Iron Oxide

Iron oxide is a compound that usually comes out of rocks in mountainous regions. This compound can not be touched with bare hands because the oxidizing gas in the compound comes into contact with air and becomes a flammable substance. This compound east of Eastern Anatolia in Turkey are in abundance in the province of Van.

 
 Iron oxides are chemical compounds composed of iron and oxygen. There are sixteen known iron oxides and oxyhydroxides, the best known of which is rust, a form of iron(III) oxide. Iron oxides and oxyhydroxides are widespread in nature and play an important role in many geological and biological processes.

Iron oxide materials yield pigments that are nontoxic, nonbleeding, weather resistant, and lightfast.   Natural iron oxides include a combination of one or more ferrous or ferric oxides, and impurities, such as manganese, clay, or organics.   Synthetic iron oxides can be produced in various ways, including thermal decomposition of iron salts, such as ferrous sulfate, to produce reds; precipitation to produce yellows, reds, browns, and blacks (e.g., the Penniman-Zoph process); and reduction of organic compounds by iron (e.g., nitrobenzene reduced to aniline in the presence of particular chemicals) to produce yellows and blacks.   Reds can be produced by calcining either yellow or blacks.

 

The most important reaction is its carbothermal reduction, which gives iron used in steel-making:

Fe2O3 + 3 CO → 2 Fe + 3 CO2

Another redox reaction is the extremely exothermic thermite reaction with aluminium.[13]

2 Al + Fe2O3 → 2 Fe + Al2O3

This process is used to weld thick metals such as rails of train tracks by using a ceramic container to funnel the molten iron in between two sections of rail. Thermite is also used in weapons and making small-scale cast-iron sculptures and tools.

Partial reduction with hydrogen at about 400 °C produces magnetite, a black magnetic material that contains both Fe(III) and Fe(II):[14]

3 Fe2O3 + H2 → 2 Fe3O4 + H2O

Iron(III) oxide is insoluble in water but dissolves readily in strong acid, e.g. hydrochloric and sulfuric acids. It also dissolves well in solutions of chelating agents such as EDTA and oxalic acid.

Heating iron(III) oxides with other metal oxides or carbonates yields materials known as ferrates (ferrate (III)):[14]

ZnO + Fe2O3 → Zn(FeO2)2

Practical Issue of Nanosized Colorant Particles

Kazuyuki Hayashi, in Nanoparticle Technology Handbook (Third Edition), 2018

2.1 Improved Dispersibility of Nanosized Iron Oxide Red Particles

Iron oxide has been used in many kinds of industrial applications because it is a rich element on the Earth and a multifunctional material. α-Fe2O3 (hematite) is the most popular material and it is often called “Bengara” or iron oxide red. Bengara has a long history from ancient wall painting [2]. α-Fe2O3 particles are manufactured by various procedures today. An example of manufacturing process is shown in Fig. 38.1. One of the most popular methods is wet synthesis, where iron sulfate and sodium hydrate are added to neutral reaction and oxidized to get iron oxide precursors such as Fe3O4 and α-FeOOH. Then the precursors are heated to derive α-Fe2O3 particles. Final particle size and distribution are almost decided by precursor's characteristics. Nanosized α-Fe2O3 particles have lower hiding power and can be applied for colorant particles as trans-iron oxide red, which have higher light transparency in coated films. Especially, a suitable trans-iron oxide red particle could be derived from nanosized acicular α-FeOOH precursors.

Figure 38.1. Schematic illustration of iron oxide–manufacturing process.

Particularly, UV light is absorbed by iron oxide red–coated film. The relationship between wavelength and light transparency in trans-iron oxide red–coated film is shown in Fig. 38.2. The light transparency of UV light is lower; however, IR light easily passes through the coated film. The relationship between particle size of iron oxide red particles and light transparency at λ = 700 nm is shown in Fig. 38.3. When the particle size is finer than 100 nm, light transparency becomes larger. Then, iron oxide pigment can be applied as transpigment for transparency film with a function of UV absorbent.

Figure 38.2. Light transparency of trans-iron oxide films.

Figure 38.3. The relationship between particle size and light transparency (λ = 700 nm).

