What is Fe in chemistry

VIII. Subgroup / 8. Group / Fe / Co / Ni group

Iron is only rarely found in solid form (except in the earth's core) (Fe meteorites). Practically the most important iron ores are oxides such as magnetic iron stone Fe3O4 (Magnetite), Roteisenstein Fe2O3 (Hematite, glass head) or brown iron stone (main component: goethite, FeOOH). In addition, the simple carbonate, Spateisenstein or Siderite FeCO are known from bivalent iron3, the water-containing phosphate vivianite (blue iron earth, Fe3[PO4]2. 8 H.2O) and numerous silicates (e.g. fayalite, Fe2[SiO4]). The most important sulphides are iron gravel (FeS) and pyrite (FeS2), both also contain Fe (II) (see photos in Fig. 9.8.1). XX Vivianite + new magnetites XX

in the laboratory can iron be obtained by reduction with hydrogen:

Fe2O3 + H2 ⟶ 400-700OC ⟶ Fe + H2O

The technical manufacture has been earlier (up to approx. 1600) carried out in so-called racing ovens:

Coal + ore ⟶ slag (runs off) + rag (remains)

see G. Agricola, 1556, German translation, illustration p. 365

The production of steel takes place today in two steps:

  1. Production of pig iron
    Pig iron contains approx. 4% dissolved carbon, is brittle and cannot be forged. Red iron stone (Fe2O3, Iron content approx. 40-65%) or magnetic iron stone (magnetite, Fe3O4, 45-70% Fe) (see Fig. 9.8.1.) And also coal or coke and additives such as lime and various silicates are layered in a blast furnace. In addition, is so-called wind, preheated, with O2 enriched air from 1300OC and 4 bar required.
    Fig. 9.8.2. Sketch for the production of pig iron in the blast furnace‣SVG

    The blast furnace itself (see Fig. 9.8.2.) Is approx. 40 m high and approx. 15 m wide at the bottom. The slope is adapted to the change in volume of the filling. Coke and ore are alternately filled into the blast furnace, plus the lime aggregates, which lead to slagging (formation of easily melting Ca silicates / aluminates) of the Si and Al components. For operation: (steps from bottom to top):

    1. Igniting the lowest C-layer:
      2 C + O2 ⟶ 2 CO (-222 kJ)
      This reaction is exothermic, responsible for the high temperature in the entire blast furnace and drives the overall endothermic reduction of the iron oxides. In the following steps 2 and 3, this results in the overall strongly endothermic direct reduction of Fe2+ to Fe0 reached:
      2 FeO + C ⟶ 2 Fe + CO2 (+138.2 kJ)
      In the process (see step 2), CO ultimately acts as a reducing agent, which is reproduced again and again by setting the Boudouard equilibrium (see step 3).
    2. CO rises into the ore layer and acts as a reducing agent. This creates CO2.
      FeO + CO ⟶ Fe + CO2 (-17.5 kJ / mol)
      This reduction step is slightly exothermic.
    3. The Boudouard equilibrium is restored in the next layer of coke:
      CO2 + C ⟶ 2 CO (+172.6 kJ / mol)
      that, since it is an endothermic reaction, at high temperatures (approx.> 800 OC) is on the right.
    4. In the reduction zone occurs at around 600OC is the reduction of Fe3+ to Fe2+.
      Fe2O3 + CO ⟶ Fe3O4 + CO2 (-47.3 kJ)
      Fe3O4 + CO ⟶ 3 FeO + CO2 (+36.8 kJ)
      This reduction of Fe takes place right at the top of the blast furnace, i.e. at low temperatures3+ to Fe2+ with the last CO. The Boudouard equilibrium (see above) is already on the left, CO2 no longer reacts to CO with the coke.
    The products of the blast furnace process as a whole are:
    • Pig iron with a C content of approx. 2-4%
    • so-called gout with the composition: 50% N2, 30% CO and 15% CO2which is used to heat the wind because of its still considerable calorific value.
    • Slag, Ca silicates / aluminates, which can be used in road construction.
  2. Steelmaking
    Steel is the name given to iron that can be hardened by quenching. In addition, the reduction of the C component, the so-called Decarburization of pig iron (also Freshen up called) required. The phase diagram Fe-C (see Fig. 9.8.3.)
    Fig. 9.8.3. Phase diagram Fe-C (red: 2-phase areas, gray: single-phase areas)‣SVG

    shows the individual ranges for steels according to carbon content:

