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= Vanadium =
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Introduction
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Vanadium is a chemical element; it has symbol V and atomic number 23.
It is a hard, silvery-grey, malleable transition metal. The elemental
metal is rarely found in nature, but once isolated artificially, the
formation of an oxide layer (passivation) somewhat stabilizes the free
metal against further oxidation.
Spanish-Mexican scientist Andrés Manuel del Río discovered compounds
of vanadium in 1801 by analyzing a new lead-bearing mineral he called
"brown lead". Though he initially presumed its qualities were due to
the presence of a new element, he was later erroneously convinced by
French chemist Hippolyte Victor Collet-Descotils that the element was
just chromium. Then in 1830, Nils Gabriel Sefström generated chlorides
of vanadium, thus proving there was a new element, and named it
"vanadium" after the Scandinavian goddess of beauty and fertility,
Vanadís (Freyja). The name was based on the wide range of colors found
in vanadium compounds. Del Río's lead mineral was ultimately named
vanadinite for its vanadium content. In 1867, Henry Enfield Roscoe
obtained the pure element.
Vanadium occurs naturally in about 65 minerals and fossil fuel
deposits. It is produced in China and Russia from steel smelter slag.
Other countries produce it either from magnetite directly, flue dust
of heavy oil, or as a byproduct of uranium mining. It is mainly used
to produce specialty steel alloys such as high-speed tool steels, and
some aluminium alloys. The most important industrial vanadium
compound, vanadium pentoxide, is used as a catalyst for the production
of sulfuric acid. The vanadium redox battery for energy storage may be
an important application in the future.
Large amounts of vanadium ions are found in a few organisms, possibly
as a toxin. The oxide and some other salts of vanadium have moderate
toxicity. Particularly in the ocean, vanadium is used by some life
forms as an active center of enzymes, such as the vanadium
bromoperoxidase of some ocean algae.
History
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Vanadium was discovered in Mexico in 1801 by the Spanish mineralogist
Andrés Manuel del Río. Del Río extracted the element from a sample of
Mexican "brown lead" ore, later named vanadinite. He found that its
salts exhibit a wide variety of colors, and as a result, he named the
element 'panchromium' (Greek: παγχρώμιο "all colors"). Later, del Río
renamed the element 'erythronium' (Greek: ερυθρός "red") because most
of the salts turned red upon heating. In 1805, French chemist
Hippolyte Victor Collet-Descotils, backed by del Río's friend Baron
Alexander von Humboldt, incorrectly declared that del Río's new
element was an impure sample of chromium. Del Río accepted
Collet-Descotils' statement and retracted his claim.
In 1831 Swedish chemist Nils Gabriel Sefström rediscovered the element
in a new oxide he found while working with iron ores. Later that year,
Friedrich Wöhler confirmed that this element was identical to that
found by del Río and hence confirmed del Río's earlier work. Sefström
chose a name beginning with V, which had not yet been assigned to any
element. He called the element 'vanadium' after Old Norse 'Vanadís'
(another name for the Norse Vanir goddess Freyja, whose attributes
include beauty and fertility), because of the many beautifully colored
chemical compounds it produces. On learning of Wöhler's findings, del
Río began to passionately argue that his old claim be recognized, but
the element kept the name 'vanadium'. In 1831, the geologist George
William Featherstonhaugh suggested that vanadium should be renamed
"'rionium'" after del Río, but this suggestion was not followed.
As vanadium is usually found combined with other elements, the
isolation of vanadium metal was difficult. In 1831, Berzelius reported
the production of the metal, but Henry Enfield Roscoe showed that
Berzelius had produced the nitride, vanadium nitride (VN). Roscoe
eventually produced the metal in 1867 by reduction of vanadium(II)
chloride, VCl2, with hydrogen. In 1927, pure vanadium was produced by
reducing vanadium pentoxide with calcium.
The first large-scale industrial use of vanadium was in the steel
alloy chassis of the Ford Model T, inspired by French race cars.
Vanadium steel allowed reduced weight while increasing tensile
strength (). For the first decade of the 20th century, most vanadium
ore were mined by the American Vanadium Company from the Minas Ragra
in Peru. Later, the demand for uranium rose, leading to increased
mining of that metal's ores. One major uranium ore was carnotite,
which also contains vanadium. Thus, vanadium became available as a
by-product of uranium production. Eventually, uranium mining began to
supply a large share of the demand for vanadium.
