Как написать оксид железа 3

Оксид железа (III)

Оксид железа (III) – это твердое, нерастворимое в воде вещество красно-коричневого цвета.

Способы получения

Оксид железа (III) можно получить различными методами:

1. Окисление оксида железа (II) кислородом.

 4FeO   +   O₂   →   2Fe₂O₃

2. Разложение гидроксида железа (III) при нагревании:

2Fe(OH)₃   →   Fe₂O₃   +  3H₂O

Химические свойства

Оксид железа (III) – амфотерный.

1. При взаимодействии оксида железа (III) с кислотными оксидами и кислотами образуются соли.

Например, оксид железа (III) взаимодействует с азотной кислотой:

Fe₂O₃  +  6HNO₃   →  2Fe(NO₃)₃  +  3H₂O

2. Оксид железа (III) взаимодействует с щелочами и основными оксидами. Реакция протекает в расплаве, при этом образуется соответствующая соль (феррит).

Например, оксид железа (III) взаимодействует с гидроксидом натрия:

Fe₂O₃  +  2NaOH   →   2NaFeO₂  +  H₂O

3. Оксид железа (III) не взаимодействует с водой.

4. Оксид железа (III) окисляется сильными окислителями до соединений железа (VI).

Например, хлорат калия в щелочной среде окисляет оксид железа (III) до феррата: 

Fe₂O₃  +  KClO₃  +  4KOH   →  2K₂FeO₄  +  KCl  +  2H₂O

Нитраты и нитриты в щелочной среде также окисляют оксид железа (III):

Fe₂O₃  +  3KNO₃  +  4KOH   →  2K₂FeO₄  +  3KNO₂  +  2H₂O

5. Оксид железа (III) проявляет окислительные свойства. Но есть интересный нюанс — при восстановлении оксида железа (III), как правило, образуется смесь продуктов: это может быть оксид железа (II), просто вещество железо, или железная окалина Fe₃O₄. Но в реакции мы записываем при этом только один продукт. А вот какой именно это будет продукт, зависит от условий реакции. Как правило, в экзаменах по химии нам даются указания на возможный продукт (цвет образовавшегося вещества или дальнейшие характерные реакции).

Например, оксид железа (III) реагирует с угарным газом при нагревании. При этом возможно восстановление как до простого железа, так и до оксида железа (II) или железной окалины:

Fe₂O₃  +  3СO  →  2Fe  +  3CO₂

Fe₂O₃  +  СO  →  2FeO  +  CO₂

3Fe₂O₃  +  СO  →  2Fe₃O₄  +  CO₂

При восстановлении оксида железа (III) водородом также возможно образование различных продуктов, например, простого железа:

Fe₂O₃  +  3Н₂  →  2Fe  +  3H₂O

Железом можно восстановить оксид железа только до оксида железа (II):

Fe₂O₃  +  Fe   →  3FeO 

Оксид железа (III) реагирует с более активными металлами.

Например, с алюминием (алюмотермия):

Fe₂O₃  +  2Al  →  2Fe  +  Al₂O₃

Оксид железа (III) реагирует также с некоторыми другими сильными восстановителями.

Например, с гидридом натрия:

Fe₂O₃  +  3NaH  →  3NaOH  +  2Fe

6. Оксид железа (III) – твердый, нелетучий  и амфотерный. А следовательно, он вытесняет более летучие оксиды (как правило, углекислый газ) из солей при сплавлении.

Например, из карбоната натрия:

Fe₂O₃  +  Na₂CO₃ → 2NaFeO₂  +  CO₂

Металлы

Неметаллы

Щелочные

Щелоч-зем

Благородные

Галогены

Халькогены

Полуметаллы

s-элементы

p-элементы

d-элементы

f-элементы

Оксид железа (III) – неорганическое вещество, имеет химическую формулу Fe₂O₃.

Краткая характеристика оксида железа (III)

Модификации оксида железа (III)

Физические свойства оксида железа (III)

Получение оксида железа (III)

Химические свойства оксида железа (III)

Химические реакции оксида железа (III)

Применение и использование оксида железа (III)

Краткая характеристика оксида железа (III):

Оксид железа (III) – неорганическое вещество красно-коричневого цвета.

Оксид железа (III) содержит три атома кислорода и два атома железа.

Химическая формула оксида железа (III) Fe₂O₃.

В воде не растворяется. С водой не реагирует.

Термически устойчив.