    • Pig iron: 2.5-4% C
    • Steel in the narrower sense: 0.4 - 1.7% C. Steel can be hardened by heating to 800 OC and subsequent quenching: At 800O As the phase diagram shows, C initially forms what is known as austenite, γ-iron with dissolved carbon. During quenching, metastable martensite (α-Fe, in which carbon is dissolved) is formed. The conversion of the f.c.c. packing (e.g. from γ-Fe) into the b.c.c. structure (e.g. from α-Fe) is therefore generally referred to as Martensitic phase transformation designated. 33% of all steels produced are stainless V2A steels, (Fig. 9.8.4. Left: designation V2A / X5CrNi18-10 or 1.4301).
    • Structural steel (including wrought iron) contains less than 0.4% carbon. (Fig. 9.8.4. Right: designations: RSt37-2 (old) or S235JR (new))
      V2A steel plate (V2A / X5CrNi18-10 or 1.4301)Plate made of structural steel (RSt37-2 or S235JR)
      Fig. 9.8.4. V2A steel and structural steel
    Technically, decarburization can be carried out using two methods:
    1. At the Fresh wind the raw iron is first completely decarburized through
      1. Injection of air (Thomas method).
      2. Inflate O2 (Linz-Donauwitzer- short LD process), which is the main process today.
      The decarburization takes place in tiltable devices (converters, see also with the copper extraction)
      • basic feed (CaO) (Thomas pear) (for ores containing P)
        P.2O5 ⟶ Approx3(PO4)2
        (The resulting calcium phosphate is used as fertilizer (Thomas flour).)
      • sour food (Bessemer pear) (lining: quartz / clay, rarely used today)
      carried out. The oxidation is carried out in approx. 15 minutes, then the converter is tilted on its broad side in order to pour off the slag. Mirror iron or ferromanganese is added for recarburization.
    2. At the Stove freshening the raw iron is immediately decarburized to the correct carbon content. It used to be Siemens-Martin ovens used. Today scrap (iron oxide) is fused with the pig iron in an electric arc furnace (electric steel mill, direct or alternating current). Iron oxide (rust / scrap) reacts with the residual carbon of the pig iron according to:
      Fe2O3 + 3 C ⟶ 2 Fe + 3 CO
The following (historical) Summary (Fig. 9.8.5.) Shows again the most important processes in steel production.
Fig. 9.8.5. Extraction of steel (historical and schematic; note: the processes listed on the left (e.g. 'ingots') are no longer in use today Puddle oven pig iron was decarburized in the semi-solid state.

Links and literature on iron and steel production

  • Classic instructional video (in German, nice footage)
  • and 'the mouse' of course
  • and a 10 min. video about the whole process (Acero AHMSA, Mexico)
  • G. Agricola, 1556, German translation (on iron and steel: from p. 364, e.g. picture p. 365)
  • www.stahlseite.de good photos all about iron and steel
  • Video about the electric steelworks, including continuous casting (Stainless Steel Production Process)
  • Völklinger Hütte
  • Picture gallery industrial monument Landscape Park Duisburg-Nord
  • Experiments on iron and steel (Uni Bielefeld)
  • Wikipedia on the blast furnace
  • The Steel brooch (Verlag Stahleisen GmbH, Düsseldorf, 2002).
  • and as with all technical processes the Ullmann
9.8.6. Pourbaix diagram of iron‣SVG
d6-Ion, salts very similar to the Mg salts, in many silicates e.g. associated with Mg. In the presence of oxygen and / or water, + III is the most common oxidation state of iron. This is found in salts and complexes d5-Ion generally in the high-spin configuration (maximum spin multiplicity). An important exception to this is the complex with the (very strong) cyanido ligands, e.g. in the 'red blood liquor salt', K3[Fe (CN)6]. The chemistry of Fe3+ is Al's3+ extremely comparable, practically all salts are isotypic. The separation of the two very common metals from each other is based on the amphoteric of aluminum, which is absent in Fe (III) (see Al extraction in Section 4.2.) Or the possibility of reduction to Fe (II) (separation as Fe silicates ('Slag') or as 'green salt' in technical separation processes).
Fe (III) oxides / hydroxides are by far the most frequently used yellow (goethite) and red pigments (α-Fe2O3), some examples are shown in Figure 9.8.7. to see. (For the structures of the pure substances, see the Al oxides / hydroxides in Chapter 4.4.)

