Lead(II) sulfide
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| Lead(II) sulfide | |
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other names
Plumbous sulfide
Galena |
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| Identifiers | |
| CAS number | 1314-87-0  |
| Properties | |
| Molecular formula | PbS |
| Molar mass | 239.30 g/mol |
| Density | 7.60 g/cm3 [1] |
| Melting point |
1118 °C |
| Boiling point |
1281 °C |
| Solubility in water | 2.6 x 10-11 kg/kg (calculated, at pH=7)[2] 8.6 x 10-7 kg/kg[3] |
| Solubility product, Ksp | 9.04 x 10-29 |
| Refractive index (nD) | 3.91 |
| Structure | |
| Crystal structure | Halite (cubic), cF8 |
| Space group | Fm3m, No. 225 |
| Coordination geometry |
Octahedral (Pb2+) Octahedral (S2−) |
| Hazards | |
| MSDS | External MSDS |
| EU Index | 082-001-00-6 |
| EU classification | Repr. Cat. 1/3 Harmful (Xn) Dangerous for the environment (N) |
| R-phrases | R61, R20/22, R33, R62, R50/53 |
| S-phrases | S53, S45, S60, S61 |
| Flash point | Non-flammable |
| Related compounds | |
| Other anions | Lead(II) oxide Lead selenide Lead telluride |
| Other cations | Carbon monosulfide Silicon monosulfide Germanium(II) sulfide Tin(II) sulfide |
| Related compounds | Thallium sulfide Lead(IV) sulfide Bismuth sulfide |
| (what is this?) (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Lead(II) sulfide (also spelled sulphide) is an inorganic compound with the formula PbS. It finds limited use in electronic devices. PbS, also known as galena is the principal ore and most important compound of lead.
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Addition of hydrogen sulfide or sulfide salts to a solution of lead ions gives a poorly soluble black product consisting of PbS:
- Pb2+ + H2S → PbS + 2 H+
The equilibrium constant for this reaction is 3 x 106 M.[4] This reaction, which entails a dramatic color change from colourless or white to black, was once used in qualitative inorganic analysis. The presence of hydrogen sulfide or sulfide ions is still routinely tested using "lead acetate paper."
Like the related materials PbSe and PbTe, PbS Is semiconductor.[5] Lead sulfide crystalizes in the sodium chloride motif, unlike many other IV-VI semiconductors.
Since PbS is the main ore of lead, much effort has focused on its conversion. A major process involves smelting of PbS followed by reduction of the resulting oxide. Idealized equations for these two steps are:[6]
- PbS + 3/2 O2 → PbO + SO2
- PbO + C → Pb + CO
The sulfur dioxide is converted to sulfuric acid.
[edit] Applications
PbS was once used as a black pigment, but current applications exploit its semiconductor properties, which have long been recognized.[7] PbS is one of the oldest and most common detection element materials in various infrared detectors. As an infrared detector, PbS functions as a photon detector, responding directly to the photons of radiation, as opposed to the other main category of IR detectors, so-called thermal detectors which respond to the change of detector element temperature tcaused by the radiation.
A PbS element can be used to measure radiation in either of two ways: by measuring the tiny photocurrent the photons cause when they hit the PbS material, or by measuring the change in the material's electrical resistance that the photons cause. Measuring the resistance change is the more commonly used method.
At room temperature, PbS are sensitive to radiation at wavelengths between approximately 1 and 2.5 μm. This range corresponds to the shorter wavelengths in the infra-red portion of the spectrum, the so-called near-IR. Only very hot objects emit radiation in these wavelengths.
Cooling the PbS elements, for example using pressurised or liquified gas or a Peltier element system shifts its sensitivity range to between approximately 2 and 4 μm. Objects that emit radiation in these wavelengths still have to be quite hot - several hundred degrees Celsius - but not as hot as those which are detectable by uncooled sensors. Other compounds used for this purpose include indium antimonide (InSb) and mercury-cadmium telluride (HgCdTe), which have somewhat better properties for detecting the longer IR wavelengths. The high dielectric constant of PbS leads to relatively slow detectors (compared to silicon, germanium, InSb, or HgCdTe).
[edit] Astronomy
Elevations above 2.6 km (1.63 mi) on the planet Venus are coated with a shiny substance. Though the composition of this coat is not entirely certain, one theory is that Venus "snows" crystallized lead sulfide much as Earth snows frozen water. If this is the case, it would be the first time the substance was identified on a foreign planet. Other less likely candidates for Venus' "snow" are bismuth sulfide and tellurium.[8]
[edit] Safety
Lead(II) sulfide is toxic if the lead and sulfur are heated to decomposition and toxic compounds of lead and sulfur oxides are produced (such as in a fire).[9] Lead sulfide is insoluble and a stable compound in the PH of blood and so is probably one of the less toxic forms of lead.[10]
[edit] References
- ^ Patnaik, Pradyot (2003). Handbook of Inorganic Chemical Compounds. McGraw-Hill. ISBN 0070494398. http://books.google.com/books?id=Xqj-TTzkvTEC&pg=PA119. Retrieved 2009-06-06.
- ^ W. Linke (1965). Solubilities. Inorganic and Metal-Organic Compounds. 2. Washington, D.C.: American Chemical Society. p. 1318.
- ^ Ronald Eisler (2000). Handbook of Chemical Risk Assessment. CRC Press. ISBN 1566705061. http://books.google.ca/books?id=cl1Kry_k6ZUC&pg=PA206.
- ^ David R. Lide. CRC Handbook of Chemistry and Physics, 89th Edition (Internet Version 2009). Boca Raton, FL: CRC Press/Taylor and Francis.
- ^ Vaughan, D. J.; Craig, J. R. (1978). Mineral Chemistry of Metal Sulfides. Cambridge: Cambridge University Press. ISBN 0521214890..
- ^ Charles A. Sutherland, Edward F. Milner, Robert C. Kerby, Herbert Teindl, Albert Melin, Hermann M. Bolt (2005). Lead. in Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:.
- ^ Putley, E H (1951). "Lead Sulphide - An Intrinsic Semiconductor". Proceedings of the Physical Society Section B 64: 616. doi:.
- ^ "'Heavy metal' snow on Venus is lead sulfide". Washington University in St. Louis. http://news-info.wustl.edu/news/page/normal/633.html. Retrieved 2009-07-07.
- ^ MSDS http://www.espimetals.com/msds%27s/leadsulfide.pdf
- ^ Studies on the Toxicity of Various Lead Compounds Given Intravenously. Fritz Bischoff, L. C. Maxwell, Richard D. Evens and Franklin R. Nuzum. Journal of Pharmacology and Experimental Therapeutics, September 1928 vol. 34 no. 1 85-109 http://jpet.aspetjournals.org/content/34/1/85.abstract
