Chemical elements
  Iron
    History of Iron
    Mineralogy
    Isotopes
    Energy
    Production
    Application
    Physical Properties
    Chemical Properties
      Iron Hydride
      Ferrous fluoride
      Aluminium pentafluoferrite
      Ferric fluoride
      Ammonium ferrifluoride
      Barium ferrifluoride
      Potassium ferrifluoride
      Sodium ferrifluoride
      Thallous ferrifluoride
      Ferrous diferrifluoride
      Ferrous monoferrifluoride
      Ferrous chloride
      Ammonium tetrachlorferrite
      Ferric chloride
      Tetrachlorferrates
      Pentachlorferrates
      Ferroso-ferric chloride
      Ferrous perchlorate
      Ferric perchlorate
      Ferrous chlorate
      Ferric chlorate
      Ferrous Oxychlorides
      Ferrous bromide
      Ferric bromide
      Ferric chloro-bromide
      Ferrous bromate
      Ferrous iodide
      Ferric iodide
      Ferric iodate
      Ferrous oxide
      Ferrous hydroxide
      Triferric tetroxide
      Ferric oxide
      Ferrous acid
      Calcium ferrite
      Cobalt ferrite
      Cupric ferrite
      Cuprous ferrite
      Magnesium ferrite
      Nickel ferrite
      Potassium ferrite
      Sodium ferrite
      Zinc ferrite
      Barium ferrate
      Strontium ferrate
      Barium perferrate
      Calcium perferrate
      Potassium perferrate
      Sodium perferrate
      Strontium perferrate
      Iron Subsulphides
      Ferrous sulphide
      Ferric sulphide
      Potassium ferric sulphide
      Sodium ferric sulphide
      Cuprous ferric sulphide
      Iron disulphide
      Ferrous sulphite
      Ferric sulphite
      Potassium ferri-tetrasulphite
      Potassium ferri-disulphite
      Potassium ferri-sulphite
      Ammonium ferri-sulphite
      Sodium ferri-disulphite
      Sodium hydrogen ferri-tetrasulphite
      Ferrous sulphate
      Ferrous copper sulphate Fe
      Ferrous ammonium sulphate
      Ferrous potassium sulphate
      Ferrous aluminium sulphate
      Basic ferrous sulphate
      Ferric sulphate
      Ammonium ferri-disulphate
      Trisodium ferri-trisulphate
      Ferric Alums
      Ferric ammonium alum
      Ferric potassium alum
      Ferric rubidium alum
      Ferroso-ferric sulphate
      Ferrous amido-sulphonate
      Ferric amido-sulphonate
      Ferrous thiosulphate
      Ferrous pyrosulphate
      Ferrous tetrathionate
      Ferric selenide
      Iron diselenide
      Iron Selenites
      Ferrous selenate
      Ferric rubidium selenium alum
      Ferric caesium selenium alum
      Ferric tellurite
      Ferrous chromite
      Ferrous chromate
      Iron nitride
      Nitro-Iron
      Ferrous nitrate
      Ferric nitrate
      Ferrous Nitroso Salts
      Potassium ferro-heptanitroso sulphide
      Sodium ferro-heptanitroso sulphide
      Ammonium ferro-heptanitroso sulphide
      Tetramethyl ammonium ferro-heptanitroso sulphide
      Ferro-dinitroso Sulphides
      Potassium ferro-dinitroso thiosulphate
      Triferro phosphide
      Diferro phosphide
      Iron monophosphide
      Iron sesqui-phosphide
      Ferrous hypophosphite