Оксид железа (III) – амфотерный оксид с большим преобладанием основных свойств. Как амфотерный оксид проявляет в зависимости от условий либо основные, либо кислотные свойства.

Модификации оксида железа (III):

Известны следующие кристаллические модификации железа: α-Fe₂O₃, γ-Fe₂O₃.

Физические свойства оксида железа (III)*:

Наименование параметра:	Значение:
Химическая формула	Fe2O3
Синонимы и названия иностранном языке	iron(III) oxide (англ.) гематит (рус.) красный железняк (рус.)
Тип вещества	неорганическое
Внешний вид	красно-коричневые тригональные кристаллы
Цвет	красно-коричневый
Вкус	—**
Запах	—
Агрегатное состояние (при 20 °C и атмосферном давлении 1 атм.)	твердое вещество
Плотность (состояние вещества – твердое вещество, при 20 °C), кг/м3	5242
Плотность (состояние вещества – твердое вещество, при 20 °C), г/см3	5,242
Температура кипения, °C	1987
Температура плавления, °C	1566
Молярная масса, г/моль	159,69

Примечание:

* оксид железа α-форма.

** — нет данных.

Получение оксида железа (III):

В природе встречается в виде минералов гематита (красный железняк), лимонита и маггемита.

Оксид железа (III) получают в результате следующих химических реакций:

1. 1. окисления железа:

4Fe + 3O₂ → 2Fe₂O₃.

1. 2. термического разложения полигидрата оксида железа (III):

Fe₂O₃•nH₂O →  Fe₂O₃ + nH₂O (t = 500-700 ^oC).

1. 3. термического разложения метагидроксида железа:

2FeO(OH) → Fe₂O₃ + H₂O (t = 500-700 ^oC).

1. 4. термического разложения гидроксида железа (III):

2Fe(OH)₃ → Fe₂O₃ + 3H₂O (t°).

1. 5. термического разложения сульфата железа (III):

Fe₂(SO₄)₃ → Fe₂O₃ + 3SO₃ (t = 500-700 ^oC).

Химические свойства оксида железа (III). Химические реакции оксида железа (III):

Оксид железа (III) относится к амфотерным оксидам, но с большим преобладанием основных свойств.

Химические свойства оксида железа (III) аналогичны свойствам амфотерных оксидов других металлов. Поэтому для него характерны следующие химические реакции:

1. реакция оксида железа (III) с алюминием:

2Al + Fe₂O₃ → 2Fe +  Al₂О (t°).

В результате реакции образуется оксид алюминия и железо.

2. реакция оксида железа (III) с углеродом:

Fe₂O₃ + 3С → 2Fe + 3CО (t°).

В результате реакции образуется железо и оксид углерода.

3. реакция оксида железа (III) с водородом:

Fe₂O₃ + H₂ → 2FeO + H₂О (t°),

Fe₂O₃ + 3H₂ → 2Fe + 3H₂О (t = 1050-1100 °C),

3Fe₂O₃ + H₂ → 2Fe₃O₄ + H₂О (t = 400 °C).

В результате реакции в первом случае образуется оксид железа (II) и вода, во втором – железо и вода, в третьем – оксид железа (II, III) и вода.

4. реакция оксида железа (III) с железом:

Fe₂O₃ + Fe → 3FeО (t = 900 °C).

В результате реакции образуется оксид железа (II).

5. реакция оксида железа (III) с оксидом натрия:

5Na₂О + Fe₂O₃ → 2Na₅FeО₄ (t = 450-500 °C).

В результате реакции образуется соль – феррат натрия.

6. реакция оксида железа (III) с оксидом магния:

MgО + Fe₂O₃ → MgFe₂О₄ (t°).

В результате реакции образуется соль – феррит магния.

7. реакция оксида железа (III) с оксидом меди (II):

CuО + Fe₂O₃ → CuFe₂О₄ (t°).

В результате реакции образуется соль – феррит меди.

8. реакция оксида железа (III) с оксидом титана:

TiО + Fe₂O₃ → TiFe₂О₄ (t°).

В результате реакции образуется соль – феррит титана.

9. реакция оксида железа (III) с оксидом марганца:

MnО + Fe₂O₃ → MnFe₂О₄ (t°).

В результате реакции образуется соль – феррит марганца.

10. реакция оксида железа (III) с оксидом никеля:

NiО + Fe₂O₃ → NiFe₂О₄ (t°).

В результате реакции образуется соль – феррит никеля.

11. реакция оксида железа (III) с оксидом кадмия:

CdО + Fe₂O₃ → CdFe₂О₄ (t°).

