Chemical compound

Lead(II) oxide, also called lead monoxide, is the inorganic compound with the molecular formula PbO. PbO occurs in two polymorphs: litharge having a tetragonal crystal structure, and massicot having an orthorhombic crystal structure. Modern applications for PbO are mostly in lead-based industrial glass and industrial ceramics, including computer components. It is an amphoteric oxide.[3]

Preparation

PbO may be prepared by heating lead metal in air at approximately 600 °C (1,100 °F). At this temperature it is also the end product of oxidation of other oxides of lead in air:[4]

Thermal decomposition of lead(II) nitrate or lead(II) carbonate also results in the formation of PbO:

Pb(NO
3
)
2
→ 2 PbO + 4 NO
2
+ O
2
PbCO
3
→ PbO + CO2

PbO is produced on a large scale as an intermediate product in refining raw lead ores into metallic lead. The usual lead ore is galena (lead(II) sulfide). At a temperature of around 1,000 °C (1,800 °F) the sulfide is converted to the oxide:[5]

2 PbS + 3 O
2
→ 2 PbO + 2 SO2

Metallic lead is obtained by reducing PbO with carbon monoxide at around 1,200 °C (2,200 °F):[6]

PbO + CO → Pb + CO2

Structure

As determined by X-ray crystallography, both polymorphs, tetragonal and orthorhombic feature a pyramidal four-coordinate lead center. In the tetragonal form the four lead–oxygen bonds have the same length, but in the orthorhombic two are shorter and two longer. The pyramidal nature indicates the presence of a stereochemically active lone pair of electrons.[7] When PbO occurs in tetragonal lattice structure it is called litharge; and when the PbO has orthorhombic lattice structure it is called massicot. The PbO can be changed from massicot to litharge or vice versa by controlled heating and cooling.[8] The tetragonal form is usually red or orange color, while the orthorhombic is usually yellow or orange, but the color is not a very reliable indicator of the structure.[9] The tetragonal and orthorhombic forms of PbO occur naturally as rare minerals.

Crystal structure of the litharge form of lead(II) oxide[4][10][11]
Unit cell Packing Packing Packing Lead coordination Oxygen coordination
PbO-litharge-xtal-unit-cell-3D-bs-17.png PbO-litharge-xtal-3x3x3-3D-bs-17.png PbO-litharge-xtal-3x3x3-a-3D-bs-17.png PbO-litharge-xtal-3x3x3-c-3D-bs-17.png PbO-litharge-xtal-Pb-coordination-3D-bs-17.png PbO-litharge-xtal-O-coordination-3D-bs-17.png
3×3×3 unit cells viewed along the a axis viewed along the c axis square pyramidal distorted tetrahedral

Reactions

The red and yellow forms of this material are related by a small change in enthalpy:

PbO(red) → PbO(yellow)   ΔH = 1.6 kJ/mol

PbO is amphoteric, which means that it reacts with both acids and with bases. With acids, it forms salts of Pb2+
via the intermediacy of oxo clusters such as [Pb
6
O(OH)
6
]4+
. With strong bases, PbO dissolves to form plumbite (also called plumbate(II)) salts:[12]

PbO + H2O + OH
[Pb(OH)
3
]

Applications

The kind of lead in lead glass is normally PbO, and PbO is used extensively in making glass. Depending on the glass, the benefit of using PbO in glass can be one or more of increasing the refractive index of the glass, decreasing the viscosity of the glass, increasing the electrical resistivity of the glass, and increasing the ability of the glass to absorb X-rays. Adding PbO to industrial ceramics (as well as glass) makes the materials more magnetically and electrically inert (by raising their Curie temperature) and it is often used for this purpose.[13] Historically PbO was also used extensively in ceramic glazes for household ceramics, and it is still used, but not extensively any more. Other less dominant applications include the vulcanization of rubber and the production of certain pigments and paints.[3] PbO is used in cathode ray tube glass to block X-ray emission, but mainly in the neck and funnel because it can cause discoloration when used in the faceplate. Strontium oxide and Barium oxide are preferred for the faceplate.[14]

The consumption of lead, and hence the processing of PbO, correlates with the number of automobiles, because it remains the key component of automotive lead–acid batteries.[15]

Niche or declining uses

A mixture of PbO with glycerine sets to a hard, waterproof cement that has been used to join the flat glass sides and bottoms of aquariums, and was also once used to seal glass panels in window frames. It is a component of lead paints.

