Showing papers on "Magnetite published in 2002"

Size-Controlled Synthesis of Magnetite Nanoparticles

Abstract: Monodisperse magnetite nanoparticles have been synthesized by high-temperature solution-phase reaction of Fe(acac)3 in phenyl ether with alcohol, oleic acid, and oleylamine. Seed-mediated growth is used to control Fe3O4 nanoparticle size, and variously sized nanoparticles from 3 to 20 nm have been produced. The as-synthesized Fe3O4 nanoparticles have inverse spinel structure, and their assemblies can be transformed into γ-Fe2O3 or α-Fe nanoparticle assemblies, depending on the annealing conditions. The reported procedure can be used as a general approach to various ferrite nanoparticles and nanoparticle superlattices.

Formation of ferrihydrite and associated iron corrosion products in permeable reactive barriers of zero-valent iron.

Abstract: Ferrihydrite, which is known to form in the presence of oxygen and to be stabilized by the adsorption of Si, PO4 and SO4, is ubiquitous in the fine-grained fractions of permeable reactive barrier (PRB) samples from the U.S. Coast Guard Support Center (Elizabeth City, NC) and the Denver Federal Center (Lakewood, CO) studied by high-resolution transmission electron microscopy and selected area electron diffraction. The concurrent energy-dispersive X-ray data indicate a strong association between ferrihydrite and metals such as Si, Ca, and Cr. Magnetite, green rust 1, aragonite, calcite, mackinawite, greigite and lepidocrocite were also present, indicative of a geochemical environment that is temporally and spatially heterogeneous. Whereas magnetite, which is known to form due to anaerobic Fe0 corrosion, passivates the Fe0 surface, ferrihydrite precipitation occurs away from the immediate Fe0 surface, forming small (<0.1 microm) discrete clusters. Consequently, Fe0-PRBs may remain effective for a longer period of time in slightly oxidized groundwater systems where ferrihydrite formation occurs compared to oxygen-depleted systems where magnetite passivation occurs. The ubiquitous presence of ferrihydrite suggests that the use of Fe0-PRBs may be extended to applications that require contaminant adsorption rather than, or in addition to, redox-promoted contaminant degradation.

Magnetic Colloids from Magnetotactic Bacteria: Chain Formation and Colloidal Stability

Abstract: Single-domain magnetite (Fe3O4) crystals, harvested from magnetotactic bacteria, display on transmission electron micrographs the cluster morphologies (folded chains, flux-closure rings) predicted for magnetic colloids with dominant dipolar attractions. These strong attractions are responsible for the linear magnetite chains inside bacteria but do not affect the colloidal stability of the bacteria, as confirmed by analytic sedimentation experiments. Calculations of the interaction energy between dipole chains show that the magnetic component of the interbacteria interaction is negligible due to screening of dipolar forces: the bacteria sense only the geomagnetic field but not each other's compass.

Lamellar magnetism in the haematite-ilmenite series as an explanation for strong remanent magnetization.

Abstract: Magnetic anomalies associated with slowly cooled igneous and metamorphic rocks are commonly attributed to the presence of the mineral magnetite. Although the intermediate members of the ilmenite–haematite mineral series can also carry a strong ferrimagnetic remanence1, it is preserved only in rapidly cooled volcanic rocks, where formation of intergrowths of weakly magnetic haematite and paramagnetic ilmenite is suppressed. But the occurrence of unusually large and stable magnetic remanence in rocks containing such intergrowths has been known for decades2,3,4,5, and has recently been the subject of intense investigation6,7,8,9,10. These unmixed oxide phases have been shown to contain pervasive exsolution lamellae with thickness from 100 µm down to about 1 nm (one unit cell). These rocks, many of which contain only a few per cent of such oxides, show natural remanent magnetizations up to 30 A m-1—too strong to be explained even by pure haematite in an unsaturated state11,12. Here we propose a new ferrimagnetic substructure created by ferrous–ferric ‘contact layers’ that reduce charge imbalance along lamellar contacts between antiferromagnetic haematite and paramagnetic ilmenite. We estimate that such a lamellar magnetic material can have a saturation magnetization up to 55 kA m-1—22 times stronger than pure haematite—while retaining the high coercivity and thermal properties of single-domain haematite.

