Hematite Samples Research Articles

Top-down synthesis of mesocrystalline α-Fe2O3 submillimeter-sized rhombohedrons

ABSTRACTHere, we focus on the obtaining of mesocrystalline submillimeter-sized (150/50 µm) rhombohedral hematite (α-Fe2O3) by thermal treatment in air of single crystalline submillimeter-sized (150/50 µm) rhombohedrons of ferrous carbonate (FeCO3). Mass spectrometer-coupled thermogravimetric analysis and TGA-MS revealed the chemical reactions occurring during the thermal treatment of ferrous carbonate sample. The X-ray Diffraction (XRD) data sustain that the final product is hematite. The XRD line-profile analysis indicates that the resulted hematite is built of individual ordered crystallites with 66 ± 5 nm average sizes, confirmed by scanning electron microscopy and transmission electron microscopy images. Small-angle x-ray scattering investigation of hematite sample was presented. The log-log plot of scattering intensity decay showed the same slope, α = −3.76, corresponding to both high and low scattering vector regions; the fractal surface is Ds = 2.24. This fractality is extended over a range of sizes and can touch high molecular dimensionality. The internal morphology and the synthesis mechanism of the obtained hierarchical superstructure were described.

Revealing the Role of TiO2 Surface Treatment of Hematite Nanorods Photoanodes for Solar Water Splitting.

Ultrathin TiO2 is deposited on conventional hydrothermal grown hematite nanorod arrays by atomic layer deposition (ALD). Significant photoelectrochemical water oxidation performance improvement is observed when the ALD TiO2-treated samples are annealed at 650 °C or higher temperatures. The electrochemical impedance spectroscopy (EIS) study shows a surface trap-mediated charge transfer process exists at the hematite-electrolyte interface. Thus, one possible reason for the improvement could be the increased surface states at the hematite surface, which leads to better charge separation, less electron-hole recombination, and hence, greater improvement of photocurrent. Our Raman study shows the increase in surface defects on the ALD TiO2-coated hematite sample after being annealed at 650 °C or higher temperatures. A photocurrent of 1.9 mA cm(-2) at 1.23 V (vs RHE) with a maximum of 2.5 mA cm(-2) at 1.8 V (vs RHE) in 1 M NaOH under AM 1.5 simulated solar illumination is achieved in optimized deposition and annealing conditions.

SORPTION OF COPPER AND ZINC BY GOETHITE AND HEMATITE

<p>In the present work, the abilities of natural and synthetic samples of goethite and hematite to remove copper Cu(II) ) and zinc Zn(II) ions from aqueous solutions were compared. Batch adsorption experiments were performed in order to evaluate the removal efficiency of iron oxide samples. The effect of initial metal ion concentration, initial pH and time on adsorption of copper and zinc onto the iron oxides has been studied. The sorption data were represented by the linearized Langmuir model. Comparing the values of adsorption capacities, there were differences between the natural and synthetic samples, natural and synthetic goethite had higher sorption capacity for both metals than hematite. The copper ions showed higher affinity than zinc ions to all samples.</p>

Fixed bed reduction of hematite under alternating reduction and oxidation cycles

Abstract The rate of the reduction reaction of a low cost natural hematite oxygen carrier for chemical looping combustion was investigated in a fixed bed reactor where hematite samples of about 1 kg were exposed to a flowing stream of methane and argon. The investigation aims to develop understanding of the factors that govern the rate of reduction with in larger reactors as compared to mostly TGA investigations in the literature. A comparison of the experimental data with a model indicated that reaction between the methane and the iron oxide shows multi-step reactions. The analysis also shows that the conversion occurs with a process that likely consumes all the oxygen close to the surface of the hematite particles and another process that is likely controlled by the diffusion of oxygen to the surface of the particles. Additional analysis shows that the thickness of the fast layer is on the order of 8 unit crystals. This is only about 0.4% of the hematite; however, it comprises about 20–25% of the conversion for the 10 min reduction cycle.

