron corrosion: crystals of iron oxides grew on the iron surface as the pH increased during NO3− reduction, until about pH 5. The major by-product of the NO3− reduction of mine water was NH4+, with low NO2− concentrations (< 7%). Although iron powder and nanoparticles were more reactive, the iron waste results are promising. Despite its low BET surface area, the use of iron waste to treat high volumes of mine water would appear to have economical and sustainable advantages. More efficient NO3− reduction could possibly be attained with iron waste of higher BET surface area and/or by combining it with other chemical treatments.

Combined Haber-Weiss and vacancy mechanism: Ce4+ used as intelligent isomorphic ions in iron oxides

Cerium is known for its good ability to transition between the Ce3+ and Ce4+ forms, which modulates its ability to incorporate oxygen into different material structures. Therefore to promote the slow phase characterize by oxidative processes, related to phase of regenerating the reduced metallic sites, iron oxide-based catalysts partially replaced by cerium were synthesized, and their physical, textural and morphological properties were evaluated. The catalysts were prepared by synthesizing the magnetite phase and doping with cerium (Ce4+), such that the isomorphic ion content in the FeCex formula was 0.05> x> 0.2 mol. The X-ray diffraction (XRD) results of the oxide after Ce was incorporated exhibited peaks corresponding to magnetite, which is less crystalline than bulk iron, suggesting that the isomorphic ion was incorporated into the iron oxide crystal lattice. Furthermore, incorporating the rare earth element also favored the appearance of diffraction peaks corresponding to the formation of other iron phases, such as goethite. The results suggest a strong interaction between the metals, because even after the single addition of Ce4+, X-ray photoelectron spectrometry (XPS) analysis shows the presence of the +3 and +4 oxidation states. The materials obtained after incorporating cerium had a high catalytic capacity for removing a reactive red dye. The dye removal was significant, and the materials demonstrated a remarkable chemical stability and remained active for seven consecutive reaction cycles without the need for regenerating the active centers. The dye removal essentially occurs by a heterogeneous process, in which the active phase leaching rates are not significant.