Reductive Dissolution and Biomineralization of Iron Hydroxide Under Dynamic Flow Conditions

Abstract: Iron cycling and the associated changes in solid phase have dramatic implications for trace element mobility and bioavailability. Here we explore the formation of secondary iron phases during microbially mediated reductive dissolution of ferrihydrite-coated sand under dynamic flow conditions. An initial period (10 d) of rapid reduction, indicated by consumption of lactate and production of acetate and Fe(II) to the pore water in association with a darkening of the column material, is followed by much lower rate of reduction to the termination of the experiment after 48 d. Although some Fe (<25%) is lost to the effluent pore water, the majority remains within the column as ferrihydrite (20−70%) and the secondary mineral phases magnetite (0−70%) and goethite (0−25%). Ferrihydrite converts to goethite in the influent end of the column where dissolved Fe(II) concentrations are low and converts to magnetite toward the effluent end where Fe(II) concentrations are elevated. A decline in the rate of Fe(II) produc...

Occurrence and prevention of photodissolution at the phase junction of magnetite and titanium dioxide

Abstract: A stable magnetic photocatalyst was prepared by coating a magnetic core with a layer of photoactive titanium dioxide. A direct deposition of titanium dioxide onto the surface of magnetic iron oxide particles proved ineffective in producing a stable magnetic photocatalyst, with high levels of photodissolution being observed with these samples. This observed photodissolution is believed to be due to the dissolution of the iron oxide phase, induced by the photoactive the titanium dioxide layer due to electronic interactions at the phase junction in these magnetic photocatalysts. The introduction of an intermediate passive SiO2 layer between the titanium dioxide phase and the iron oxide phase inhibited the direct electrical contact and hence prevented the photodissolution of the iron oxide phase. The magnetic photocatalyst is for use in slurry-type reactors from which the catalyst can be easily recovered by the application of an external magnetic field.

Direct imaging of nanoscale magnetic interactions in minerals

Abstract: The magnetic microstructure of a natural, finely exsolved intergrowth of submicron magnetite blocks in an ulvospinel matrix is characterized by using off-axis electron holography in the transmission electron microscope. Single-domain and vortex states in individual blocks, as well as magnetostatic interaction fields between them, are imaged at a spatial resolution approaching the nanometer scale. The images reveal an extremely complicated magnetic structure dominated by the shapes of the blocks and magnetostatic interactions. Magnetic superstates, in which clusters of magnetite blocks act collectively to form vortex and multidomain states that have zero net magnetization, are observed directly.

New field evidence bearing on the origin of the el laco magnetite deposit, northern chile—a discussion

Abstract: Sir: The El Laco ores occur as massive, horizontal, tabular bodies, as crosscutting dikes and/or vein networks, and as stratified, fragmental material. A controversy exists as to their origin. One group of investigators believes the orebodies formed from iron oxide magma that intruded the local volcanic sequence and in places erupted at the surface (see Naslund et al., 2002). Another group believes the deposits formed from hot, iron-rich fluids that completely replaced older silicate rocks (see Rhodes and Oreskes, 1999, and Rhodes, et al., 1999). Sillitoe and Burrows (2002) describe a number of outcrop features at El Laco which they suggest support a replacement origin. All of the features they describe, however, are consistent with the magmatic hypothesis, and many are inconsistent with a replacement origin. Blocks and fragments of andesite within magnetite ore at Laco Sur range in size from centimeters to >5 m and comprise roughly 5 vol percent of the orebody (Sillitoe and Burrows, 2002). In places, subhorizontal trains of blocks occur, and veins of magnetite cut some blocks. These observations, however, do not uniquely support a replacement origin for the ore. We interpret the magnetite orebody at Laco Sur to be a near-vent facies volcanic deposit with a mixture of viscous Fe oxide lavas, interbedded Fe oxide pyroclastic material, and xenoliths, as would be expected in this facies. Andesite blocks in friable magnetite tend to lie along particular horizons within the deposit as would be expected for air-fall deposits. All of the blocks have razor-sharp contacts with the enclosing magnetite. Many are altered to pyroxene and other silicates, but the only magnetite in these blocks is in the form of minor amounts of small, crosscutting veins. Where blocks are enclosed within massive ore, which we interpret to be iron oxide lavas, the magnetite is very …

Intracellular Iron Minerals in a Dissimilatory Iron-Reducing Bacterium

Abstract: Among prokaryotes, there are few examples of controlled mineral formation; the formation of crystalline iron oxides and sulfides [magnetite (Fe3O4) or greigite (Fe3S4)] by magnetotactic bacteria is an exception. Shewanella putrefaciens CN32, a Gram-negative, facultative anaerobic bacterium that is capable of dissimilatory iron reduction, produced microscopic intracellular grains of iron oxide minerals during growth on two-line ferrihydrite in a hydrogen-argon atmosphere. The minerals, formed at iron concentrations found in the soil and sedimentary environments where these bacteria are active, could represent an unexplored pathway for the cycling of iron by bacteria.