В результате реакции образуется соль – феррит кадмия.

12. реакция оксида железа (III) с оксидом цинка:

ZnО + Fe₂O₃ → ZnFe₂О₄ (t = 450-500 °C),

ZnО + Fe₂O₃ → Fe₂ZnО₄ (t = 450-500 °C).

В результате реакции образуется оксид железа-цинка.

13. реакция оксида железа (III) с оксидом кальция:

CaО + Fe₂O₃ → CaFe₂О₄ (t = 900-1000 °C)

В результате реакции образуется оксид кальция-железа.

14. реакция оксида железа (III) с оксидом углерода:

Fe₂O₃ + 3СО → 2Fe + 3СО₂ (t = 700 °C),

Fe₂O₃ + СО → 2FeО + СО₂ (t = 500-600 °C),

3Fe₂O₃ + СО → 2Fe₃О4 + СО₂ (t = 400 °C),

В результате реакции в первом случае образуется железо и углекислый газ, во втором – оксид железа (II) и углекислый газ, в третьем – оксид железа (II, III) и углекислый газ.

15. реакция оксида железа (III) с гидроксидом натрия:

Fe₂O₃ + 2NaOH → 2NaFeO₂ + H₂О (t  = 600 ^oC, p).

В результате реакции образуется соль – феррит натрия и вода. Реакция протекает при избыточном давлении.

16. реакция оксида железа (III) с карбонатом натрия:

Fe₂O₃ + Na₂СO₃ → 2NaFeO₂ + СО₂ (t  = 800-900 ^oC).

В результате реакции образуется соль – феррит натрия и оксид углерода.

17. реакция оксида железа (III) с плавиковой кислотой:

Fe₂O₃ + 6HF → 2FeF₃ + 3H₂O.

В результате химической реакции получается соль – фторид железа и вода.

18. реакция оксида железа (III) с азотной кислотой:

Fe₂O₃ + 6HNO₃ → 2Fe(NO₃)₃ + 3H₂O.

В результате химической реакции получается соль – нитрат железа и вода. Азотная кислота – разбавленный раствор.

Аналогично проходят реакции оксида железа и с другими кислотами.  

19. реакция оксида железа (III) с бромистым водородом (бромоводородом):

Fe₂O₃ + 6HBr → 2FeBr₃ + 3H₂O.

В результате химической реакции получается соль – бромид железа и вода.

20. реакция оксида железа (III) с йодоводородом:

Fe₂O₃ + 6HI → 2FeI₃ + 3H₂O.

В результате химической реакции получается соль – йодид железа и вода.

21. реакция оксида железа (III) с хлоридом железа:

Fe₂O₃ + FeСl₃ → 3FeOCl₃ (t  = 350 ^oC).

В результате химической реакции получается оксид хлорида-железа.

22. реакция термического разложения оксида железа (III):

6Fe₂O₃ → 4Fe₃O₄ + O₂ (t  = 1200-1390 ^oC).

В результате химической реакции получается оксид железа (II, III) и кислород.

Применение и использование оксида железа:

Оксид железа используется в металлургии для выплавки чугуна, как катализатор в химической и нефтехимической промышленности, как пищевая добавка (E172), как компонент керамики, красок и пр. целей.

Примечание: © Фото //www.pexels.com, //pixabay.com

оксид железа реагирует кислота 1 2 3 4 5 вода
уравнение реакций соединения масса взаимодействие оксида железа
реакции с оксидом железа

Коэффициент востребованности
14 303

From Wikipedia, the free encyclopedia

This article is about a red-colored oxide of iron. For other uses, see Red Iron.

