He Lead oxide , Also known as lead oxide (II) or lead monoxide, is a chemical compound of the formula PbO.
Lead oxide (II) is found in two polymorphs: Lizard and the Masicotite . The structure of the plumbous oxide is illustrated in Figure 1.
Figure 1: plumbous oxide structure.
Turning to the composition, litharge is the oxidized product of molten lead that has been agitated or atomized to incorporate air, then cooled and ground to form the yellow powder.
The name masicotite is used for both the native mineral and the lead monoxide product produced by heating lead carbonate at 300 ° C (Lead Monoxide, 2016). These minerals are shown in Figure 2.
Figure 2: polymorphs of masicotita (left) and litargirio (right)
The masicotite has an orthorhombic structure while the litharge has a tetragonal crystalline structure. Lead oxide (II) has the ability to change structure upon heating or cooling. These structures are shown in Figure 3.
Figure 3: Orthorhombic crystalline structure of the masicotite (left) and tetragonal of the litargirio (der.).
PbO is produced by oxidizing metallic lead. The metal is melted to make lead tablets, and then grinded at 170 ~ 210 ° C and passed through the flame for oxidation at temperatures above 600 ℃. The oxide products are ground to obtain the finished lead oxide (Kirk-Othmer, 1995).
2Pb + O2 → 2PbO
PbO is produced on a large scale as an intermediate product in the refining of lead minerals into metallic lead. The lead ore used is galena (lead sulfide (II)). At high temperature (1000 ° C) the sulfide is converted to the oxide as follows:
2PbS + 3O2 → 2PbO + 2SO2
Physical and chemical properties of lead oxide
Lead monoxide can have two different appearances: as yellow dry powder with orthorhombic structure (masicotite) or as tetragonal crystals of reddish color (litargirio). Both forms are illustrated in Figure 4.
Figure 4: PbO appearance: masicotita (left) and litargirio (right).
The compound has a molecular weight of 223.20 g / mol and a density of 9.53 g / ml. It has a melting point of 888 ° C and a boiling point of 1470 ° C (National Center for Biotechnology Information, S.F.).
The compound is very sparingly soluble in water, and only 0.0504 grams per liter at 25 ° C in the form of masicotite and 0.1065 grams per liter at 25 ° C in the form of litharge can be dissolved. The compound is also insoluble in alcohol. It is soluble in acetic acid, dilute HNO3 and alkalis (Royal Society of Chemistry, 2015).
The compound is a weak oxidizing or reducing agent, however, reactions of Redox . These compounds are not reactive to water.
Lead oxide oxidizes to aluminum carbide with incandescence on heating. Mixtures of lead oxide with aluminum powder (as with other metals: sodium, zirconium) give a violent explosion.
Reactivity and hazards
Lead monoxide is a compound classified as poisonous. The substance is toxic to the central nervous system and may be carcinogenic to humans (Material Safety Data Sheet Lead oxide, yellow, 2013).
The symptom of early poisoning are lead lines that appear at the edge of the gums and the skin turns gray. The neurasthenic syndrome will also arise in the initial period of poisoning.
Cerebellar poisoning can result in depression due to lead poisoning, lead poisoning mania, as well as lead toxicity and multiple neuritis palsy sensitivity.
Lead poisoning can also cause hypochromic anemia and metabolic and endocrine disorders. In addition, lead poisoning can inhibit the activity of certain enzymes in the digestive system and cause indigestion, severe abdominal pain and liver damage. It can also cause high blood pressure and increased cholesterol.
If there is severe abdominal pain, some measures can be taken such as, subcutaneous injection of atropine and other drugs, warm abdominal, enema, hot water bath and so on. The maximum permissible air concentration is 0.01 mg / m3 (Lead monoxide, 2016).
In case of contact with eyes or skin, wash with plenty of water. In case of inhalation or ingestion, the victim should be taken to a ventilated place. Do not induce vomiting. If the victim is not breathing, mouth-to-mouth resuscitation should be given.
In all cases seek immediate medical attention. Lead monoxide is a compound harmful to the environment, bioaccumulation of this chemical can occur in plants and mammals.
It is strongly recommended that this substance does not enter the environment, so it must be handled and stored according to the established provisions (National Institute for Occupational Safety and Health, 2015).
Applications
Lead monoxide has been used as a paint dryer and as a low fire flux in the manufacture of ceramics and glass. Lead glass is used in the manufacture of high quality tableware.
Using lead monoxide as a flux, it is possible to obtain a glass with a high refractive index and therefore, the desired brightness (British Encyclopedia, 2016).
Semi-metallic ceramic conductors have the highest conductivities of all ceramics except superconductors. Lead oxide is an example of this type of semimetallic ceramics. These materials have superimposed electron energy bands and are therefore excellent electronic conductors (Mason, 2008).
Lead oxide is mainly used in electron tubes, imaging tubes, optical glass, anti-X-ray lead glass and radiation-resistant rubbers.
It is used as analytical reagent, the flow of silicate, but also for the precipitation of amino acids
Lead oxide is used in the manufacture of plastic PVC stabilizer and is also the raw material of other lead salts. It is also used in petroleum refining and for the determination of gold and silver.
It is also used as a yellow pigment in paints and enamels. The masicotite was used as a pigment of artists from the 15th to the 18th centuries. Thin layers of lead monoxide are used to produce iridescent brass and bronze colors. The litharge is mixed with glycerol to make the cement of the plumber.
References
- British Encyclopedia. (2016, October 10). Glass. Recovered from britannica: britannica.com.
- Kirk-Othmer. (nineteen ninety five). Encyclopedia of Chemical Technology. 4th ed. Volumes 1. New York: John Wiley and Sons.
- Lead monoxide. (2016, May 1). Recovered from cameo.mfa: cameo.mfa.org.
- Lead monoxide. (2016). Recovered from chemicalbook: chemicalbook.com.
- Mason, T. O. (2008, March 12). Conductive ceramics. Recovered from britannica: britannica.com.
- Material Safety Data Sheet Lead oxide, yellow. (2013, May 21). Recovered from sciencelab: sciencelab.com.
- National Center for Biotechnology Information. (S.F.). PubChem Compound Database; CID = 14827. Recovered from PubChem: pubchem.ncbi.nlm.nih.gov.
- National Institute for Occupational Safety and Health. (2015, July 22). LEAD (II) OXIDE. Retrieved from cdc.gov: cdc.gov.
- Royal Society of Chemistry. (2015). Lead (II) oxide. Recovered from chemspider: chemspider.com.