In 1911, German chemist Martin Henze discovered vanadium in the
hemovanadin proteins found in blood cells (or coelomic cells) of
Ascidiacea (sea squirts).
Characteristics
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Vanadium is an average-hard, ductile, steel-blue metal. Vanadium is
usually described as "soft", because it is ductile, malleable, and not
brittle. Vanadium is harder than most metals and steels (see
Hardnesses of the elements (data page) and iron). It has good
resistance to corrosion and it is stable against alkalis and sulfuric
and hydrochloric acids. It is oxidized in air at about 933 K (660 °C,
1220 °F), although an oxide passivation layer forms even at room
temperature. It also reacts with hydrogen peroxide.
Isotopes
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Naturally occurring vanadium is composed of one stable isotope, 51V,
and one radioactive isotope, 50V. The latter has a half-life of
2.71×1017 years and a natural abundance of 0.25%. 51V has a nuclear
spin of , which is useful for NMR spectroscopy. Twenty-four artificial
radioisotopes have been characterized, ranging in mass number from 40
to 65. The most stable of these isotopes are 49V with a half-life of
330 days, and 48V with a half-life of 16.0 days. The remaining
radioactive isotopes have half-lives shorter than an hour, most below
10 seconds. At least four isotopes have metastable excited states.
Electron capture is the main decay mode for isotopes lighter than 51V.
For the heavier ones, the most common mode is beta decay. The electron
capture reactions lead to the formation of element 22 (titanium)
isotopes, while beta decay leads to element 24 (chromium) isotopes.
Compounds
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The chemistry of vanadium is noteworthy for the accessibility of the
four adjacent oxidation states 2-5. In an aqueous solution, vanadium
forms metal aquo complexes of which the colors are lilac [V(H2O)6]2+,
green [V(H2O)6]3+, blue [VO(H2O)5]2+, yellow-orange oxides
[VO(H2O)5]3+, the formula for which depends on pH. Vanadium(II)
compounds are reducing agents, and vanadium(V) compounds are oxidizing
agents. Vanadium(IV) compounds often exist as vanadyl derivatives,
which contain the VO2+ center.
Ammonium vanadate(V) (NH4VO3) can be successively reduced with
elemental zinc to obtain the different colors of vanadium in these
four oxidation states. Lower oxidation states occur in compounds such
as V(CO)6, and substituted derivatives.
Vanadium pentoxide is a commercially important catalyst for the
production of sulfuric acid, a reaction that exploits the ability of
vanadium oxides to undergo redox reactions.
The vanadium redox battery utilizes all four oxidation states: one
electrode uses the +5/+4 couple and the other uses the +3/+2 couple.
Conversion of these oxidation states is illustrated by the reduction
of a strongly acidic solution of a vanadium(V) compound with zinc dust
or amalgam. The initial yellow color characteristic of the pervanadyl
ion [VO2(H2O)4]+ is replaced by the blue color of [VO(H2O)5]2+,
followed by the green color of [V(H2O)6]3+ and then the violet color
of [V(H2O)6]2+. Another potential vanadium battery based on VB2 uses
multiple oxidation state to allow for 11 electrons to be released per
VB2, giving it higher energy capacity by order of compared to Li-ion
and gasoline per unit volume. VB2 batteries can be further enhanced as
air batteries, allowing for even higher energy density and lower
weight than lithium battery or gasoline, even though recharging
remains a challenge.
Oxyanions
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In an aqueous solution, vanadium(V) forms an extensive family of
oxyanions as established by 51V NMR spectroscopy. The
interrelationships in this family are described by the predominance
diagram, which shows at least 11 species, depending on pH and
concentration. The tetrahedral orthovanadate ion, , is the principal
species present at pH 12-14. Similar in size and charge to
phosphorus(V), vanadium(V) also parallels its chemistry and
crystallography. Orthovanadate V is used in protein crystallography to
study the biochemistry of phosphate. Besides that, this anion also has
been shown to interact with the activity of some specific enzymes. The
tetrathiovanadate [VS4]3− is analogous to the orthovanadate ion.