Iron(III) oxide

Fe   O
Names
IUPAC name Iron(III) oxide
Other names ferric oxide, haematite, ferric iron, red iron oxide, rouge, maghemite, colcothar, iron sesquioxide, rust, ochre
Identifiers
CAS Number	1309-37-1
3D model (JSmol)	Interactive image
ChEBI	CHEBI:50819
ChemSpider	14147
ECHA InfoCard	100.013.790
EC Number	215-168-2
E number	E172(ii) (colours)
Gmelin Reference	11092
KEGG	C19424
PubChem CID	518696
RTECS number	NO7400000
UNII	1K09F3G675
CompTox Dashboard (EPA)	DTXSID0029632
InChI InChI=1S/2Fe.3O [inchi] Key: JEIPFZHSYJVQDO-UHFFFAOYSA-N [inchi] InChI=1/2Fe.3O/rFe2O3/c3-1-4-2(3)5-1 Key: JEIPFZHSYJVQDO-ZVGCCQCPAC
SMILES O1[Fe]2O[Fe]1O2
Properties
Chemical formula	Fe2O3
Molar mass	159.687 g·mol−1
Appearance	Red-brown solid
Odor	Odorless
Density	5.25 g/cm3[1]
Melting point	1,539 °C (2,802 °F; 1,812 K)[1] decomposes 105 °C (221 °F; 378 K) β-dihydrate, decomposes 150 °C (302 °F; 423 K) β-monohydrate, decomposes 50 °C (122 °F; 323 K) α-dihydrate, decomposes 92 °C (198 °F; 365 K) α-monohydrate, decomposes[3]
Solubility in water	Insoluble
Solubility	Soluble in diluted acids,[1] barely soluble in sugar solution[2] Trihydrate slightly soluble in aq. tartaric acid, citric acid, CH3COOH[3]
Magnetic susceptibility (χ)	+3586.0×10−6 cm3/mol
Refractive index (nD)	n1 = 2.91, n2 = 3.19 (α, hematite)[4]
Structure
Crystal structure	Rhombohedral, hR30 (α-form)[5] Cubic bixbyite, cI80 (β-form) Cubic spinel (γ-form) Orthorhombic (ε-form)[6]
Space group	R3c, No. 161 (α-form)[5] Ia3, No. 206 (β-form) Pna21, No. 33 (ε-form)[6]
Point group	3m (α-form)[5] 2/m 3 (β-form) mm2 (ε-form)[6]
Coordination geometry	Octahedral (Fe3+, α-form, β-form)[5]
Thermochemistry[7]
Heat capacity (C)	103.9 J/mol·K[7]
Std molar entropy (S⦵298)	87.4 J/mol·K[7]
Std enthalpy of formation (ΔfH⦵298)	−824.2 kJ/mol[7]
Gibbs free energy (ΔfG⦵)	−742.2 kJ/mol[7]
Hazards
GHS labelling:
Pictograms	[8]
Signal word	Warning
Hazard statements	H315, H319, H335[8]
Precautionary statements	P261, P305+P351+P338[8]
NFPA 704 (fire diamond)	[10] 0 0 0
Threshold limit value (TLV)	5 mg/m3[1] (TWA)
Lethal dose or concentration (LD, LC):
LD50 (median dose)	10 g/kg (rats, oral)[10]
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 10 mg/m3[9]
REL (Recommended)	TWA 5 mg/m3[9]
IDLH (Immediate danger)	2500 mg/m3[9]
Related compounds
Other anions	Iron(III) fluoride
Other cations	Manganese(III) oxide Cobalt(III) oxide
Related iron oxides	Iron(II) oxide Iron(II,III) oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).  verify (what is  ?) Infobox references

Iron(III) oxide or ferric oxide is the inorganic compound with the formula Fe₂O₃. It is one of the three main oxides of iron, the other two being iron(II) oxide (FeO), which is rare; and iron(II,III) oxide (Fe₃O₄), which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe₂O₃ is the main source of iron for the steel industry. Fe₂O₃ is readily attacked by acids. Iron(III) oxide is often called rust, and to some extent this label is useful, because rust shares several properties and has a similar composition; however, in chemistry, rust is considered an ill-defined material, described as Hydrous ferric oxide.^[11]

Structure[edit]

Fe₂O₃ can be obtained in various polymorphs. In the main one, α, iron adopts octahedral coordination geometry. That is, each Fe center is bound to six oxygen ligands. In the γ polymorph, some of the Fe sit on tetrahedral sites, with four oxygen ligands.

Alpha phase[edit]

α-Fe₂O₃ has the rhombohedral, corundum (α-Al₂O₃) structure and is the most common form. It occurs naturally as the mineral hematite which is mined as the main ore of iron. It is antiferromagnetic below ~260 K (Morin transition temperature), and exhibits weak ferromagnetism between 260 K and the Néel temperature, 950 K.^[12] It is easy to prepare using both thermal decomposition and precipitation in the liquid phase. Its magnetic properties are dependent on many factors, e.g. pressure, particle size, and magnetic field intensity.