Tailored properties of hematite particles with different size and shape

Red cubic and spherical hematite red cool pigments of different particle size were synthesized following two different methods. Cubic and spherical particles with larger particle sizes were obtained through a gel–sol method using chloride and nitrilotriacetate ions as shape controllers, and changing the starting temperature to control the final particles size. Smaller spherical particles were synthesized more rapidly following a catalytic phase transformation method in which the size control is obtained by varying the reagent concentration. Cool properties for the obtained particles were evaluated by calculating the solar reflectance for all hematite samples. The cool properties differ depending on the particle size and shape. By controlling the final size and morphology of pigment particles it is possible to obtain pigments with the desired cool properties. Pigment color properties were also evaluated using CIE XYZ and CIE xyY color spaces.

A Study of Rock Magnetism of High-Grade Hematite Ores

Rock magnetism is useful in various applications. Hematite is one of the two most important carriers of magnetism in the natural world and its magnetic features were mostly studied through laboratory experiments using synthetic hematite samples. A gap exists between the magnetic behaviors of hematite contained in the natural rocks and ores and those of synthetic hematite samples. This paper presents the results of a rock magnetism study on the natural hematite ores from the Whaleback mine in the Hamersley Province in the northwest of Western Australia. It was found that high-grade hematite ores carry a much higher remanent magnetization than induced magnetization. Hematite ores with less than 0.1% magnetite appear to have an exponential correlation between the bulk susceptibility and hematite content in weight percentage, different from the commonly accepted linear relationship between the bulk susceptibility and hematite content obtained from synthetic hematite samples. The new knowledge gained from this study contributes to a better understanding of magnetic behaviors of hematite, particularly natural hematite, and hence applications to other relevant disciplines.

Comparison of the Microwave Absorption Characteristics of Hematite, Magnetite and Pyrite

We provide an understanding of the microwave absorption characteristics of hematite, magnetite and pyrite by measuring and comparing the microwave heating rate, dielectric and magnetic properties and the absorbed microwave energy. The three methods have their own advantages and disadvantages, and supplement each other. Magnetite showed the strongest microwave absorption and rapid heating rate because of its dielectric and magnetic losses. Dielectric properties and calorimetry indicate that two pyrite samples had different microwave absorption characteristics, but a similar heating rate. Three types of hematite had a significant difference in interaction with the microwave. The heating rate of one of the hematite samples was most rapid and the sample had a higher dielectric loss factor. The ability of these minerals to absorb microwaves was maintained at a certain level when the microwave power and microwave heating time increased. For microwave-sensitive materials, the amount of absorbed microwave energy increased significantly with their mass.

Full vector low‐temperature magnetic measurements of geologic materials

AbstractThe magnetic properties of geologic materials offer insights into an enormous range of important geophysical phenomena ranging from inner core dynamics to paleoclimate. Often it is the low‐temperature behavior (<300 K) of magnetic minerals that provides the most useful and highest sensitivity information for a given problem. Conventional measurements of low‐temperature remanence are typically conducted on instruments that are limited to measuring one single‐axis component of the magnetization vector and are optimized for measurements in strong fields. These instrumental limitations have prevented fully optimized applications and have motivated the development of a low‐temperature probe that can be used for low‐temperature remanence measurements between 17 and 300 K along three orthogonal axes using a standard 2G Enterprises SQuID rock magnetometer. In this contribution, we describe the design and implementation of this instrument and present data from five case studies that demonstrate the probe's considerable potential for future research: a polycrystalline hematite sample, a polycrystalline hematite and magnetite mixture, a single crystal of magnetite, a single crystal of pyrrhotite, and samples of Umkondo Large Igneous Province diabase sills.

Beneficiation of Micaceous Iron Oxide from Veldurthi Area, Kurnool, AP,India

A micaceous hematite sample from Krishnapuram village, Veldurthi Mandal, Kurnool district, Andhra Pradesh was received for process evolution studies to obtain coating - welding rod - concentrate, assaying Fe>65%, SiO2 63%, SiO2 10000 gauss intensity produced a concentrate assaying 65.29% Fe, 4.07% SiO2, 0.42% Al2O3 and 0.32% LOI with 76.8% Fe distribution at wt% yield of 62.1, meeting pellet grade specifications. The above rougher concentrate after one cleaner WHIMS at >8500 gauss, assayed 67.80% Fe, 1.90% SiO2, 0.32% Al2O3, 0.22% LOI and 5 specific gravity with 63.6% Fe distribution at wt% yield of 50.0 meeting the specification of coating and welding rod industry.