      Ferric hypophosphite
      Ferrous phosphite
      Ferric phosphite
      Ferrous orthophosphate
      Ferrous hydrogen orthophosphate
      Ferrous dihydrogen orthophosphate
      Ferric orthophosphate
      Sodium ferri-diorthophosphate
      Ammonium ferri-diorthophosphate
      Sodium ferri-triorthophosphate
      Ferric dihydrogen orthophosphate
      Acid ferric orthophosphate
      Ferrous metaphosphate
      Ferric metaphosphate
      Ferrous pyrophosphate
      Ferric pyrophosphate
      Hydrogen ferri-pyrophosphate
      Sodium ferro-pyrophosphate
      Ferrous thio-orthophosphite
      Ferrous thio-orthophosphate
      Ferrous thio-pyrophosphite
      Ferrous thio-pyrophosphate
      Iron sub-arsenide
      Iron mon-arsenide
      Iron sesqui-arsenide
      Iron di-arsenide
      Iron thio-arsenide
      Ferrous met-arsenite
      Ferric arsenite
      Ferrous ortho-arsenate
      Ferric ortho-arsenate
      Ferro mono-antimonide
      The di-antimonide
      Ferrous thio-antimonite
      Ferric ortho-antimonate
      Triferro carbide
      Diferro carbide
      Iron dicarbide
      Iron pentacarbonyl
      Diferro nonacarbonyl
      Iron tetracarbonyl
      Ferrous carbonate
      Ferrous bicarbonate
      Ferrous potassium carbonate
      Complex Iron Carbonates
      Ferrous thiocarbonate
      Ferrous thiocarbonate hexammoniate
      Ferrous cyanide
      Ferro-cyanic acid
      Aluminium ferrocyanide
      Aluminium ammonium ferrocyanide
      Ammonium ferrocyanide
      Barium ferrocyanide
      Calcium ferrocyanide
      Calcium ammonium ferrocyanide
      Cobalt ferrocyanide
      Copper ferrocyanide
      Ammonium cuproferrocyanide
      Barium cuproferrocyanide
      Lithium cuproferrocyanide
      Magnesium cuproferrocyanide
      Potassium cuproferrocyanide
      Sodium cuproferrocyanide
      Ammonium cupriferrocyanide
      Potassium cupriferrocyanide
      Potassium ferrous cupriferrocyanide
      Sodium cupriferrocyanide
      Strontium cupriferrocyanide
      Lithium ferrocyanide
      Magnesium ferrocyanide
      Magnesium ammonium ferrocyanide
      Manganese ferrocyanide
      Nickel ferrocyanide
      Potassium ferrocyanide
      Potassium aluminium ferrocyanide
      Potassium barium ferrocyanide
      Potassium calcium ferrocyanide
      Potassium cerium ferrocyanide
      Potassium magnesium ferrocyanide
      Potassium mercuric ferrocyanide
      Silver ferrocyanide
      Sodium ferrocyanide
      Sodium cerium ferrocyanide
      Strontium ferrocyanide
      Thallium ferrocyanide
      Zinc potassium ferrocyanide
      Ferricyanic acid
      Ammonium ferricyanide
      Barium ferricyanide
      Barium potassium ferricyanide
      Calcium ferricyanide
      Calcium potassium ferricyanide
      Cobalt ferricyanide
      Copper ferricyanide
      Lead ferricyanide
      Magnesium ferricyanide
      Mercuric ferricyanide
      Mercurous ferricyanide
      Potassium ferricyanide
      Sodium ferricyanide
      Strontium ferricyanide
      Zinc ferricyanide