Gamma phase[edit]

γ-Fe₂O₃ has a cubic structure. It is metastable and converted from the alpha phase at high temperatures. It occurs naturally as the mineral maghemite. It is ferromagnetic and finds application in recording tapes,^[13] although ultrafine particles smaller than 10 nanometers are superparamagnetic. It can be prepared by thermal dehydratation of gamma iron(III) oxide-hydroxide. Another method involves the careful oxidation of iron(II,III) oxide (Fe₃O₄).^[13] The ultrafine particles can be prepared by thermal decomposition of iron(III) oxalate.

Other solid phases[edit]

Several other phases have been identified or claimed. The β-phase is cubic body-centered (space group Ia3), metastable, and at temperatures above 500 °C (930 °F) converts to alpha phase. It can be prepared by reduction of hematite by carbon,^{[clarification needed]} pyrolysis of iron(III) chloride solution, or thermal decomposition of iron(III) sulfate.^[14]

The epsilon (ε) phase is rhombic, and shows properties intermediate between alpha and gamma, and may have useful magnetic properties applicable for purposes such as high density recording media for big data storage.^[15] Preparation of the pure epsilon phase has proven very challenging. Material with a high proportion of epsilon phase can be prepared by thermal transformation of the gamma phase. The epsilon phase is also metastable, transforming to the alpha phase at between 500 and 750 °C (930 and 1,380 °F). It can also be prepared by oxidation of iron in an electric arc or by sol-gel precipitation from iron(III) nitrate.^{[citation needed]} Research has revealed epsilon iron(III) oxide in ancient Chinese Jian ceramic glazes, which may provide insight into ways to produce that form in the lab.^{[16][non-primary source needed]}

Additionally, at high pressure an amorphous form is claimed.^{[6][non-primary source needed]}

Liquid phase[edit]

Molten Fe₂O₃ is expected to have a coordination number of close to 5 oxygen atoms about each iron atom, based on measurements of slightly oxygen deficient supercooled liquid iron oxide droplets, where supercooling circumvents the need for the high oxygen pressures required above the melting point to maintain stoichiometry.^[17]

Hydrated iron(III) oxides[edit]

Several hydrates of Iron(III) oxide exist.
When alkali is added to solutions of soluble Fe(III) salts, a red-brown gelatinous precipitate forms. This is not Fe(OH)₃, but Fe₂O₃·H₂O (also written as Fe(O)OH).
Several forms of the hydrated oxide of Fe(III) exist as well. The red lepidocrocite (γ-Fe(O)OH) occurs on the outside of rusticles, and the orange goethite (α-Fe(O)OH) occurs internally in rusticles.
When Fe₂O₃·H₂O is heated, it loses its water of hydration. Further heating at 1670 K converts Fe₂O₃ to black Fe₃O₄ (Fe^IIFe^III₂O₄), which is known as the mineral magnetite.
Fe(O)OH is soluble in acids, giving [Fe(H₂O)₆]³⁺. In concentrated aqueous alkali, Fe₂O₃ gives [Fe(OH)₆]³⁻.^[13]

Reactions[edit]

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.^[18]

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):^[19]

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)):^[19]

ZnO + Fe₂O₃ → Zn(FeO₂)₂

Preparation[edit]

Iron(III) oxide is a product of the oxidation of iron. It can be prepared in the laboratory by electrolyzing a solution of sodium bicarbonate, an inert electrolyte, with an iron anode:

4 Fe + 3 O₂ + 2 H₂O → 4 FeO(OH)

The resulting hydrated iron(III) oxide, written here as FeO(OH), dehydrates around 200 °C.^[19][20]

2 FeO(OH) → Fe₂O₃ + H₂O

Uses[edit]

Iron industry[edit]

The overwhelming application of iron(III) oxide is as the feedstock of the steel and iron industries, e.g. the production of iron, steel, and many alloys.^[20]

Polishing[edit]

A very fine powder of ferric oxide is known as «jeweler’s rouge», «red rouge», or simply rouge. It is used to put the final polish on metallic jewelry and lenses, and historically as a cosmetic. Rouge cuts more slowly than some modern polishes, such as cerium(IV) oxide, but is still used in optics fabrication and by jewelers for the superior finish it can produce. When polishing gold, the rouge slightly stains the gold, which contributes to the appearance of the finished piece. Rouge is sold as a powder, paste, laced on polishing cloths, or solid bar (with a wax or grease binder). Other polishing compounds are also often called «rouge», even when they do not contain iron oxide. Jewelers remove the residual rouge on jewelry by use of ultrasonic cleaning. Products sold as «stropping compound» are often applied to a leather strop to assist in getting a razor edge on knives, straight razors, or any other edged tool.