Hematite and Mn oxide (U-Th)/He dates from the Buckskin-Rawhide detachment system, western Arizona: Gaining insights into hematite (U-Th)/He systematics

In this paper, we use several analytical methods in an effort to better understand the systematics of the (U-Th)/He chronometer in hematite and manganese oxides. 4He diffusion data from a polycrystalline hematite sample is consistent with diffusion from hematite crystals with a range of sizes similar to those directly observed in sample material. Combined with a compilation of hematite He diffusion data from previous studies, this supports the interpretation that in general crystal size is a primary control on He retentivity in hematite. 4He/3He diffusion data from a single fragment of a larger hematite crystal imply the presence of multiple diffusion domains smaller than the observed size of the crystal fragment, which may be related to cracks, inclusions, or other internal features, as well as higher concentrations of 4He in smaller domains. We use kinetic values determined in this and other studies and measurements of hematite crystal size in each dated sample to estimate approximate closure temperatures for each sample, most of which range from 140 to 240 °C. Relationships between minor element and parent nuclide concentrations and (U-Th)/He dates measured in aliquots of some analyzed hematite samples suggest that, in some cases, U and Th are concentrated in interstitial phases other than hematite. We identify two processes responsible for much of the dispersion in hematite dates from single samples. Removal of U- and Th-rich interstitial phases from analyzed material during sample preparation or analysis leaves behind unsupported 4He implanted in hematite crystals. This removal results in apparent (U-Th)/He dates artificially older than the time of hematite He closure. A smaller source of dispersion that is likely to still be significant in some samples can be attributed to the high He diffusivities of observed interstitial phases, which do not retain implanted He. (U-Th)/He dating of hematite from upper and lower-plate rocks in the Buckskin and Rawhide detachment fault system of western Arizona yields ages that coincide with the timing of rapid extension along the detachment fault. Comparisons of estimated hematite closure temperatures and hematite sample ages to data from other studies of the Buckskin-Rawhide detachment system lead us to conclude that hematite dates record rapid cooling that followed detachment zone mineralization. Mn oxide (U-Th)/He dates are interpreted as formation ages of minerals formed by hydrothermal fluids that circulated through upper-plate rocks after cessation of extension along the detachment fault. Overall, we find that (U-Th)/He dating of hematite and Mn oxide minerals are promising methods for obtaining temporal information about the formation and cooling of these common secondary phases.

Effect of solvent surface tension on the radius of hematite nanoparticles

In this work, the hematite (Fe2O3) nanoparticles were synthesized by homogeneous precipitation in alcohol (tert-butanol)/water mixed solvents with varied surface tension. The surface tension of the solvent was decreased from 55.8 to 15.9 mN m−1 by the increasing of the alcohol content from 20 to 80 vol %. The size of the particles was determined by BET, XRD and TEM techniques. Based on XRD results, the crystalline phase of Fe2O3 in all samples was attributed to the cubic hematite structure. The results show that the average particle size of the prepared hematite samples is decreased from 38 to 14 nm upon decreasing surface tension from 55.8 to 15.9 mN m−1.

Modification of Hematite Electronic Properties with Trimethyl Aluminum to Enhance the Efficiency of Photoelectrodes.

The electronic properties of hematite were investigated by means of synchrotron radiation photoemission (SR-PES) and X-ray absorption spectroscopy (XAS). Hematite samples were exposed to trimethyl aluminum (TMA) pulses, a widely used Al-precursor for the atomic layer deposition (ALD) of Al2O3. SR-PES and XAS showed that the electronic properties of hematite were modified by the interaction with TMA. In particular, the hybridization of O 2p states with Fe 3d and Fe 4s4p changed upon TMA pulses due to electron inclusion as polarons. The change of hybridization correlates with an enhancement of the photocurrent density due to water oxidation for the hematite electrodes. Such an enhancement has been associated with an improvement in charge carrier transport. Our findings open new perspectives for the understanding and utilization of electrode modifications by very thin ALD films and show that the interactions between metal precursors and substrates seem to be important factors in defining their electronic and photoelectrocatalytic properties.