      Ferrous hydrogen ferrocyanide
      Ferrous potassium ferrocyanide
      Prussian Blues
      Ferrous ferrocyanide
      Ferric ammonium ferrocyanide
      Nitroprussic acid
      Sodium nitroprusside
      Ammonium nitroprusside
      Barium nitroprusside
      Cobalt nitroprusside
      Nickel nitroprusside
      Potassium nitroprusside
      Carbonyl Penta-Ferrocyanides
      Carbonyl ferrocyanic acid
      Barium carbonyl ferrocyanide
      Copper carbonyl ferrocyanide
      Ferric carbonyl ferrocyanide
      Potassium carbonyl ferrocyanide
      Silver carbonyl ferrocyanide
      Sodium carbonyl ferrocyanide
      Strontium carbonyl ferrocyanide
      Uranyl carbonyl ferrocyanide
      Sodium ammonio ferrocyanide
      Potassium aquo ferrocyanide
      Potassium aquo ferricyanide
      Sodium aquo penta-ferricyanide
      Potassium sulphito ferrocyanide
      Ferrous thiocyanate
      Ferric thiocyanate
      Sodium ferrothiocyanate
      Sodium ferrithiocyanate
      Potassium ferrithiocyanate
      Iron subsilicide
      Iron monosilicide
      Iron disilicide
      Triferro disilicide
      Ferrous orthosilicate
      Ferrous magnesium orthosilicate
      Ferrous metasilicate
      Ferric silicate
      Diferro boride
      Iron monoboride
      Iron diboride
      Ferrous chlorborate
      Ferrous bromborate
    Corrosion
    Iron Salts
    PDB 101m-1aeb
    PDB 1aed-1awd
    PDB 1awp-1beq
    PDB 1bes-1c53
    PDB 1c6o-1ci6
    PDB 1cie-1cry
    PDB 1csu-1dfx
    PDB 1dgb-1dry
    PDB 1ds1-1e08
    PDB 1e0z-1ehj
    PDB 1ehk-1f5o
    PDB 1f5p-1fnp
    PDB 1fnq-1fzi
    PDB 1g08-1gnl
    PDB 1gnt-1h43
    PDB 1h44-1hdb
    PDB 1hds-1i5u
    PDB 1i6d-1iwh
    PDB 1iwi-1jgx
    PDB 1jgy-1k2o
    PDB 1k2r-1kw6
    PDB 1kw8-1lj0
    PDB 1lj1-1m2m
    PDB 1m34-1mko
    PDB 1mkq-1mun
    PDB 1muy-1n9x
    PDB 1naz-1nx4
    PDB 1nx7-1ofe
    PDB 1off-1p3t
    PDB 1p3u-1pmb
    PDB 1po3-1qmq
    PDB 1qn0-1ra0
    PDB 1ra5-1rxg
    PDB 1ry5-1smi
    PDB 1smj-1t71
    PDB 1t85-1u8v
    PDB 1u9m-1uyu
    PDB 1uzr-1vxf
    PDB 1vxg-1wri
    PDB 1wtf-1xlq
    PDB 1xm8-1y4r
    PDB 1y4t-1ygd
    PDB 1yge-1z01
    PDB 1z02-2a9e
    PDB 2aa1-2azq
    PDB 2b0z-2boz
    PDB 2bpb-2ca3
    PDB 2ca4-2cz7
    PDB 2czs-2dyr
    PDB 2dys-2ewk
    PDB 2ewu-2fwl
    PDB 2fwt-2gl3
    PDB 2gln-2hhb
    PDB 2hhd-2ibn
    PDB 2ibz-2jb8
    PDB 2jbl-2mgh
    PDB 2mgi-2o01
    PDB 2o08-2ozy
    PDB 2p0b-2q0i
    PDB 2q0j-2r1h
    PDB 2r1k-2spm
    PDB 2spn-2vbd
    PDB 2vbp-2vzb
    PDB 2vzm-2wiv
    PDB 2wiy-2xj5
    PDB 2xj6-2ylj
    PDB 2yrs-2zon
    PDB 2zoo-3a17
    PDB 3a18-3aes
    PDB 3aet-3bnd
    PDB 3bne-3cir
    PDB 3ciu-3dax
    PDB 3dbg-3e1p
    PDB 3e1q-3eh4
    PDB 3eh5-3fll
    PDB 3fm1-3gas
    PDB 3gb4-3h57
    PDB 3h58-3hrw
    PDB 3hsn-3ir6
    PDB 3ir7-3k9y
    PDB 3k9z-3l4p
    PDB 3l61-3lxi
    PDB 3lyq-3mm8
    PDB 3mm9-3n62
    PDB 3n63-3nlo
    PDB 3nlp-3o0f
    PDB 3o0r-3p6o
    PDB 3p6p-3prq
    PDB 3prr-3sel
    PDB 3sik-3una
    PDB 3unc-4blc
    PDB 4cat-4erg
    PDB 4erm-4nse
    PDB 4pah-8cat
    PDB 8cpp-9nse

