- Lead tetroxide
ImageFile = Red lead.jpg
ImageSize = 250px
ImageName = Red lead powder
IUPACName = dilead(II) lead(IV) oxide
Section1 = Chembox Identifiers
CASNo = 1314-41-6
Section2 = Chembox Properties
Formula = Pb3O4 2PbO.PbO2
MolarMass = 685.598 g/mol
Appearance = orange red powder
Density = 8.3 g/cm3
MeltingPt = 500°C
Section3 = Chembox Hazards
Red lead, also called minium, lead tetroxide or triplumbic tetroxide, is a bright red or orange
crystallineor amorphous pigment. Its Latinname "minium" originates from the Minius Riverin northwest Spainwhere it was first mined. Natural minium is uncommon, forming only in extreme oxidizing conditions of lead ore bodies. The best specimens known come from Broken Hill, New South Wales, Australia, where they formed as the result of a mine fire [ [http://www.galleries.com/minerals/oxides/minium/minium.htm Minium] ] . A map and list of known occurrences is available [http://www.mindat.org/show.php?id=2721&ld=1#themap here] .
The melting point of lead tetroxide is 500 °C, at which it decomposes to
lead(II) oxideand oxygen.
Red lead is virtually insoluble in water. However, it is soluble in
hydrochloric acidpresent in the stomach, and therefore it is toxicwhen ingested. It is also insoluble in alcohol. It dissolves in hydrochloric acid, glacial acetic acid, and diluted mixture of nitric acidand hydrogen peroxide.
Lead tetroxide is prepared by
calcinationof lead(II) oxide(also called litharge) in air at about 450 to 480 °C:: 6 PbO + O2 → 2 Pb3O4The resulting material is contaminated with lead(II) oxide. If a pure compound is desired, PbO can be removed by a potassium hydroxidesolution:: PbO + KOH + H2O → K [Pb(OH)3] (aq)
Another method of preparation relies on annealing of
lead carbonate( cerussite) in air:: 6 PbCO3 + O2 → 2 Pb3O4 + 6 CO2
Yet another method is oxidative annealing of
lead white:: 3 Pb2CO3(OH)2 + O2 → 2 Pb3O4 + 3 CO2 + 3 H2O
In solution, lead tetroxide can be prepared eg. by reaction of
potassium plumbatewith lead acetate:: K2PbO3 + 2 Pb(OCOCH3)2 + H2O → Pb3O4 + 2 KOCOCH3 + 2 CH3COOHyielding yellow insoluble lead tetroxide monohydrate, Pb3O4.H2O, which can be turned into the anhydrous form by gentle heating.
With iron oxides and with elementary
iron, lead tetroxide forms insoluble iron(II) and iron(III) plumbates, which is the basis of the anti-corrosive properties of lead-based paints applied to iron objects.
When heated to 500 °C, it decomposes to lead(II) oxide and oxygen. At 580 °C, the reaction is complete.: 2 Pb3O4 → 6 PbO + O2
Nitric aciddissolves the lead(II) oxide component, leaving behind the insoluble lead(IV) oxide:: Pb3O4 + 4 HNO3 → PbO2 + 2 Pb(NO3)2 + 2 H2O
Lead tetroxide is most often used as a
pigmentfor undercoat paints for ironobjects. Due to its toxicityits use is being limited. In past it was used in combination with linseed oil as a thick, long-protecting anticorrosive paint. Also combination of minium and linen fibres was used for plumbing, now replaced with PTFE tape. Currently it is mostly used for manufacture of glass, especially lead glass. It finds limited use in some amateur pyrotechnicsas a relatively potent oxidizer.
When breathed in, lead tetroxide irritates lungs. In case of high dose, the victim feels metallic taste in mouth, chest pain, and abdominal pain. When ingested, it gets dissolved in the
gastric acidand gets absorbed, leading to lead poisoning. High concentrations can be absorbed through skin as well; therefore it is important to keep the safety precautions when working with lead-based paint.
Long-term contact with lead tetroxide may lead to accumulation of lead compounds in organism, with development of symptoms of acute lead poisoning. Chronic poisoning displays as agitation, irritability, vision disorders,
hypertension, and usually also by grayish hue of face.
Lead tetroxide was shown to be
carcinogenicfor laboratory animals. Its carcinogenicity for humans was not proven.
Lead tetroxide was used as a red pigment in
ancient Rome, where it was prepared by calcinationof lead white. In the ancient and medieval periods it was used as a pigment in the production of illuminated manuscripts, and gave its name to the "minium" or miniature, a style of picture painted with the colour. As a finely divided powder, it was also sprinkled on dielectricsurfaces to study Lichtenberg figures. It was first isolated as a pure compound by Arabic chemists and was clearly described by Muhammad ibn Zakarīya Rāzi(Rhazes) in the early 10th century.cite web |url= http://www.history-science-technology.com/Articles/articles%2010.htm |title= Arabic Alchemy: Science of the Art |accessdate=2008-03-29 |last=Hassan |first=Ahmad Y |authorlink=Ahmad Y Hassan |work=History of Science and Technology in Islam]
* [http://www.npi.gov.au/database/substance-info/profiles/50.html National Pollutant Inventory - Lead and Lead Compounds Fact Sheet]
* [http://webmineral.com/data/Minium.shtml Minium mineral data]
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