Understanding soluble arsenate removal kinetics by zerovalent iron media.

Abstract: Zerovalent iron filings have been proposed as a filter medium for removing arsenic compounds from potable water supplies. This research investigated the kinetics of arsenate removal from aqueous solutions by zerovalent iron media. Batch experiments were performed to determine the effect of the iron corrosion rate on the rate of As(V) removal. Tafel analyses were used to determine the effect of the As(V) concentration on the rate of iron corrosion in anaerobic solutions. As(V) removal in column reactors packed with iron filings was measured over a 1-year period of continuous operation. Comparison of As(V) removal by freely corroding and cathodically protected iron showed that rates of arsenate removal were dependent on the continuous generation of iron oxide adsorption sites. In addition to adsorption site availability, rates of arsenate removal were also limited by mass transfer associated with As(V) diffusion through iron corrosion products. Steady-state removal rates in the column reactor were up to 10 times faster between the inlet-end and the first sampling port than between the first sampling port and the effluent-end of the column. Faster removal near the influent-end of the column was due to a faster rate of iron oxidation in that region. The presence of 100 microg/L As(V) decreased the iron corrosion rate by up to a factor of 5 compared to a blank electrolyte solution. However, increasing the As(V) concentration from 100 to 20,000 microg/L resulted in no further decrease in the iron corrosion rate. The kinetics of arsenate removal ranged between zeroth- and first-order with respect to the aqueous As(V) concentration. The apparent reaction order was dependent on the availability of adsorption sites and on the aqueous As(V) concentration. X-ray absorption spectroscopy analyses showed the presence of iron metal, magnetite (Fe3O4), an Fe(III) oxide phase, and possibly an Fe(II,III) hydroxide phase in the reacted iron filings. These mixed valent oxide phases are not passivating and permit sustained iron corrosion and continuous generation of new sites for As(V) adsorption.

Structural and magnetic properties of core?shell iron?iron oxide nanoparticles

Abstract: We present studies of the structural and magnetic properties of core–shell iron–iron oxide nanoparticles. α-Fe nanoparticles were fabricated by sputtering and subsequently covered with a protective nanocrystalline oxide shell consisting of either maghaemite (γ-Fe2O3) or partially oxidized magnetite (Fe3O4). We observed that the nanoparticles were stable against further oxidation, and Mossbauer spectroscopy at high applied magnetic fields and low temperatures revealed a stable form of partly oxidized magnetite. The nanocrystalline structure of the oxide shell results in strong canting of the spin structure in the oxide shell, which thereby modifies the magnetic properties of the core–shell nanoparticles.

Thermal and electrical properties of magnetite filled polymers

Abstract: By the addition of metal-oxide particles to plastics the electrical and thermal conductivity of polymers can be increased significantly. Such particle filled polymers can substitute metals and metal oxides in applications like radio frequency interference shielding. Furthermore, particle filled polymers with higher thermal conductivity than unfilled ones become more and more important in applications with decreasing geometric dimensions and increasing output of power, like in computer chips. Therefore, thermal and electrical properties of polypropylene and polyamide with metal-oxide particle filler (magnetite, Fe 3 O 4 ) are investigated. Different particle sizes of magnetite and types of additives were added in various proportions to a standard polypropylene and polyamide in an extrusion process. Samples were prepared by injection molding to investigate thermal and electrical properties systematically. The thermal conductivity increases from 0.22 to 0.93 W/(m K) for a filler content of 44 vol% of magnetite, whereas the electrical resistivity decreases more than seven orders of magnitude from an insulator (0% of magnetite) to 10 kΩ m (47 vol% of magnetite). The experimental results of thermal and electrical conductivity were correlated to the amount and particle sizes of magnetite filler. Electrical resistivity shows a significant drop at the theoretical percolation threshold (∼0.33) and for filler contents exceeding 33 vol% the magnetite particles have point contacts and are surrounded by the polymer matrix.