The preparation procedure of trans-iron oxide red particles is mentioned as follows: iron sulfate solution and sodium carbonatesolution are mixed and aged in the reactor with N2-gas bubbling; then, the oxidation reaction occurs with aeration and nanosized α-FeOOH particles are synthesized in the reactor. α-FeOOH particles are washed and dried to derive α-FeOOH powder with acicular shape and particle size of 80 nm as precursor particles of iron oxide red pigment. α-FeOOH particles are heated at 250–400°C in the oven and dehydrated to α-Fe2O3 particles, and then nanosized iron oxide red particles are derived as shown in Fig. 38.4. Nanosized iron oxide red particles are hard to disperse because particle size is so small. It seems that they tend to coagulate together as shown in TEM photograph. It is necessary to introduce a surface treatment onto particles for easy dispersion. We recommend silicone coating onto iron oxide red particles to reduce their coagulation force between particles. Silicone additive is coated on nanosized iron oxide red particles in amounts such as 1, 1/2, 1/4, 1/8, 1/16, and 1/32-layer equivalent. If coagulation force between particles was reduced, particles would be dispersed well in the lacquer, and light transparency becomes higher in coloring film. Silicone-coated iron oxide red particles with 1/4-layer equivalent coating are shown in Fig. 38.5. It is found that particles are dispersed well and pulverized to almost primary particles. The results concerning lacquer dispersibility and transparent film are described in Table 38.1. The small amount of silicone surface treatment is effective for the dispersibility improvement of nanosized iron oxide red particles. Then, the lacquer viscosity is reduced and light transparency becomes higher. It is found that 1/8-layer equivalent silicone coating is enough for the practical use of nanosized iron oxide red particles. The appropriate surface treatment such as silicone coating is very effective for the practical use of nanosized iron oxide red particles.

Figure 38.4. trans-Iron oxide red particles.

Figure 38.5. Silicone-coated trans-iron oxide red particles.

Table 38.1. The Characteristics of Silicone-Coated trans-Iron Oxide Red Particles

 trans-Iron Oxide Red NontreatmentRun 1
1/32 Layer
Run 2
1/16 Layer
Run 3
1/8 Layer
Run 4
1/4 Layer
Run 5
1/2 Layer
Run 6
1 Layer
Particle size (nm)70696970696868
Specific surface area (m2/g)195.8183.8174.4165.9161.9149.1123.4
Si content (wt%)0.030.240.450.871.713.406.77
Lacquer viscosity (D = 1.92 s−1, cP)5120410033302970256022501990
Light transparency (λ = 700 nm, %)67.568.269.771.872.372.072.1

 

Pigment/binder ratio = 1/2.7, Film thickness = 17 μm.

 

High-performance electrospun nanostructured composite fiber anodes for lithium–ion batteries

Yuming Chen, ... Haitao Huang, in Multifunctionality of Polymer Composites, 2015

21.4.1.3.3 Iron oxides

Iron oxides, such as hematite (Fe2O3) and magnetite (Fe3O4), can store six or eight Li per formula unit (i.e., Fe2O3+6Li ↔ 3Li2O+2Fe and Fe3O4+8Li ↔ 4Li2O+3Fe) through the conversion reaction and are promising anodes that can deliver high theoretical specific capacities of 1007 and 926 mAh/g, respectively [72]. Iron oxides are abundant, low cost, and environment friendly [80]. However, practical application of iron oxide-based anodes is limited by the poor cycling life and large polarization due to the poor lithiation/delithiation kinetics. Several groups have shown that electrospun Fe2O3nanofibers [81] or nanorods [82] by electrospinning of PVP/ferric acetyl acetonate composite precursors and subsequent calcination as anodes showed high reversible capacities of 1095 mAh/g at 0.05C for nanorods and 1293 mAh/g at 0.06C for nanofibers with excellent cycle stability and rate capability. The high performance was ascribed to the interconnected porous structure with high surface area. Incorporating nanoscale iron oxides in carbon matrix can further increase the electrochemical property of the electrodes. The carbonaceous matrix improves the electrical conductivity of the electrodes and accommodates the huge stress during cycling. Iron oxide nanoparticles offer high capacity and assist electronic/ionic diffusion. Indeed, these iron oxide/carbon composites also enhance the initial reversible capacity and Coulombic efficiency. Hence, these nanostructured iron oxides–carbon composites showed high reversible capacity, long cycle life, and good rate capability when used as anodes for LIBs. Thus, Fe2O3 nanoparticles encapsulated in CNFs electrospun from FeCl3 and PAN in DMF showed an initial discharge capacity of approximately 604 mAh/g at a current density of 50 mA/g with a Coulombic efficiency of approximately 60% [83]. After 75 cycles, the reversible capacity still remained at approximately 488 mAh/g, corresponding to a capacity retention of 81%, suggesting a slow capacity loss.