At lower pH values, the monomer [HVO4]2− and dimer [V2O7]4− are
formed, with the monomer predominant at a vanadium concentration of
less than c. 10−2M (pV > 2, where pV is equal to the minus value of
the logarithm of the total vanadium concentration/M). The formation of
the divanadate ion is analogous to the formation of the dichromate
ion. As the pH is reduced, further protonation and condensation to
polyvanadates occur: at pH 4-6 [H2VO4]− is predominant at pV greater
than ca. 4, while at higher concentrations trimers and tetramers are
formed. Between pH 2-4 decavanadate predominates, its formation from
orthovanadate is represented by this condensation reaction:
:10 [VO4]3− + 24 H+ → [V10O28]6− + 12 H2O
In decavanadate, each V(V) center is surrounded by six oxide ligands.
Vanadic acid, H3VO4, exists only at very low concentrations because
protonation of the tetrahedral species [H2VO4]− results in the
preferential formation of the octahedral [VO2(H2O)4]+ species. In
strongly acidic solutions, pH < 2, [VO2(H2O)4]+ is the predominant
species, while the oxide V2O5 precipitates from solution at high
concentrations. The oxide is formally the acid anhydride of vanadic
acid. The structures of many vanadate compounds have been determined
by X-ray crystallography.
Vanadium(V) forms various peroxo complexes, most notably in the active
site of the vanadium-containing bromoperoxidase enzymes. The species
VO(O2)(H2O)4+ is stable in acidic solutions. In alkaline solutions,
species with 2, 3 and 4 peroxide groups are known; the last forms
violet salts with the formula M3V(O2)4 nH2O (M= Li, Na, etc.), in
which the vanadium has an 8-coordinate dodecahedral structure.
Halide derivatives
====================
Twelve binary halides, compounds with the formula VXn (n=2..5), are
known. VI4, VCl5, VBr5, and VI5 do not exist or are extremely
unstable. In combination with other reagents, VCl4 is used as a
catalyst for the polymerization of dienes. Like all binary halides,
those of vanadium are Lewis acidic, especially those of V(IV) and
V(V). Many of the halides form octahedral complexes with the formula
VX'n'L6−'n' (X= halide; L= other ligand).
Many vanadium oxyhalides (formula VOmXn) are known. The oxytrichloride
and oxytrifluoride (VOCl3 and VOF3) are the most widely studied. Akin
to POCl3, they are volatile, adopt tetrahedral structures in the gas
phase, and are Lewis acidic.
Coordination compounds
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Complexes of vanadium(II) and (III) are reducing, while those of V(IV)
and V(V) are oxidants. The vanadium ion is rather large and some
complexes achieve coordination numbers greater than 6, as is the case
in [V(CN)7]4−. Oxovanadium(V) also forms 7 coordinate coordination
complexes with tetradentate ligands and peroxides and these complexes
are used for oxidative brominations and thioether oxidations. The
coordination chemistry of V4+ is dominated by the vanadyl center,
VO2+, which binds four other ligands strongly and one weakly (the one
trans to the vanadyl center). An example is vanadyl acetylacetonate
(V(O)(O2C5H7)2). In this complex, the vanadium is 5-coordinate,
distorted square pyramidal, meaning that a sixth ligand, such as
pyridine, may be attached, though the association constant of this
process is small. Many 5-coordinate vanadyl complexes have a trigonal
bipyramidal geometry, such as VOCl2(NMe3)2. The coordination chemistry
of V5+ is dominated by the relatively stable dioxovanadium
coordination complexes which are often formed by aerial oxidation of
the vanadium(IV) precursors indicating the stability of the +5
oxidation state and ease of interconversion between the +4 and +5
states.
Organometallic compounds
==========================
The organometallic chemistry of vanadium is welldeveloped. Vanadocene
dichloride is a versatile starting reagent and has applications in
organic chemistry. Vanadium carbonyl, V(CO)6, is a rare example of a
paramagnetic metal carbonyl. Reduction yields V (isoelectronic with
Cr(CO)6), which may be further reduced with sodium in liquid ammonia
to yield V (isoelectronic with Fe(CO)5).