PbO was used to speed up the process to turn more profit for less time and artificially increase the quality of century eggs, a type of Chinese preserved egg. It was an unscrupulous practice in some small factories but it became rampant in China and forced many honest manufacturers to label their boxes "lead-free" after the scandal went mainstream in 2013.

In powdered tetragonal litharge form, it can be mixed with linseed oil and then boiled to create a weather-resistant sizing used in gilding. The litharge would give the sizing a dark red color that made the gold leaf appear warm and lustrous, while the linseed oil would impart adhesion and a flat durable binding surface.

PbO is used in certain condensation reactions in organic synthesis.[16]

PbO is the input photoconductor in a video camera tube called the Plumbicon.

Health issues

PbOlabel.jpg

Lead oxide may be fatal if swallowed or inhaled. It causes irritation to skin, eyes, and respiratory tract. It affects gum tissue, the central nervous system, the kidneys, the blood, and the reproductive system. It can bioaccumulate in plants and in mammals.[17]

References

  1. ^ Blei(II)-oxid. Merck
  2. ^ "Lead compounds (as Pb)". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  3. ^ a b Carr, Dodd S. (2005). "Lead Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a15_249.
  4. ^ a b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. pp. 382–387. ISBN 978-0-08-037941-8.
  5. ^ Abdel-Rehim, A. M. (2006). "Thermal and XRD analysis of Egyptian galena". Journal of Thermal Analysis and Calorimetry. 86 (2): 393–401. doi:10.1007/s10973-005-6785-6. S2CID 96393940.
  6. ^ Lead Processing @ Universalium.academic.ru. Alt address: Lead processing @ Enwiki.net.
  7. ^ Wells, A. F. (1984), Structural Inorganic Chemistry (5th ed.), Oxford: Clarendon Press, ISBN 0-19-855370-6[page needed]
  8. ^ A simple example is given in Anil Kumar De (2007). "§9.2.6 Lead (Pb): Lead Monoxide PbO". A Textbook Of Inorganic Chemistry. New Age International. p. 383. ISBN 978-81-224-1384-7. A more complex example is in Turova, N.Y. (2002). "§9.4 Germanium, tin, lead alkoxides". The Chemistry of Metal Alkoxides. Springer. p. 115. ISBN 978-0-7923-7521-0.
  9. ^ Rowe, David John (1983). Lead Manufacturing in Britain: A History. Croom Helm. p. 16. ISBN 978-0-7099-2250-6.
  10. ^ Pirovano, Caroline; Islam, M. Saiful; Vannier, Rose-Noëlle; Nowogrocki, Guy; Mairesse, Gaëtan (2001). "Modelling the crystal structures of Aurivillius phases". Solid State Ion. 140 (1–2): 115–123. doi:10.1016/S0167-2738(01)00699-3.
  11. ^ "ICSD Entry: 94333". Cambridge Structural Database: Access Structures. Cambridge Crystallographic Data Centre. Retrieved 2021-06-01.
  12. ^ Holleman, Arnold Frederik; Wiberg, Egon (2001), Wiberg, Nils (ed.), Inorganic Chemistry, translated by Eagleson, Mary; Brewer, William, San Diego/Berlin: Academic Press/De Gruyter, ISBN 0-12-352651-5[page needed]
  13. ^ Chapter 9, "Lead Compounds", in the book Ceramic and Glass Materials: Structure, Properties and Processing, published by Springer, year 2008.
  14. ^ Compton, Kenneth (5 December 2003). Image Performance in CRT Displays. SPIE Press. ISBN 9780819441447 – via Google Books.
  15. ^ Sutherland, Charles A.; Milner, Edward F.; Kerby, Robert C.; Teindl, Herbert; Melin, Albert; Bolt, Hermann M. "Lead". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a15_193.pub2.
  16. ^ Corson, B. B. (1936). "1,4-Diphenylbutadiene". Organic Syntheses. 16: 28.; Collective Volume, vol. 2, p. 229
  17. ^ "Lead(II) oxide". International Occupational Safety and Health Information Centre. Archived from the original on 2011-12-15. Retrieved 2009-06-06.

External links