 Introduction
Chromium
(Cr) is a metallic, steel-gray element. It is a
chemical element of the 6th group of the periodic
system with an atomic number of 24. The 26 isotopes
are known from 42Cr until 67Cr.
The 3 of these isotopes are stable: 52Cr,
53Cr and 54Cr. Chromium is
existing in nature in the form of chromite (FeCr2O4)
ore. The unique physical properties of chromium
and related alloys have found many applications
in modern industry.
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Atomic
weight
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51.996
amu
|
|
Atomic
radius (Goldschmid)
|
128
pm
|
|
Electronic
structure
|
[Ar]
3d5 4s1
|
|
Crystal
structure
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Body
centred cubic
|
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Oxidation
number
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2,
3, 6
|
|
Electronegativities
|
1.66
|
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Density
(20 °C)
|
7.1
g•cm-3
|
|
Melting
point
|
1857
°C
|
|
Boiling
point
|
2672
°C
|
|
Electrical
resistivity (20 °C)
|
13.2
μΩ•cm
|
|
Temperature
coefficient (0-100 °C)
|
0.00214
K-1
|
|
Coefficient
of termal expansion (0°C - 100°C)
|
7.2•10-6K-1
|
|
Latent
heat of evaporation
|
6580
J•g-1
|
|
Latent
heat of fusion
|
260
J•g-1
|
|
Thermal
conductivity (0-100 °C)
|
94
Wm-1K-1
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Special
features of Chromium
Chromium
is a bright, lustrous metal with good corrosion
resistance. The pure Chromium is a hard metal, melts
with difficulty, and has high polish. More than
half the production of chromium goes into metallic
products, and about another third is used in refractories.
The chief use of chromium is to form alloys with
iron, nickel, or cobalt. The addition of chromium
imparts hardness, strength, and corrosion resistance
to the alloy. In the stainless steels, chromium
makes up 10 percent or more of the final composition.
Because of its hardness, an alloy of chromium, cobalt,
and tungsten is used for high-speed metal-cutting
tools. When deposited electrolytically, chromium
provides a hard, corrosion-resistant, lustrous finish.
For this reason it is widely used as body trim on
automobiles and other vehicles. The extensive use
of chromite as a refractory is based on its high
melting point, its moderate thermal expansion, and
the stability of its crystalline structure. In chromites
and chromic salts, chromium has a valence of +3.
Most of these compounds are green, but some are
red or blue. Chromic oxide (Cr2O3) is a green solid.
In chromates and dichromates, chromium has a valence
of +6. Potassium dichromate (K2Cr2O7) is a red,
water-soluble solid that, mixed with gelatin, gives
a light-sensitive surface useful in photographic
processes. The chromates are generally yellow, the
best known being lead chromate (PbCrO4), an insoluble
solid widely used as a pigment called chrome yellow.
Chrome green is a mixture of chrome yellow and Prussian
blue. Chromium gives glass an emerald green color
and is widely used as a catalyst. Also Chromium
is an ingredient in several important catalysts.
Advantages
- Chromium
excellent withstands corrosion;
- Chromium
can withstand many acids;
- Chromium
has a high melting point;
- Chromium
has high stability of its crystalline structure;
- Chromium
is a excellent component for corrosion steadfast
alloys;
Applications
- Chromium
uses in metal industry: it is an alloying
agent for alloys to increase corrosion resistance; for
alloying with nickel in the manufacture
of heat resisting alloys; for alloying
with iron, or nickel and iron, to produce
stainless and heat resistant steels; for
chrome plating; for anodizing aluminium;
- Chromium
uses as material for production of the dyes;
- Chromium
uses for catalyst.
Flokal
can provide the Chromium alloys:
We
manufacture special chromium alloys (CrFe, CrNi,
Cr0.4La2O3) with
certain physical properties (higher strength, higher
temperature of usage, etc.) compared to pure Chromium.
These alloys have some advantages and respective
applications in high temperature cells, design of
chemical devices, the sputtering technology.
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