Occurrence
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Metallic vanadium is rare in nature (known as native vanadium), having
been found among fumaroles of the Colima Volcano, but vanadium
compounds occur naturally in about 65 different minerals.
Vanadium began to be used in the manufacture of special steels in
1896. At that time, very few deposits of vanadium ores were known.
Between 1899 and 1906, the main deposits exploited were the mines of
Santa Marta de los Barros (Badajoz), Spain. Vanadinite was extracted
from these mines. At the beginning of the 20th century, a large
deposit of vanadium ore was discovered near Junín, Cerro de Pasco,
Peru (now the Minas Ragra vanadium mine). For several years this
patrónite (VS4) deposit was an economically significant source for
vanadium ore. In 1920 roughly two-thirds of the worldwide production
was supplied by the mine in Peru. With the production of uranium in
the 1910s and 1920s from carnotite () vanadium became available as a
side product of uranium production. Vanadinite () and other vanadium
bearing minerals are only mined in exceptional cases. With the rising
demand, much of the world's vanadium production is now sourced from
vanadium-bearing magnetite found in ultramafic gabbro bodies. If this
titanomagnetite is used to produce iron, most of the vanadium goes to
the slag and is extracted from it.
Vanadium is mined mostly in China, South Africa and eastern Russia. In
2022 these three countries mined more than 96% of the 100,000 tons of
produced vanadium, with China providing 70%.
Fumaroles of Colima are known of being vanadium-rich, depositing other
vanadium minerals, that include shcherbinaite (V2O5) and colimaite
(K3VS4).
Vanadium is also present in bauxite and deposits of crude oil, coal,
oil shale, and tar sands. In crude oil, concentrations up to 1200 ppm
have been reported. When such oil products are burned, traces of
vanadium may cause corrosion in engines and boilers. An estimated
110,000 tons of vanadium per year are released into the atmosphere by
burning fossil fuels. Black shales are also a potential source of
vanadium. During WWII some vanadium was extracted from alum shales in
the south of Sweden.
In the universe, the cosmic abundance of vanadium is 0.0001%, making
the element nearly as common as copper or zinc. Vanadium is the 19th
most abundant element in the crust. It is detected spectroscopically
in light from the Sun and sometimes in the light from other stars. The
vanadyl ion is also abundant in seawater, having an average
concentration of 30 nM (1.5 mg/m3). Some mineral water springs also
contain the ion in high concentrations. For example, springs near
Mount Fuji contain as much as 54 μg per liter.
Production
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Vanadium metal is obtained by a multistep process that begins with
roasting crushed ore with NaCl or Na2CO3 at about 850 °C to give
sodium metavanadate (NaVO3). An aqueous extract of this solid is
acidified to produce "red cake", a polyvanadate salt, which is reduced
with calcium metal. As an alternative for small-scale production,
vanadium pentoxide is reduced with hydrogen or magnesium. Many other
methods are also used, in all of which vanadium is produced as a
byproduct of other processes. Purification of vanadium is possible by
the crystal bar process developed by Anton Eduard van Arkel and Jan
Hendrik de Boer in 1925. It involves the formation of the metal
iodide, in this example vanadium(III) iodide, and the subsequent
decomposition to yield pure metal:
:2 V + 3 I2 2 VI3
Most vanadium is used as a steel alloy called ferrovanadium.
Ferrovanadium is produced directly by reducing a mixture of vanadium
oxide, iron oxides and iron in an electric furnace. The vanadium ends
up in pig iron produced from vanadium-bearing magnetite. Depending on
the ore used, the slag contains up to 25% of vanadium.
Alloys
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Approximately 85% of the vanadium produced is used as ferrovanadium or
as a steel additive. The considerable increase of strength in steel
containing small amounts of vanadium was discovered in the early 20th
century. Vanadium forms stable nitrides and carbides, resulting in a
significant increase in the strength of steel. From that time on,
vanadium steel was used for applications in axles, bicycle frames,
crankshafts, gears, and other critical components. There are two
groups of vanadium steel alloys. Vanadium high-carbon steel alloys
contain 0.15-0.25% vanadium, and high-speed tool steels (HSS) have a
vanadium content of 1-5%. For high-speed tool steels, a hardness above
HRC 60 can be achieved. HSS steel is used in surgical instruments and
tools. Powder-metallurgic alloys contain up to 18% percent vanadium.