An investigation of reaction parameters on geochemical storage of non-pure CO2 streams in iron oxide-bearing formations

Hematite deposit that is the main FeIII-bearing mineral in sedimentary red beds was proposed as a potential host repository for converting CO2 into carbonate minerals such as siderite (FeCO3), when CO2–SO2 gas mixtures are co-injected. This work investigated CO2 mineral trapping using hematite and sensitivity of the reactive systems to different parameters, including particle size, gas composition, temperature, pressure, and solid-to-liquid ratio. Experimental and modelling studies of hydrothermal experiments were conducted, which emulated a CO2 sequestration scenario by injecting CO2–SO2 gas streams into a NaCl–NaOH brine hosted in iron oxide-containing aquifer. This study provides novel information on the mineralogical changes and fluid chemistry derived from the co-injection of CO2–SO2 gas mixtures in hematite deposit. It can be concluded that the amount of siderite precipitate depends primarily on the SO2 content of the gas stream. Increasing SO2 content in the system could promote the reduction of Fe3+ from the hematite sample to Fe2+, which will be further available for its precipitation as siderite. Moreover, siderite precipitation is enhanced at low temperatures and high pressures. The influence of the solid to liquid ratio on the overall carbonation reaction suggests that the conversion increases if the system becomes more diluted.

Improvement of Hematite as Photocatalyst by Doping with Tantalum

The use of tantalum as a highly effective dopant for hematite photoelectrochemistry (PEC) has shown contradictory results in previous reports. We show here through screening of different compositions by scanning electrochemical microscopy that Ta doping significantly improves the PEC performance of dropcast films on fluorine-doped tin oxide (FTO). In studies with larger electrodes, a 2% Ta-doped hematite photoanode fabricated at 500 °C shows the highest improvement of photoactivity, which is ∼32 times higher than pure hematite even under visible light. At fabrication temperature higher than 500 °C (e.g., 600, 680 °C), the substrate FTO becomes more resistive and the dopant Ta prefers to segregate from the bulk phase (α-Fe2O3) and forms tantalum fluoride oxide (TaO2F), which may act as charge-carrier recombination centers, and the corresponding Ta-doped samples show much lower photoactivities. Ta-doped hematite samples show stronger (110) diffraction as compared with the pure α-Fe2O3. We show that the doping of Ta induced a preferential growth along the {001} basal plane, which has been reported to have good conductivity. We found the conductivity of the Ta-doped hematite was improved up to at least about one order of magnitude after the incorporation of Ta, with the improved carrier mobility decreasing recombination of the photogenerated holes and electrons.

Low‐Temperature Activation of Hematite Nanowires for Photoelectrochemical Water Oxidation

Hematite (α-Fe2 O3 ) nanostructures have been extensively studied as photoanode materials for photoelectrochemical (PEC) water oxidation. However, the photoactivity of pristine hematite nanostructures is fairly low and typically requires thermal activation at temperature of 650 °C or above. Here, we report a new method for enhancing the photocurrent of hematite nanowires at a substantially lower temperature of 350 °C by means of a two-step annealing process (activation process). Hydrothermally grown β-FeOOH nanowires were first annealed in a pure N2 environment at 350 °C to form magnetite, followed by partial oxidation in air to convert magnetite to hematite. During this process, Fe(2+) sites (oxygen vacancies) were intentionally created to increase the donor density and therefore the electrical conductivity of hematite. The oxygen-deficient hematite nanowire photoanode created at low temperature (350 °C) show considerably enhanced photoactivity compared to pristine hematite sample that prepared by thermal annealing of β-FeOOH nanowires at 550 °C in air. Moreover, this low-temperature annealing method can be coupled with an element doping method to further increase the photoactivity of hematite nanowire. Sn-doped hematite nanowires prepared by the same low-temperature annealing method show at least three fold enhanced photocurrent compared to the undoped sample. Significantly, the highest temperature in the entire annealing process was 350 °C, which is the lowest activation temperature ever reported for hematite nanowire photoanodes.

Magnetic properties of nano-scale hematite, α-Fe2O3, studied by time-of-flight inelastic neutron spectroscopy.

Samples of nanoscale hematite, α-Fe2O3, with different surface geometries and properties have been studied with inelastic time-of-flight neutron scattering. The 15 nm diameter nanoparticles previously shown to have two collective magnetic excitation modes in separate triple-axis neutron scattering studies have been studied in further detail using the advantage of a large detector area, high resolution, and large energy transfer range of the IN5 TOF spectrometer. A mesoporous hematite sample has also been studied, showing similarities to that of the nanoparticle sample and bulk α-Fe2O3. Analysis of these modes provides temperature dependence of the magnetic anisotropy coefficient along the c-axis, κ1. This is shown to remain negative throughout the temperature range studied in both samples, providing an explanation for the previously observed suppression of the Morin transition in the mesoporous material. The values of this anisotropy coefficient are found to lie between those of bulk and nano-particulate samples, showing the hybrid nature of the mesoporous 3-dimensional structure.