The mixed-valent 'iron black' Fe3O4 is the second most important black pigment after pure carbon, which e.g. cannot be used in ceramics or concretes etc. Fe3O4 is also a magnetic pigment because of its ferrimagnetism.

The maximum oxidation state of iron is +6 (d2), which e.g. in the orthotetraoxidoferrate (VI) ion [FeO4]2- is present. This violet ion is only stable in the strongly basic (i.e. with the unprotonated 'hard' oxido ligands) (see experiment and Pourbaix in Fig. 9.8.XX). As with permanganate or chromates, the color is based on an LM-CT process.

Production of Fe (VI)
The production of the tetraoxido-ferrate (VI) ion [FeO4]2- succeeds with the help of elemental chlorine, which is released 'in-situ' from chloride and chlorite. The violet ion is only stable in the basic (see Pourbaix diagram); in the acidic it is immediately reduced to Fe (III) hydroxide.


Elemental cobalt (Fig. 9.8.XX) crystallizes in the hexagonal close packing of spheres.
Fig. 9.8.XXX: Elemental cobalt
Rinmann's green is zinc oxide (ZnO), which turns green when small amounts of Co (II) ions are incorporated. If too large quantities of cobalt are used during production, the co-spinel Co is created3O4containing Co (II) and Co (III) side by side.

Production of Rinnmanns Grün
Successful (and unsuccessful) production of Rinmanns Grün, a Co (II) - 'doped' ZnO. The black product that is obtained when working with too high a Co concentration is a spinel with Co (III) ions, either directly Co3O4 or also ZnCo2O4.

Also in Thenards blue CoAl2O4 (see Chapter 4.4. for Al and spinels) Co (II) is in tetrahedral coordination. The colors are created by d-d-Transitions in the tetrahedral ligand field (see also the experiment 'secret ink' in complex chemistry in chapter 8.3.). 'Smalte' (see Fig. 9.8.XX) is a glass that is colored with Co (II) ions; finely ground smalt was used as a blue pigment in the Middle Ages. The 'Co-Glass' known from the laboratory is also composed in the same way. The preliminary test on cobalt with the borax or phosphorus salt bead is based on the same principle.

SmaltCoAl2O4 (Thenard blue)
9.8.XX. Some Co (II) pigments
Of cobalt in the oxidation state + III (d6) there are a large number of classic 'Werner' complexes. Although cobalt is the 3rdd-Metals no strong splitting of the dStates, the octahedral LS configuration, and thus diamagnetic complexes, is almost always present, even with weak ligands.
Photos of some complexes from our collection follow HERE Very important Co-rich alloys that are used as permanent magnets are SmCo5 and Sm2Co7, which were discussed with the samarium, i.e. with the lanthanides in chapter 7.1.
Elemental nickel (Fig. 9.8.XX) crystallizes in the cubic closest packing of spheres.
Fig. 9.8.XXX: Elemental nickel
In the case of nickel, the bivalent dominates the chemistry in aqueous systems. The d8-Ion is mostly octahedral, more rarely and only coordinated in a square planar manner with ligands that specify this geometry (the classic: DADO). Tetrahedral complexes are also known, especially those with larger ligands. Ni (III) compounds such as NiO (OH) are also known. Finally, there are 'hard' ligands such as oxide or fluoride d6-Systems with mostly octahedral coordinated Ni (IV), such as NiO2 (see Li-ion battery) or K2[NiF6].
- no attempts without tuition fees -
- no attempts without tuition fees -
- no attempts without tuition fees - ... but at least from the F internship ...
9.8.XX Pt crucible