Triferric tetroxide, Fe3O4






Ferroso-ferric oxide, Triferric tetroxide, Magnetite, or Magnetic oxide of iron, Fe3O4, occurs in nature as the mineral magnetite and may be regarded as a compound of ferrous oxide and ferric oxide, namely FeO.Fe2O3, or as the ferrous salt of hypothetical meta-ferrous acid, namely FeFe2O4. It has a black, metallic appearance, and crystallises in octahedra and dodecahedra, of hardness 5.5 to 6.5, and density approximately 4.9 to 5.2. It was first recognised as a definite oxide of iron by Gay-Lussac, who obtained it by the action of steam on iron. As its name would appear to imply, magnetite possesses magnetic properties, being attracted by a magnet. It is quite possible, however, that the name of the ore does not really refer to the magnet, but to Magnesia, a town in Lydia, Asia Minor, where the ore was first found. In the laboratory the oxide may be obtained in a variety of ways. Thus, when iron is heated in steam to upwards of 820° C., it becomes covered with a skin of magnetic oxide, the layers underneath consisting of various amounts of ferrous oxide associated with magnetic oxide in solid solution. If the iron is in the form of very thin plates, these may, by prolonged heating in the steam, be converted completely into the higher oxide.

Magnetic oxide also occurs as a superficial layer when iron is heated to dull redness in air - that is, at a temperature of 625° to 650° C. The oxide beneath the outermost skin has the composition represented by the formula Fe3O4.xFeO.

When ferric oxide is maintained at 1500° C. in nitrogen or at very high temperatures in air, such as those obtaining in the electric furnace, it is reduced to magnetite, for which reason it is possible, though scarcely profitable, to apply magnetic concentration to haematites at high temperatures. When iron burns in oxygen, the magnetic oxide is produced, and also when ferric oxide is heated to 400° C. in a current of hydrogen saturated with water vapour at 30° to 50° C. At higher temperatures products increasingly rich in ferrous oxide are obtained. Thus: -

700° С85 per cent. FeO
800° С92 per cent. FeO


On heating reduced iron in carbon dioxide at 440° C., and by reducing ferric oxide by hydrogen or carbon monoxide at 500° C., Moissan has been able to obtain the magnetic oxide.

Crystals of magnetic oxide have been obtained in a variety of ways, such as by calcination of sodium carbonate and ferrous chloride; by fusion of potassium sulphate and iron phosphate; by the action of hydrogen chloride upon heated ferrous oxide; and by ignition of ferrous fluoride with boric anhydride.

When strongly heated with excess of sodium chloride for several hours ferric oxide is converted into black crystals of magnetic oxide. Pure iron wire, heated to 1200° C. in a current of carbon dioxide, yields crystalline magnetic oxide, the crystals frequently exhibiting magnetic polarity. The presence of moisture facilitates the formation of larger crystals.

When iron wire is subjected to prolonged fusion with sodium sulphate, it is converted into magnetite, the sodium sulphate acting catalytically being first reduced to sulphite and re-oxidised to sulphate by the oxygen of the atmosphere. Ferrous sulphide may be oxidised to magnetite in a similar manner. As obtained in this manner, the crystalline magnetic oxide closely resembles the natural product. Its crystals are opaque, magnetic octahedra, possessed of a metallic lustre. Hardness 6 to 6.5; density, 5.21 to 5.25. The crystals are not affected by steam or carbon dioxide at bright red heat, are not attacked by diluted mineral acids, and are but slowly dissolved by the concentrated acids or aqua regia.