Pigment[edit]

Iron(III) oxide is also used as a pigment, under names «Pigment Brown 6», «Pigment Brown 7», and «Pigment Red 101».^[21] Some of them, e.g. Pigment Red 101 and Pigment Brown 6, are approved by the US Food and Drug Administration (FDA) for use in cosmetics. Iron oxides are used as pigments in dental composites alongside titanium oxides.^[22]

Hematite is the characteristic component of the Swedish paint color Falu red.

Magnetic recording[edit]

Iron(III) oxide was the most common magnetic particle used in all types of magnetic storage and recording media, including magnetic disks (for data storage) and magnetic tape (used in audio and video recording as well as data storage). Its use in computer disks was superseded by cobalt alloy, enabling thinner magnetic films with higher storage density.^[23]

Photocatalysis[edit]

α-Fe₂O₃ has been studied as a photoanode for solar water oxidation.^[24] However, its efficacy is limited by a short diffusion length (2–4 nm) of photo-excited charge carriers^[25] and subsequent fast recombination, requiring a large overpotential to drive the reaction.^[26] Research has been focused on improving the water oxidation performance of Fe₂O₃ using nanostructuring,^[24] surface functionalization,^[27] or by employing alternate crystal phases such as β-Fe₂O₃.^[28]

Medicine[edit]

Calamine lotion, used to treat mild itchiness, is chiefly composed of a combination of zinc oxide, acting as astringent, and about 0.5% iron(III) oxide, the product’s active ingredient, acting as antipruritic. The red color of iron(III) oxide is also mainly responsible for the lotion’s pink color.

See also[edit]

• Chalcanthum

References[edit]

External links[edit]

• NIOSH Pocket Guide to Chemical Hazards

From Wikipedia, the free encyclopedia

This article is about a red-colored oxide of iron. For other uses, see Red Iron.

Iron(III) oxide

Fe   O
Names
IUPAC name Iron(III) oxide
Other names ferric oxide, haematite, ferric iron, red iron oxide, rouge, maghemite, colcothar, iron sesquioxide, rust, ochre
Identifiers
CAS Number	1309-37-1
3D model (JSmol)	Interactive image
ChEBI	CHEBI:50819
ChemSpider	14147
ECHA InfoCard	100.013.790
EC Number	215-168-2
E number	E172(ii) (colours)
Gmelin Reference	11092
KEGG	C19424
PubChem CID	518696
RTECS number	NO7400000
UNII	1K09F3G675
CompTox Dashboard (EPA)	DTXSID0029632
InChI InChI=1S/2Fe.3O [inchi] Key: JEIPFZHSYJVQDO-UHFFFAOYSA-N [inchi] InChI=1/2Fe.3O/rFe2O3/c3-1-4-2(3)5-1 Key: JEIPFZHSYJVQDO-ZVGCCQCPAC
SMILES O1[Fe]2O[Fe]1O2
Properties
Chemical formula	Fe2O3
Molar mass	159.687 g·mol−1
Appearance	Red-brown solid
Odor	Odorless
Density	5.25 g/cm3[1]
Melting point	1,539 °C (2,802 °F; 1,812 K)[1] decomposes 105 °C (221 °F; 378 K) β-dihydrate, decomposes 150 °C (302 °F; 423 K) β-monohydrate, decomposes 50 °C (122 °F; 323 K) α-dihydrate, decomposes 92 °C (198 °F; 365 K) α-monohydrate, decomposes[3]
Solubility in water	Insoluble
Solubility	Soluble in diluted acids,[1] barely soluble in sugar solution[2] Trihydrate slightly soluble in aq. tartaric acid, citric acid, CH3COOH[3]
Magnetic susceptibility (χ)	+3586.0×10−6 cm3/mol
Refractive index (nD)	n1 = 2.91, n2 = 3.19 (α, hematite)[4]
Structure
Crystal structure	Rhombohedral, hR30 (α-form)[5] Cubic bixbyite, cI80 (β-form) Cubic spinel (γ-form) Orthorhombic (ε-form)[6]
Space group	R3c, No. 161 (α-form)[5] Ia3, No. 206 (β-form) Pna21, No. 33 (ε-form)[6]
Point group	3m (α-form)[5] 2/m 3 (β-form) mm2 (ε-form)[6]
Coordination geometry	Octahedral (Fe3+, α-form, β-form)[5]
Thermochemistry[7]
Heat capacity (C)	103.9 J/mol·K[7]
Std molar entropy (S⦵298)	87.4 J/mol·K[7]
Std enthalpy of formation (ΔfH⦵298)	−824.2 kJ/mol[7]
Gibbs free energy (ΔfG⦵)	−742.2 kJ/mol[7]
Hazards
GHS labelling:
Pictograms	[8]
Signal word	Warning
Hazard statements	H315, H319, H335[8]
Precautionary statements	P261, P305+P351+P338[8]
NFPA 704 (fire diamond)	[10] 0 0 0
Threshold limit value (TLV)	5 mg/m3[1] (TWA)
Lethal dose or concentration (LD, LC):
LD50 (median dose)	10 g/kg (rats, oral)[10]
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 10 mg/m3[9]
REL (Recommended)	TWA 5 mg/m3[9]
IDLH (Immediate danger)	2500 mg/m3[9]
Related compounds
Other anions	Iron(III) fluoride
Other cations	Manganese(III) oxide Cobalt(III) oxide
Related iron oxides	Iron(II) oxide Iron(II,III) oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).  verify (what is  ?) Infobox references

