Lead(II,IV) oxide, also called red lead or minium, is the inorganic compound with the formula . A bright red or orange solid, it is used as pigment, in the manufacture of batteries, and rustproof primer paints. It is an example of a mixed valence compound, being composed of both Pb(II) and Pb(IV) in the ratio of two to one.

Structure

Lead(II,IV) oxide is lead(II) orthoplumbate(IV) . It has a tetragonal crystal structure at room temperature, which then transforms to an orthorhombic ( Pearson symbol ''oP''28, Space group Pbam, No. 55) form at temperature . This phase transition only changes the symmetry of the crystal and slightly modifies the interatomic distances and angles. File:Red-lead-unit-cell-3D-balls.png, Unit cell of tetragonal
(Key: Pb O) File:Red-lead-3D-balls.png, Part of tetragonal red lead's crystal structure

Preparation

Lead(II,IV) oxide is prepared by calcination of lead(II) oxide (PbO; also called litharge) in air at about 450–480 °C: : The resulting material is contaminated with PbO. If a pure compound is desired, PbO can be removed by a

potassium hydroxide Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash. Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which utili ...

solution: : Another method of preparation relies on annealing of lead(II) carbonate ( cerussite) in air: : Yet another method is oxidative annealing of white lead: : In solution, lead(II,IV) oxide can be prepared by reaction of potassium plumbate with lead(II) acetate, yielding yellow insoluble lead(II,IV) oxide monohydrate , which can be turned into the anhydrous form by gentle heating: : Natural minium is uncommon, forming only in extreme oxidizing conditions of

lead Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...

ore bodies. The best known natural specimens come from Broken Hill,

New South Wales New South Wales (commonly abbreviated as NSW) is a States and territories of Australia, state on the Eastern states of Australia, east coast of :Australia. It borders Queensland to the north, Victoria (state), Victoria to the south, and South ...

, Australia, where they formed as the result of a mine fire.

Reactions

Red lead is virtually insoluble in water and in

ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...

. However, it is soluble in hydrochloric acid present in the stomach, and is therefore toxic when ingested. It also dissolves in glacial acetic acid and a diluted mixture of

nitric acid Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...

and hydrogen peroxide. When heated to 500 °C, it decomposes to lead(II) oxide and oxygen. At 580 °C, the reaction is complete. :

Nitric acid Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...

dissolves the lead(II) oxide component, leaving behind the insoluble lead(IV) oxide: : With iron oxides and with elemental

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

, lead(II,IV) oxide forms insoluble iron(II) and iron(III) plumbates, which is the basis of the anticorrosive properties of lead-based paints applied to iron objects.

Use

Red lead has been used as a

pigment A pigment is a powder used to add or alter color or change visual appearance. Pigments are completely or nearly solubility, insoluble and reactivity (chemistry), chemically unreactive in water or another medium; in contrast, dyes are colored sub ...

for primer paints for

objects. Due to its

toxicity Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacteria, bacterium, or plant, as well as the effect o ...

, its use is being limited. It finds limited use in some amateur pyrotechnics as a delay charge and was used in the past in the manufacture of dragon's egg pyrotechnic stars. Red lead is used as a curing agent in some polychloroprene rubber compounds. It is used in place of magnesium oxide to provide better water resistance properties. Red lead was used for engineer's scraping, before being supplanted by engineer's blue. Although red lead still offers more accurate markings since it doesn't flow as readily as engineer's blue under pressure. It is also used as an adulterating agent in turmeric powder.

Physiological effects

When inhaled, lead(II,IV) oxide irritates the lungs. In case of high dose, the victim experiences a metallic taste, chest pain, and abdominal pain. When ingested, it is dissolved in the gastric acid and absorbed, leading to

lead poisoning Lead poisoning, also known as plumbism and saturnism, is a type of metal poisoning caused by lead in the body. Symptoms may include abdominal pain, constipation, headaches, irritability, memory problems, infertility, numbness and paresthesia, t ...

. High concentrations can be absorbed through skin as well, and it is important to follow safety precautions when working with lead-based paint. Long-term contact with lead(II,IV) oxide may lead to accumulation of lead compounds in organisms, with development of symptoms of acute lead poisoning. Chronic poisoning displays as agitation, irritability, vision disorders,

hypertension Hypertension, also known as high blood pressure, is a Chronic condition, long-term Disease, medical condition in which the blood pressure in the artery, arteries is persistently elevated. High blood pressure usually does not cause symptoms i ...

, and a grayish facial hue. Lead(II,IV) oxide was shown to be

carcinogenic A carcinogen () is any agent that promotes the development of cancer. Carcinogens can include synthetic chemicals, naturally occurring substances, physical agents such as ionizing and non-ionizing radiation, and Biological agent, biologic agent ...

for laboratory animals. Its carcinogenicity for humans was not proven. Minium- BYU

History

This compound's

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

name ''minium'' originates from the Minius, a river in northwest Iberia where it was first mined. Lead(II,IV) oxide was used as a red pigment in

ancient Rome In modern historiography, ancient Rome is the Roman people, Roman civilisation from the founding of Rome, founding of the Italian city of Rome in the 8th century BC to the Fall of the Western Roman Empire, collapse of the Western Roman Em ...

, where it was prepared by calcination of white lead. In the ancient and medieval periods it was used as a pigment in the production of

illuminated manuscript An illuminated manuscript is a formally prepared manuscript, document where the text is decorated with flourishes such as marginalia, borders and Miniature (illuminated manuscript), miniature illustrations. Often used in the Roman Catholic Churc ...

s, and gave its name to the ''minium'' or miniature, a style of picture painted with the colour. Made into a paint with

linseed oil Linseed oil, also known as flaxseed oil or flax oil (in its edible form), is a colorless to yellowish oil obtained from the dried, ripened seeds of the flax plant (''Linum usitatissimum''). The oil is obtained by pressing, sometimes followed by ...

, red lead was used as a durable paint to protect exterior ironwork. In 1504 the portcullis at Stirling Castle in Scotland was painted with red lead, as were cannons including Mons Meg. As a finely divided powder, it was also sprinkled on dielectric surfaces to study Lichtenberg figures. In traditional Chinese medicine, red lead is used to treat ringworms and ulcerations, though the practice is limited due to its toxicity. Also, ''azarcón'', a Mexican folk remedy for gastrointestinal disorders, contains up to 95% lead(II,IV) oxide. It was also used before the 18th century as medicine.

References

External links

National Pollutant Inventory - Lead and Lead Compounds Fact SheetMinium mineral data
{{Oxides Corrosion inhibitors Inorganic pigments Mixed valence compounds Oxides Pyrotechnic oxidizers