The high content of vanadium carbides in those alloys increases wear
resistance significantly. One application for those alloys is tools
and knives.
Vanadium stabilizes the beta form of titanium and increases the
strength and temperature stability of titanium. Mixed with aluminium
in titanium alloys, it is used in jet engines, high-speed airframes
and dental implants. The most common alloy for seamless tubing is
Titanium 3/2.5 containing 2.5% vanadium, the titanium alloy of choice
in the aerospace, defense, and bicycle industries. Another common
alloy, primarily produced in sheets, is Titanium 6AL-4V, a titanium
alloy with 6% aluminium and 4% vanadium.
Several vanadium alloys show superconducting behavior. The first A15
phase superconductor was a vanadium compound, V3Si, which was
discovered in 1952. Vanadium-gallium tape is used in superconducting
magnets (17.5 teslas or 175,000 gauss). The structure of the
superconducting A15 phase of V3Ga is similar to that of the more
common Nb3Sn and Nb3Ti.
It has been found that a small amount, 40 to 270 ppm, of vanadium in
Wootz steel significantly improved the strength of the product, and
gave it the distinctive patterning. The source of the vanadium in the
original Wootz steel ingots remains unknown.
Vanadium can be used as a substitute for molybdenum in armor steel,
though the alloy produced is far more brittle and prone to spalling on
non-penetrating impacts. Nazi Germany was one of the most prominent
users of such alloys, in armored vehicles like Tiger II or Jagdtiger.
Catalysts
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Vanadium compounds are used extensively as catalysts; Vanadium
pentoxide V2O5, is used as a catalyst in manufacturing sulfuric acid
by the contact process In this process sulfur dioxide () is oxidized
to the trioxide (): In this redox reaction, sulfur is oxidized from +4
to +6, and vanadium is reduced from +5 to +4:
:V2O5 + SO2 → 2 VO2 + SO3
The catalyst is regenerated by oxidation with air:
:4 VO2 + O2 → 2 V2O5
Similar oxidations are used in the production of maleic anhydride:
:C4H10 + 3.5 O2 → C4H2O3 + 4 H2O
Phthalic anhydride and several other bulk organic compounds are
produced similarly. These green chemistry processes convert
inexpensive feedstocks to highly functionalized, versatile
intermediates.
Vanadium is an important component of mixed metal oxide catalysts used
in the oxidation of propane and propylene to acrolein, acrylic acid or
the ammoxidation of propylene to acrylonitrile.
Other uses
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The vanadium redox battery, a type of flow battery, is an
electrochemical cell consisting of aqueous vanadium ions in different
oxidation states. Batteries of this type were first proposed in the
1930s and developed commercially from the 1980s onwards. Cells use +5
and +2 formal oxidization state ions. Vanadium redox batteries are
used commercially for grid energy storage.
Vanadate can be used for protecting steel against rust and corrosion
by conversion coating. Vanadium foil is used in cladding titanium to
steel because it is compatible with both iron and titanium. The
moderate thermal neutron-capture cross-section and the short half-life
of the isotopes produced by neutron capture makes vanadium a suitable
material for the inner structure of a fusion reactor.
Vanadium can be added in small quantities < 5% to LFP battery
cathodes to increase ionic conductivity.
Proposed
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Lithium vanadium oxide has been proposed for use as a
high-energy-density anode for lithium-ion batteries, at 745 Wh/L when
paired with a lithium cobalt oxide cathode. Vanadium phosphates have
been proposed as the cathode in the lithium vanadium phosphate
battery, another type of lithium-ion battery.
Biological role
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Vanadium has a more significant role in marine environments than
terrestrial ones.
Vanadoenzymes
===============
Several species of marine algae produce vanadium bromoperoxidase as
well as the closely related chloroperoxidase (which may use a heme or
vanadium cofactor) and iodoperoxidases. The bromoperoxidase produces
an estimated 1-2 million tons of bromoform and 56,000 tons of
bromomethane annually. Most naturally occurring organobromine
compounds are produced by this enzyme, catalyzing the following
reaction (R-H is hydrocarbon substrate):
A vanadium nitrogenase is used by some nitrogen-fixing
micro-organisms, such as 'Azotobacter'. In this role, vanadium serves
in place of the more common molybdenum or iron, and gives the
nitrogenase slightly different properties.
