Lead oxide has a tetragonal crystal structure at room temperature, which then transforms to an orthorhombic form at temperature. This phase transition only changes the symmetry of the crystal and slightly modifies the interatomic distances and angles.
Preparation
Lead oxide is prepared by calcination of lead oxide 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 solution: Another method of preparation relies on annealing of lead carbonate in air: Yet another method is oxidative annealing of white lead: In solution, lead oxide can be prepared by reaction of potassium plumbate with lead acetate, yielding yellow insoluble lead oxide monohydrate, Pb3O4·H2O, which can be turned into the anhydrous form by gentle heating: Natural minium is uncommon, forming only in extreme oxidizing conditions of lead ore bodies. The best known natural specimens come fromBroken Hill, New South Wales, Australia, where they formed as the result of a mine fire.
Reactions
Red lead is virtually insoluble in water and in ethanol. 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 and hydrogen peroxide. When heated to 500 °C, it decomposes to lead oxide and oxygen. At 580 °C, the reaction is complete. Nitric acid dissolves the lead oxide component, leaving behind the insoluble lead oxide: With iron oxides and with elemental iron, lead oxide forms insoluble iron and iron plumbates, which is the basis of the anticorrosive properties of lead-based paints applied to iron objects.
When inhaled, lead oxide irritates 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. 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 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, and a grayish facial hue. Lead oxide was shown to be carcinogenic for laboratory animals. Its carcinogenicity for humans was not proven. , Australia
History
This compound's Latin nameminium originates from the Minius, a river in northwest Iberia where it was first mined. Lead oxide was used as a red pigment in ancient Rome, 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 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 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 oxide. It was also used before the 18th century as medicine.