Theoretical models of intermediate and inverse AMS fabrics

Abstract: [1] Multi-domain magnetites display a normal anisotropy of magnetic susceptibility (AMS) fabric where grain shape axes coincide with AMS axes. By contrast, single-domain magnetite has an inverse magnetic fabric where magnetic axes are interchanged. The mixing of normal and inverse magnetic fabrics results in intermediate fabrics. Theoretical models for intermediate fabrics consider all combinations of normal and inverse fabrics. The minimum amount of inverse component required for intermediate fabrics to form is about 20% in the case of prolate normal (T = -0.50) and prolate inverse (T = -0.42) components. Such a small amount of inverse component may not be noticed. The anisotropy resulting from intermediate fabrics is lower than that of the normal or inverse contribution to AMS. This suggests that whenever intermediate fabrics occur neither the shape factor nor the degree of anisotropy relate to strain in a simple way.

Origin of supposedly biogenic magnetite in the Martian meteorite Allan Hills 84001

Abstract: Crystals of magnetite (Fe3O4) and periclase (MgO) in Fe-Mg-Ca carbonate in the Martian meteorite Allan Hills 84001 were studied by using transmission electron microscopy to understand their origin and evaluate claims that the magnetites were made by Martian microorganisms. In magnesian carbonate, periclase occurs as aggregates of crystals (grain size ≈3 nm) that are preferentially oriented with respect to the carbonate lattice. Larger periclase crystals ≈50 nm in size are commonly associated with voids of similar size. Periclase clearly formed by precipitation from carbonate as a result of partial decomposition and loss of CO2. Magnetite occurs in more ferroan carbonate, and, like periclase, it is associated with voids and microfractures and the two oxides may be intermixed. Magnetite nanocrystals that are commonly euhedral and entirely embedded in carbonate are topotactically oriented with respect to the carbonate lattice, showing that they formed as solid-state precipitates. Magnetites in Fe-rich carbonate rims are not well oriented. These magnetites are generally more irregular in shape and diverse in size than the euhedral variety. All occurrences of magnetite and periclase are entirely consistent with in situ growth by solid-state diffusion as a result of carbonate decomposition during impact heating. Biogenic sources should not be invoked for any magnetites.

Aeromagnetic And Aeroradiometric Response To Hydrothermal Alteration

Abstract: In Precambrian terrains all regional and most local intensive magnetic anomalies are produced by magnetite. Monoclinic pyrrhotite is responsible for some local, but often intensive, magnetic anomaly patterns. Both magnetite and pyrrhotite are affected by hydrothermal alteration processes in various ways, resulting in changes either in abundance or in grain fabric. These changes are recorded in the magnetic properties of the altered rock units and reflected in their aeromagnetic signatures. Hydrothermal alteration in deformed bedrock zones is commonly controlled by structural or tectonic features. Regional high-resolution aerogeophysical surveys can be utilized, in both re- gional and detailed investigations, to map the overall geological and tectonic setting or to estimate local changes in magnetic mineralogy and the relative abundance of radionuclides. Magnetite is most commonly destroyed in alteration processes, such as biotitization, carbonation, sulfidization and silicification. The progressive destruction of magnetite begins at grain margins and results first in broken and cracked grain texture and smaller grain size, then progresses to total disap- pearance of magnetite. Alteration in magnetite- bearing rock units may be recognized by decreased magnetic intensity and by the broken, disrupted magnetic pattern. The abundance of monoclinic pyrrhotite is enhanced by reducing hydrothermal fluids, and typical crystal anisotropy is developed due to tectonic stress. The relative contents of radioelements are changed in the same hydrothermal processes and partly for the same reasons as the ferrimagnetic minerals. Potassic alteration often results in elevated K radiation particularly for mafic rocks, and then anomalous K/Th ratios along local shear or fracture zones may be indicative of gold-bearing mineralization. On the other hand, high U/Th ratios within metasedimentary units may point out prospects for sulphidization. Although variation of U/Th ra- tios largely reflects the environmental conditions during primary diagenesis or a later deformational phase, mainly the decrease in Th radiation close to sulphide mineralization seems to be responsible for the elevated U/Th ratios.