Iron(III) oxide or ferric oxide is the inorganic compound with the formula Fe₂O₃. It is one of the three main oxides of iron, the other two being iron(II) oxide (FeO), which is rare; and iron(II,III) oxide (Fe₃O₄), which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe₂O₃ is the main source of iron for the steel industry. Fe₂O₃ is readily attacked by acids. Iron(III) oxide is often called rust, and to some extent this label is useful, because rust shares several properties and has a similar composition; however, in chemistry, rust is considered an ill-defined material, described as Hydrous ferric oxide.^[11]

Structure[edit]

Fe₂O₃ can be obtained in various polymorphs. In the main one, α, iron adopts octahedral coordination geometry. That is, each Fe center is bound to six oxygen ligands. In the γ polymorph, some of the Fe sit on tetrahedral sites, with four oxygen ligands.

Alpha phase[edit]

α-Fe₂O₃ has the rhombohedral, corundum (α-Al₂O₃) structure and is the most common form. It occurs naturally as the mineral hematite which is mined as the main ore of iron. It is antiferromagnetic below ~260 K (Morin transition temperature), and exhibits weak ferromagnetism between 260 K and the Néel temperature, 950 K.^[12] It is easy to prepare using both thermal decomposition and precipitation in the liquid phase. Its magnetic properties are dependent on many factors, e.g. pressure, particle size, and magnetic field intensity.

Gamma phase[edit]

γ-Fe₂O₃ has a cubic structure. It is metastable and converted from the alpha phase at high temperatures. It occurs naturally as the mineral maghemite. It is ferromagnetic and finds application in recording tapes,^[13] although ultrafine particles smaller than 10 nanometers are superparamagnetic. It can be prepared by thermal dehydratation of gamma iron(III) oxide-hydroxide. Another method involves the careful oxidation of iron(II,III) oxide (Fe₃O₄).^[13] The ultrafine particles can be prepared by thermal decomposition of iron(III) oxalate.

Other solid phases[edit]

Several other phases have been identified or claimed. The β-phase is cubic body-centered (space group Ia3), metastable, and at temperatures above 500 °C (930 °F) converts to alpha phase. It can be prepared by reduction of hematite by carbon,^{[clarification needed]} pyrolysis of iron(III) chloride solution, or thermal decomposition of iron(III) sulfate.^[14]

The epsilon (ε) phase is rhombic, and shows properties intermediate between alpha and gamma, and may have useful magnetic properties applicable for purposes such as high density recording media for big data storage.^[15] Preparation of the pure epsilon phase has proven very challenging. Material with a high proportion of epsilon phase can be prepared by thermal transformation of the gamma phase. The epsilon phase is also metastable, transforming to the alpha phase at between 500 and 750 °C (930 and 1,380 °F). It can also be prepared by oxidation of iron in an electric arc or by sol-gel precipitation from iron(III) nitrate.^{[citation needed]} Research has revealed epsilon iron(III) oxide in ancient Chinese Jian ceramic glazes, which may provide insight into ways to produce that form in the lab.^{[16][non-primary source needed]}

Additionally, at high pressure an amorphous form is claimed.^{[6][non-primary source needed]}

Liquid phase[edit]

Molten Fe₂O₃ is expected to have a coordination number of close to 5 oxygen atoms about each iron atom, based on measurements of slightly oxygen deficient supercooled liquid iron oxide droplets, where supercooling circumvents the need for the high oxygen pressures required above the melting point to maintain stoichiometry.^[17]

