should be known,
On this page :
- Molybdenum and
ceramics, general information (Technological
article by Smart.Conseil)
Use in Crystalline
introduction (Toxicological article by Edouard
and Environnemental Exposure
- Translated by
- Edouard Bastarache
M.D. (Occupational & Environmental
- Author of "
Substitutions for raw ceramic materials "
- Sorel-Tracy -
Quebec - Canada
- Symbol: Mo (atomic number
- Atomic weight : 95.94 g
- Melting point : 2622 °C
- Boiling point : 4825
- Produced by reduction of
molybdic oxide (MoO3)
- Molybdenum oxidizes easily
in air when heated to red, it is the same for the
sulphide of molybdenum (Molybdenite).
- Natural ore: molybdenum
sulfide or molybdenite, MoS2.
- Oxide form (IV) : MoO3,
molar mass 143.94 g/mol
- Melting point of the oxide
MoO3 is close to 796°C.
- MoO3, slightly soluble in
cold water, is very soluble when hot. It easily forms
insoluble molybdates with alkaline-earth and basic
- Molybdic acid, MoO3,H2O (or
MoO4H2), is the product formed by the contact of MoO3
with water. Unstable, this product is dehydrated by
- Molybdenum chloride (III),
- Molybdenum chloride (V),
- Molybdenum oxide (VI), MoO3
(molybdenum trioxyde or molybdic anhydride)
- Molybdenum sulphide (IV),
MoS2 (Molybdenite): melting point 1185°C,
decomposes in air above red heat.
- Ammonium molybdate
tetrahydrate, Mo7O24(NH4)6,4H2O: This product breaks
up under the action of heat into MoO3 and MoO2 in an
air-poor atmosphere. It is soluble in water
- Barium molybdate, BaMoO4: a
member of water-insoluble molybdates. Melting point in
the vicinity of 1380 C.
- Calcium molybdate, CaMoO4: a
member of water-insoluble molybdates.
- Lead molybdate, PbMoO4: a
member of water-insoluble molybdates. Melting point
1084°C. Sodium molybdate, Na2MoO4: Soluble in
water. Melting point : 706°C.
- Can be used as an
electrolyte for deflocculation.
Colouring Materials :
- Molybdenum-Alumina Gray
(Mo-Al) : made with calcined mixtures of molybdenum
oxide and alumina (with also sometimes zinc oxide or
tin dioxide). Great stability in oxidation firing or
in light redution, these colouring materials can stand
up to1400°C. Little recommended for use in
glazes, they are primarily used for colouring slips
- Example of a
Molybdenum-Alumina-Zinc Gray composition
- Zinc oxide (ZnO) 12
- Alumina calcine (Al2O3) 55
- Molybdenum oxide (MoO3) 33
- Calcine near 1260°C
- Use in
Crystalline Glazes :
- Molybdenum added in small
amounts (0.1 to 0.3 %) decreases the number of
crystals but increases their size. It rather easily
forms crystals with plombous bases (0.40 to 0.55 mole
of PbO) and gives molybdates (wulfenite type, PbMoO4)
not coloured and made iridescent
- Molybdenum belongs to oxides
which favor the formation of crystals by their
capacity for nucleation and allows them a good growth.
It strongly lowers surface tension of glazes for weak
additions from 0.2%. Molybdenum volitilizes rather
easily as low as 800°C, which makes its use
awkward in the event of firing other glazes sensitive
to molybdenum (unless it is the desired effect,
consisting in obtaining a surface crystallization by
volatile molybdenum deposit).
for kilns :
- Molybdenum silicide (or also
called disilicide), MoSi2, has a melting point higher
than 3700°C, it is a ceramics-metal or "Cermet"*.
It is used to make electric resistors in certain kilns
for firing ceramic wares at very high temperature (up
- (*): Cermet (a contraction
of Ceramics-Metal ), a product combining resistance to
oxidation and deformation of ceramic products with the
conductibility, ductibility and resistance to thermal
shocks of metals.