Study of the oxide/carbide transition on iron surfaces during catalytic coke formation

Abstract: The thermodynamic equilibria between metallic iron, iron oxides, iron carbides and a hydrocarbon/hydrogen mixture were calculated at 600°C. On the basis of metastable Fe-C-O phase diagram, iron oxides can be converted directly into carbides in a reducing and carburizing atmosphere. Experimental results on the rate of oxide/carbide conversion are reported. Thermogravimetric measurements have been performed in an iC 4 H 10 -H 2 -Ar atmosphere at 600°C on preoxidized iron samples. The kinetics of the oxide layer transformation were studied by sequential exposure experiments. Scanning electron microscopy observations and x-ray diffraction analysis have been carried out. The results lead to the conclusion that magnetite (Fe 3 O 4 ) is transformed into carbide particles, acting as a catalyst for graphitic filament growth. The initial stages of the oxide/carbide transition were studied by x-ray photoelectron spectroscopy. The results confirm that no metallic iron was formed during the transformation.

Synthesis of magnetite nanoparticles and the process of forming Fe-based nanomaterials

Abstract: A method and structure for making magnetite nanoparticle materials by mixing iron salt with alcohol, carboxylic acid and amine in an organic solvent and heating the mixture to 200–360 C is described. The size of the particles can be controlled either by changing the iron salt to acid/amine ratio or by coating small nanoparticles with more iron oxide. Magnetite nanoparticles in the size ranging from 2 nm to 20 nm with a narrow size distribution are obtained with the invention. The invention can be readily extended to other iron oxide based nanoparticle materials, including M Fe 2 O 4 (M=Co, Ni, Cu, Zn, Cr, Ti, Ba, Mg) nanomaterials, and iron oxide coated nanoparticle materials. The invention also leads to the synthesis of iron sulfide based nanoparticle materials by replacing alcohol with thiol in the reaction mixture. The magnetite nanoparticles can be oxidized to γ-Fe 2 O 3 , or α-Fe 2 O 3 , or can be reduced to bcc-Fe nanoparticles, while iron oxide based materials can be used to make binary iron based metallic nanoparticles, such as CoFe, NiFe, and FeCoSmx nanoparticles.

Phase-Selective Deposition and Microstructure Control in Iron Oxide Films Obtained by Single-Source CVD

Abstract: Iron(III) tert-butoxide, [Fe(O t Bu) 3 ] 2 , was used as a single source for iron and oxygen to obtain nanocrystalline hematite (Fe 2 O 3 ) or magnetite (Fe 3 O 4 ) films by low-pressure (LP) CVD. The decomposition profile of the molecular precursor and the crystallization temperature of iron oxide were derived from thermogravimetry/differential thermal analysis (TG/DTA). The substrate temperature was found to markedly influence the morphology and Fe/O stoichiometry in the deposited films. The morphological features and phase identification of the grown films were obtained by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The compositional identity of the phases was determined by the X-ray photoelectron spectroscopy (XPS) of the CVD deposits. Annealing the films ex-situ under reducing or oxidizing conditions allows selective interconversion (Fe 2 O 3 ↔ Fe 3 O 4 ) among the deposited phases with no particle size variation. The interplay between the rate of precursor delivery and substrate temperature controlled the mean particle size in the films. Magnetite film with a mean particle size of 10 nm was obtained on silicon at 450 °C. Formation of larger grains and grain clusters was observed at higher temperatures. High coercivity (4000 Oe) and small saturation magnetization (0.3 emu g -1 ) of the Fe 3 O 4 film confirmed superparamagnetic behavior due to small particle size. Absorption spectra of magnetite and hematite films deposited on glass show them to be transparent to the visible light. The sheet resistance of nanocrystalline Fe 3 O 4 and Fe 2 O 3 films was found to be 2.4 kΩ and 2 MΩ, respectively.