Electron Magnetic Resonance - Applications in Physical Sciences and Biology

Daniel Farinha Valezi, ... Eduardo Di Mauro, in Experimental Methods in the Physical Sciences, 2019

Abstract

Iron oxides shows magnetic properties and are very common compounds present in soils and rocks. Electron magnetic resonance(EMR) is a reliable technique to study these properties when associated with other techniques such as magnetometry, Mossbauer spectroscopy and others. Thus, in this chapter we show how to obtain information from EMR spectroscopy from mineral samples both theoretically and experimentally. The minerals from Araucária site (Paraná state, Brazil) were separated by particle size fractionation and investigated by EMR at room temperature and 77K. The paramagnetic species in the soil samples were identified by comparison with EMR spectra of some minerals studied by our group, and several soil types and/or soil components investigated in the literature. Besides the study of paramagnetic species in soils, the iron oxide goethite was studied in more details. Goethite, despite its antiferromagnetic behavior, shows a magnetic component. The origin of the mechanism that create this magnetic component has been discussed in literature for about half of century. EMR was applied to different samples of goethite, natural and synthetic. It was studied the magnetic transition to the paramagnetic state that the mineral undergoes with increasing temperature. Besides, with different synthesis, it was related the magnetic properties, as analyzed by EMR results, with structural characteristics.

Biological Nanoscience

Y. Chen, ... W. Tan, in Comprehensive Nanoscience and Technology, 2011

2.04.5.1 Preparation of MNPs

Iron oxide core MNPs [90,91] were synthesized by coprecipitating iron salts. A mechanical stirrer was used to mix ammonium hydroxide (2.5%) with an iron chloride solution at 350 rpm for 10 min. The iron chloride solution contained ferric chloride hexahydrate (0.5 M), ferrous chloride tetrahydrate (0.25 M), and HCl (0.33 M). The iron oxide NPs were washed 3 times with 5 ml aliquots of H2O and once with a 5 ml aliquot of ethanol. Each wash was performed from decanting the supernatant, adding fresh wash solution, and redispersing in the fresh solution typically within 3–5 min. Then, the iron oxide NPs were dispersed in an ethanol solution containing ∼1.2% ammonium hydroxide at a final concentration of ∼7.5 mg ml−1.

The magnetite core particles were coated with silica by adding tetraethoxyorthosilicate (200 μl), and the mixture was sonicated for 90 min to complete the hydrolysis process. An additional aliquot of TEOS (10 μl) was added and again sonicated for 90 min to add a postcoating to the NPs. The sample was washed 3 times with ethanol to remove the excess reactants.

A solution of 0.1 mg ml−1 Fe3O4–SiO2 (silica-coated MNPs) in 10 mM phosphate buffered saline (PBS), pH 7.4, and a 5 mg ml−1 avidin solution in 10 mM PBS, pH 7.4, was vortexed for 5–10 min to initiate an avidin coating. The resulting sample was incubated at 4 °C for 12–14 h. Next, the particles were washed 3 times and dispersed at 1.2 mg ml−1 with 100 mM PBS. The avidin coating was stabilized by cross-linking the coated NPs with 1% glutaraldehyde (1 h at 25 °C). Again, the particles were magnetically separated, washed 3 times, and dispersed in 1 M Tris–HCl buffer. Incubation of the samples in the 1 M Tris–HCl buffer (3 h at 4 °C) was the next step, followed by three additional washes with 20 mM Tris–HCl, 5 mM MgCl2, pH 8.0, at a concen

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