Hydrated iron(III) oxides[edit]

Several hydrates of Iron(III) oxide exist.
When alkali is added to solutions of soluble Fe(III) salts, a red-brown gelatinous precipitate forms. This is not Fe(OH)₃, but Fe₂O₃·H₂O (also written as Fe(O)OH).
Several forms of the hydrated oxide of Fe(III) exist as well. The red lepidocrocite (γ-Fe(O)OH) occurs on the outside of rusticles, and the orange goethite (α-Fe(O)OH) occurs internally in rusticles.
When Fe₂O₃·H₂O is heated, it loses its water of hydration. Further heating at 1670 K converts Fe₂O₃ to black Fe₃O₄ (Fe^IIFe^III₂O₄), which is known as the mineral magnetite.
Fe(O)OH is soluble in acids, giving [Fe(H₂O)₆]³⁺. In concentrated aqueous alkali, Fe₂O₃ gives [Fe(OH)₆]³⁻.^[13]

Reactions[edit]

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.^[18]

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):^[19]

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)):^[19]

ZnO + Fe₂O₃ → Zn(FeO₂)₂

Preparation[edit]

Iron(III) oxide is a product of the oxidation of iron. It can be prepared in the laboratory by electrolyzing a solution of sodium bicarbonate, an inert electrolyte, with an iron anode:

4 Fe + 3 O₂ + 2 H₂O → 4 FeO(OH)

The resulting hydrated iron(III) oxide, written here as FeO(OH), dehydrates around 200 °C.^[19][20]

2 FeO(OH) → Fe₂O₃ + H₂O

Uses[edit]

Iron industry[edit]

The overwhelming application of iron(III) oxide is as the feedstock of the steel and iron industries, e.g. the production of iron, steel, and many alloys.^[20]

Polishing[edit]

A very fine powder of ferric oxide is known as «jeweler’s rouge», «red rouge», or simply rouge. It is used to put the final polish on metallic jewelry and lenses, and historically as a cosmetic. Rouge cuts more slowly than some modern polishes, such as cerium(IV) oxide, but is still used in optics fabrication and by jewelers for the superior finish it can produce. When polishing gold, the rouge slightly stains the gold, which contributes to the appearance of the finished piece. Rouge is sold as a powder, paste, laced on polishing cloths, or solid bar (with a wax or grease binder). Other polishing compounds are also often called «rouge», even when they do not contain iron oxide. Jewelers remove the residual rouge on jewelry by use of ultrasonic cleaning. Products sold as «stropping compound» are often applied to a leather strop to assist in getting a razor edge on knives, straight razors, or any other edged tool.

Pigment[edit]

Iron(III) oxide is also used as a pigment, under names «Pigment Brown 6», «Pigment Brown 7», and «Pigment Red 101».^[21] Some of them, e.g. Pigment Red 101 and Pigment Brown 6, are approved by the US Food and Drug Administration (FDA) for use in cosmetics. Iron oxides are used as pigments in dental composites alongside titanium oxides.^[22]

Hematite is the characteristic component of the Swedish paint color Falu red.

Magnetic recording[edit]

Iron(III) oxide was the most common magnetic particle used in all types of magnetic storage and recording media, including magnetic disks (for data storage) and magnetic tape (used in audio and video recording as well as data storage). Its use in computer disks was superseded by cobalt alloy, enabling thinner magnetic films with higher storage density.^[23]

Photocatalysis[edit]

α-Fe₂O₃ has been studied as a photoanode for solar water oxidation.^[24] However, its efficacy is limited by a short diffusion length (2–4 nm) of photo-excited charge carriers^[25] and subsequent fast recombination, requiring a large overpotential to drive the reaction.^[26] Research has been focused on improving the water oxidation performance of Fe₂O₃ using nanostructuring,^[24] surface functionalization,^[27] or by employing alternate crystal phases such as β-Fe₂O₃.^[28]

Medicine[edit]

Calamine lotion, used to treat mild itchiness, is chiefly composed of a combination of zinc oxide, acting as astringent, and about 0.5% iron(III) oxide, the product’s active ingredient, acting as antipruritic. The red color of iron(III) oxide is also mainly responsible for the lotion’s pink color.

See also[edit]

• Chalcanthum

References[edit]

External links[edit]

• NIOSH Pocket Guide to Chemical Hazards

Справочник содержит названия веществ и описания химических формул (в т.ч. структурные формулы и скелетные формулы).

---

Общее число найденных записей: 1.
Показано записей: 1.