Ordinary magnetic oxide of iron melts at 1527° C. Its specific heat is 0.1655. When heated with platinum to 1600° C. in contact with air, magnetic oxide is reduced to the metal, oxygen being evolved, the iron passing into solid solution in the platinum. Under low oxygen pressures reduction in the above manner can take place at 1400° C. When heated in air for a prolonged period at 1300° C., the oxide is almost completely converted into ferric oxide. According to the reversible reaction 4Fe3O4 + O2 ⇔ 6Fe2O3,

magnetic oxide has no perceptible dissociation pressure at 1350° C.

It does not react appreciably with sulphur dioxide at dull redness. Raised to white heat in a current of hydrogen sulphide, it yields ferrous sulphide, accompanied by the evolution of hydrogen, sulphur dioxide, and a little sulphur trioxide.

When placed in freshly-fused potassium hydrogen sulphate, a crystal of magnetite is only slightly attacked; but at a higher temperature there is an energetic action.

Hydrogen reduces magnetic oxide to the metal, the reaction being perceptible at 305° C.

Magnetic oxide dissolves in hydrochloric acid. If the latter is not present in sufficient quantity to yield a complete solution of ferrous and ferric chlorides, ferric oxide and ferrous chloride are produced.

The heats of formation of magnetite are as follow: -

3[Fe2O3](calcined) = 2[Fe3O4] + (O) - 45,180 calories.
3[Fe] + 4(O) = [Fe3O4] + 265,200 calories.
3[Fe] + 4(O) = [Fe3O4] + 265,700 calories.
[FeO] + [Fe2O3] = [Fe3O4] + 9200 calories.
3[FeO] + (O) = [Fe3O4] + 85,800 calories.
3[FeO] + (O) = [Fe3O4] + 75,600 calories.
3[FeCO3] + (О) = [Fe3O4] + 3CO2 + 0 calories.
and at 490° C. under constant pressure,
3[Fe] + 4(O) = [Fe3O4] + 267,380 calories.

According to Moissan, magnetic oxide of iron exists in two polymorphic forms, according to its method of preparation. The one form, obtained by high temperature methods, such as the combustion of iron in oxygen, the action of steam on iron at red heat, and the calcination of ferric oxide at bright red heat, is characterised by its insolubility in concentrated boiling nitric acid, by its high density (5 to 5.09), and by its resistance to further oxidation when heated in air.

The second variety resembles the former in its black appearance and magnetic properties, but differs from it in density (4.86), in its solubility in nitric acid, and in its tendency to oxidise to ferric oxide when calcined in air. It is converted into the other variety when raised to white heat in nitrogen. As explained in the case of ferrous oxide, however, these differences may simply be due to variations in the states of aggregation of the oxide, according to its method of preparation.

Several substances, such as 4FeO.Fe2O3, 3FeO.Fe2O3, etc., have been described. It is highly probable, however, that these are not definite chemical entities.

When ferroso-ferric ammonium carbonate is decomposed by a hot concentrated solution of potassium hydroxide in the absence of air, hydrated ferroso-ferric oxide separates out, which, when dried at 100° C., corresponds in composition to the formula Fe2O3.4FeO.5H2O. It is readily acted on with air, yielding hydrated ferric oxide, Fe2O3.H2O.

A bluish black oxide, corresponding in composition to 2FeO.3Fe2O3, is described as resulting when potassium nitrate is added to a boiling solution of ferrous sulphate rendered alkaline with ammonia.


Hydrated Magnetic Oxide

Magnetic oxide dissolves in hydrochloric acid, and the solution so obtained yields, on pouring into an excess of sodium hydroxide solution, a black precipitate which, on drying, is attracted by a magnet. It is the monohydrate, Fe3O4.H2O.

The sesqui-hydrate, 2Fe3O4.3H2O, is obtained by precipitation in an analogous manner from mixed solutions of ferrous and ferric salts in the proportions theoretically required. The precipitate is dark green to black in colour, and strongly magnetic. It may be washed in the presence of air without oxidising, and loses water only, on heating.
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