Sorption and reduction of neptunium(V) on the surface of iron oxides

Abstract: Sorption and desorption experiments of Np on magnetite and hematite under aerobic and anaerobic conditions were carried out to investigate the possibility of reduction of Np(V) to Np(IV) at pH 4 to 8 within 7 days. The amount of sorbed Np on magnetite under anaerobic conditions was about 2 or 3 times greater than that under aerobic conditions. Furthermore, the results of desorption experiments indicated that the dominant sorption behavior of Np on magnetite under anaerobic conditions was quite different from that under aerobic conditions. The oxidation state of Np sorbed on the iron oxides was determined by extraction technique using 0.5 M TTA in xylene and 2.0 M HNO 3 solution from the solid phase after sorption experiment. 90% and 10% of extracted Np was Np(IV) for magnetite system under anaerobic and aerobic conditions, respectively. On the other hand, almost 100% of extracted Np was Np(V) for hematite system under both aerobic and anaerobic conditions. These results indicated that Np(V) was reduced to Np(lV) by Fe(II) in magnetite. Redox reaction between Np(V) and Fe(II) was also studied in homogeneous solution without solid to decide if Fe(II) ions released from magnetite into silution or Fe(II) on the solid cause the reduction. Only 6% of Np(V) was reduced by Fe(II) at pH = 4 and 6 even after 7 days. According to this result, it was conjectured that the reduction of Np(V) to Np(IV) takes place not in the liquid phase by Fe(II) ion but on the surface of magnetite.

Role of the Alloy and Spinel in the Catalytic Behavior of Fe−Co/Cobalt Magnetite Composites under CO and CO2 Hydrogenation

Abstract: The aim of this work is to compare the reactivity and the transformation of the Fe−Co alloy on the one side and the Co-containing magnetite on the other side in Fe−Co/Co-containing magnetite catalysts after CO/H2 and CO2/H2 reactions. Different Co-to-Fe ratios are studied. The catalysts undergo different modifications owing to their initial composition, but especially to the gas mixtures. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) show that iron and cobalt carbides are formed in both cases: the iron carbides are formed first and are located on the particle surface while the cobalt carbides are formed in a second step and localized in the center. The spinel lattice parameter keeps constant values in CO/H2, while it decreases in CO2/H2. Furthermore the CO/H2 reaction occurs without a preliminary reduction unlike under CO2/H2 for which it is necessary. We propose that the carbides came preferentially from the Fe−Co alloy under CO/H2 and from the spinel under CO2/H2....

Structural and magnetic transformation of monodispersed iron oxide particles in a reducing atmosphere

Abstract: Uniform metal iron ellipsoidal particles of around 200 nm in length were obtained by reduction and passivation of alumina-coated α–Fe2O3 (hematite) particles under different conditions of temperature and hydrogen flow rate. The monodispersed hematite particles were prepared by the controlled hydrolysis of ferric sulfate and further coated with a homogeneous thin layer of Al2O3 by careful selection of the experimental conditions, mainly pH and aluminum salt concentration. The reduction mechanism of α–Fe2O3 into α–Fe was followed by x-ray and electron diffraction, and also by the measurements of the irreversible magnetic susceptibility. The transformation was found to be topotactic with the [001] direction of hematite particles, which lies along the long axis of the particles, becoming the [111] direction of magnetite and finally the [111] direction of metal iron. Temperature and hydrogen flow rate during the reduction have been found to be important parameters, which determine not only the degree of reduct...

Oxidation of Low-Carbon, Low-Silicon Mild Steel at 450–900°C Under Conditions Relevant to Hot-Strip Processing

Abstract: The oxidation behavior of a low-carbon, low-silicon mild steel was investigated in ambient air at 450–900°C to simulate steel strip oxidation during finishing hot rolling and coiling. Oxide scales developed at 880–900°C for a very short time (12 sec) had a structure similar to that formed on pure iron, but with a greater thickness ratio between the magnetite and wustite layers. However, the scale structure after oxidation for a longer period (200 sec) at 900°C deviated significantly from that reported for pure iron. This difference was attributed to the loss of scale–steel adhesion at some locations. Oxide scales formed in the range of 580–700°C after oxidation for more than 2 hr also differed from those reported for pure iron. The scale structures were irregular, comprising mainly hematite and magnetite with no or very little wustite, while the thickness ratio of these two layers differed considerably at different locations. The scale formed at 450–560°C was relatively uniform with a two-layered (hematite and magnetite) structure; however, the thickness ratio of these two scale layers varied for different oxidation temperatures and different oxidation durations. It was also found that limited oxygen supply (zero air flow) improved the scale–steel adhesion, and substantially reduced the relative thickness of the hematite layer. Continuous-cooling experiments proved that significant growth of the hematite layer, as well as the entire scale layer, may occur if the steel is cooled slowly through the temperature range 600–660°C, and even more significantly through the range 660–720°C.