- These products are developed
by sintering of prepared powders and shaped according
to various processes among which extrusion,
but also call upon more advanced
techniques such as impregnation.
surface-active agent :
- Molybdenum oxide, MoO3, is
used as a wetting agent to reduce surface tension when
hot. The amounts used, small, are of the order of 0.1
to 0.3 %. In higher proportions, up to 1-1.2 %, it
allows binding to surfaces difficult to enamel such as
- It is, just as basic and
alkaline-earth molybdates, mainly used as a wetting
and binding agent in cast iron and iron/steel sheet
/ november 2002
- Molybdenum trioxide (MoO3)
is used in ceramics as a colorant to produce yellowish
and yellow green colors.
- Molybdenum is obtained from
such ores as :
and Environmental Exposure :
- Common uses of molybdenum
- -metallurgy, such as its use
- -as a catalyst for the
- -as a pigment.
- Exposure commonly occurs
during the liberation of dust from mining and the
processing of ore, from the grinding of metals or
alloys, from oxyacetylene cutting, and from dust from
its various compounds.
- I-Solubility Factor
- A - Insoluble
molybdenum compounds include :
- -molybdenum disulfide
- -lead molybdate
- -calcium molybdate
- B - Soluble compounds
- -molybdenum trioxide
- -ammonium paramolybdate
- -sodium molybdate dihydrate
- II-Routes of Exposure
- Exposure to molybdenum and
related compounds usually occurs via inhalation of
dust. If these compounds are water-soluble, absorption
is increased, and toxicity may be greater than that
from non-water-soluble compounds.
- Gastrointestinal absorption
is approximately 50% of an ingested amount and depends
on the water solubility of the compound
Metabolism, and Elimination :
- Molybdenum is present in
humans, with an average adult content of 9
- Human whole blood levels
average approximately 5 ng per ml.
- It is contained principally
- -adrenal glands;
- More than 50% of molybdenum
is excreted primarely through the kidneys.
Approximately 6% is excreted through the bile when
excess molybdenum is present.
- IV-Signs, Symptoms, and
- A-Acute Toxicity
- Molybdenum products may
cause toxicity in humans, but adequate studies
reporting such effects are lacking.
- The high prevalence of
articular effects in Armenian villages was associated
with a significant ingestion of molybdenum, which
caused a disorder of the metabolism of uric
- Workers involved in
producing molybdenum oxide have demonstrated a higher
rate of :
- -aching joints;
- -non-specific skin and hair
- Molybdenum trioxide may
cause irritation to mucous membranes (eyes, nose,
- Exposure to molybdenum dust
causes an increase in serum uric acid and
- B-Chronic Toxicity
- Data are extremely limited
in regard to chronic toxicity from molybdenum and its
compounds. Molybdenum may cause a pneumoconiosis in
susceptible individuals, but definitive data are
- V-Management of Toxicity
or Exposure :
- Persons exposed to hazardous
concentrations of molybdenum should be removed from
further exposure. Treatment is symptomatic, and no
specific therapy is available for removal of
molybdenum from tissues. Treatment of joint complaints
- 1-Medical and Biological
- Laboratory measurements of
serum and urinary molybdenum levels may be performed,
but levels do not correlate with signs and symptoms.
Serum uric acid and ceruloplasmin may be
- 2-Exposure Controls
- Prevention of exposure is
the mainstay in preventing toxicity, including good
process enclosures with general dilution ventilation
and local exhaust ventilation. NIOSH and OSHA
recommend that workers exposed to insoluble molybdenum
compounds wear personal protective equipment designed
to limit dust, mist, or fume inhalation.
- Workers exposed to soluble
compounds need impervious clothing, gloves, face
shields, and other appropriate clothing as necessary
to prevent skin contact.
- However, no data are
available regarding skin effects or clinical effects
from this route of absorption.
- 3-Exposure Limits
- In Quebec, the VEMP (Valeur
d'Exposition Moyenne Pondérée) is
- 1 - Insoluble
compounds : 10 mg/m3 (as Mo)
- 2 - Soluble compounds
: 5 mg/m3 (as Mo).
- Good house keeping of your
studio is very important; to do so you may, among
other things, use wet processes, or even a vacuum
system whose air is exhausted outside of the
- Avoidance of processes
generating unnecessary dust is also important.
- According to the severity of
exposure, the preventive measures proposed by NIOSH
and OSHA should be applied.
- 1-Clinical Environmental
Health and Toxic Exposures, Sullivan & Krieger;
Industrielle et Intoxications Professionnelles,
Lauwerys R. last edition.
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