Cathodic shift of onset potential for water oxidation on a Ti4+doped Fe2O3photoanode by suppressing the back reaction

We present a surface corrosion method to shift the photocurrent onset potential cathodically for water oxidation on a Ti4+ doped Fe2O3 by about 100 mV. After the surface treatment, the doped hematite photoanodes showed a similar photocurrent onset potential to the lowest values obtained by loading with electrocatalysts or depositing functional over-layers. Moreover, the cathodic shift of the onset potential was preserved well even after a long operating time. The results indicated the effectiveness of this simple surface treatment. In order to make clear the reason for the onset potential shift, the doped hematite samples before and after surface corrosion were investigated by SEM, X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICP-MS), photoluminescence spectroscopy (PL), electrochemical impedance spectroscopy (EIS), Mott–Schottky and so on. Based on the experimental evidence, we proposed a new mechanism for the onset potential shift. The cathodic shift of the onset potential was due to decreasing the back reaction, but not accelerating water oxidation kinetics, passivating surface states or ions adsorption as reported in the previous studies. This strategy of suppressing the back reaction can offer a reference to reduce the overpotential for other photoelectrodes.

Adsorption of Cr (VI) on synthetic hematite (α-Fe2O3) nanoparticles of different morphologies

The adsorption of Cr (VI) from aqueous solution onto nanoparticles hematite (α-Fe2O3) of different morphologies synthesized by acid hydrolysis, transformation of ferrihydrite, sol gel methods has been investigated. The hematite particle sizes were in the range 15.69-85.84 nm and exhibiting different morphologies such as hexagonal, plate-like, nano-cubes, sub-rounded and spherical. The maximum adsorption capacity of Cr (VI) was found to be in the range 6.33–200 mgg−1 for all hematite samples. The kinetics of sorption was rapid, reaching equilibrium at 45–240 minutes. Sorption kinetics and equilibria followed pseudo-second order and Langmuir adsorption isotherm models. The rate constants were in the range 0.996–2.37×10−2 g/mg/min for all samples. The maximum adsorption was attained at pH 3.0, while adsorption decreased as the pH increased from pH 3.0 to 10.0. The study revealed that the hematite with plate-like morphology has the highest adsorption capacity. The sorption process has been found to be feasible following a chemisorption process, and adsorption of Cr (VI) onto hematite nanoparticles was by inner sphere surface complexation due to low desorption efficiency in the range 9.54–53.4%. However, the result of ionic strength revealed that the reaction was by outer sphere complexation. This study showed that morphologies play a vital role in the adsorption capacities of samples of hematite in the removal of Cr (VI) from aqueous solution.

Quasi-stable temperature of the steady state of microwave heated hematite

Microwave heated materials often reach a quasi-stable temperature resulting in thermal runaway. To control steady state in microwave processing, it is important to predict the quasi-stable temperature of the steady state. We demonstrated that the microwave heating behavior of hematite varies significantly with its initial temperature. In microwave heating, hematite samples could not be heated from room temperature, whereas hematite samples preheated to 410°C or higher was heated to a temperature of 1020°C. The microwave heating behavior can be accurately predicted by considering the steady-state energy balance.

Synthesis and Characterization of Hematite Nanoparticles as Active Photocatalyst for Water Splitting Application

This paper highlights on the hydrogen production through photocatalytic activity by using hematite nanoparticles synthesized from self-combustion method based on different stirring period. The morphologies and microstructures of the nanostructures were determined using Field-Emission Scanning Electron Microscope (FESEM), X-Ray Diffractometer (XRD) and Particle Size Analyser (PSA). Besides that, surface area analyser was used to determine the BET surface area of the hematite samples. The hematite nanocatalyst as-synthesized are proven to be rhombohedral crystalline hematite (α-Fe2O3) with particle diameters ranging from 60-140 nm. The BET specific surface area of hematite samples increased from 5.437 to 7.6425 m2/g with increasing stirring period from 1 to 4 weeks. This caused the amount of hydrogen gas produced from photocatalytic water splitting to increase as well.