Vanadium accumulation in tunicates
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Vanadium is essential to tunicates, where it is stored in the highly
acidified vacuoles of certain blood cell types, designated
vanadocytes. Vanabins (vanadium-binding proteins) have been identified
in the cytoplasm of such cells. The concentration of vanadium in the
blood of ascidian tunicates is as much as ten million times higher
than the surrounding seawater, which normally contains 1 to 2 μg/L.
The function of this vanadium concentration system and these
vanadium-bearing proteins is still unknown, but the vanadocytes are
later deposited just under the outer surface of the tunic, where they
may deter predation.
Fungi
=======
'Amanita muscaria' and related species of macrofungi accumulate
vanadium (up to 500 mg/kg in dry weight). Vanadium is present in the
coordination complex amavadin in fungal fruit-bodies. The biological
importance of the accumulation is unknown. Toxic or peroxidase enzyme
functions have been suggested.
Mammals
=========
Deficiencies in vanadium result in reduced growth in rats. The U.S.
Institute of Medicine has not confirmed that vanadium is an essential
nutrient for humans, so neither a Recommended Dietary Intake nor an
Adequate Intake have been established. Dietary intake is estimated at
6 to 18 μg/day, with less than 5% absorbed. The Tolerable Upper Intake
Level (UL) of dietary vanadium, beyond which adverse effects may
occur, is set at 1.8 mg/day.
Research
==========
Vanadyl sulfate as a dietary supplement has been researched as a means
of increasing insulin sensitivity or otherwise improving glycemic
control in people who are diabetic. Some of the trials had significant
treatment effects but were deemed as being of poor study quality. The
amounts of vanadium used in these trials (30 to 150 mg) far exceeded
the safe upper limit. The conclusion of the systemic review was "There
is no rigorous evidence that oral vanadium supplementation improves
glycaemic control in type 2 diabetes. The routine use of vanadium for
this purpose cannot be recommended."
In astrobiology, it has been suggested that discrete vanadium
accumulations on Mars could be a potential microbial biosignature when
used in conjunction with Raman spectroscopy and morphology.
Safety
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All vanadium compounds should be considered toxic. Tetravalent VOSO4
has been reported to be at least 5 times more toxic than trivalent
V2O3. The US Occupational Safety and Health Administration (OSHA) has
set an exposure limit of 0.05 mg/m3 for vanadium pentoxide dust and
0.1 mg/m3 for vanadium pentoxide fumes in workplace air for an 8-hour
workday, 40-hour work week. The US National Institute for Occupational
Safety and Health (NIOSH) has recommended that 35 mg/m3 of vanadium be
considered immediately dangerous to life and health, that is, likely
to cause permanent health problems or death.
Vanadium compounds are poorly absorbed through the gastrointestinal
system. Inhalation of vanadium and vanadium compounds results
primarily in adverse effects on the respiratory system. Quantitative
data are, however, insufficient to derive a subchronic or chronic
inhalation reference dose. Other effects have been reported after oral
or inhalation exposures on blood parameters, liver, neurological
development, and other organs in rats.
There is little evidence that vanadium or vanadium compounds are
reproductive toxins or teratogens. Vanadium pentoxide was reported to
be carcinogenic in male rats and in male and female mice by inhalation
in an NTP study, although the interpretation of the results has been
disputed a few years after the report. The carcinogenicity of vanadium
has not been determined by the United States Environmental Protection
Agency.
Vanadium traces in diesel fuels are the main fuel component in high
temperature corrosion. During combustion, vanadium oxidizes and reacts
with sodium and sulfur, yielding vanadate compounds with melting
points as low as , which attack the passivation layer on steel and
render it susceptible to corrosion. The solid vanadium compounds also
abrade engine components.
External links
======================================================================
*
*[
http://www.periodicvideos.com/videos/023.htm Vanadium] at 'The
Periodic Table of Videos' (University of Nottingham)
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=========
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Original Article:
http://en.wikipedia.org/wiki/Vanadium
