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| Lead(II) sulfide | |
|---|---|
| Systematic name | Lead(II) sulfide |
| Other names | xxx, xxx |
| Molecular formula | PbS |
| Molar mass | 239.28 g/mol |
| Density | 7700 kg/m3 |
| Solubility (water) | x.xx g/l |
| Melting point | 1390 K |
| Boiling point | xx.x °C |
| CAS number | * |
| Dielectric constant | 200 |
| Band gap | 0.41 eV |
| Index of refraction | 3.9120 |
| Chemical infobox | |
Lead sulfide (British/Commonwealth English sulphide) is a chemical compound , most often purified from the mineral galena. PbS, PbSe and PbTe lead salts are semiconductors of the IV-VI family. Lead sulphide is toxic due to the lead content, see lead poisoning.
Applications
Lead sulfide and several other lead salts are used as detection element material in various infra-red sensors. Of these, PbS (lead sulfide) is one of the oldest and most commonly used. It is used for eg. infrared detectors.
When used as IR detection element material they are classified as photon detectors: this means that unlike thermal detectors (the other major type), they react directly to the photons of incoming light radiation hitting the material. Thermal detectors react only to the eventual temperature rise in the material caused by the energy from the photons. Because of this, radiation can then be measured in two ways: either by detecting the tiny electrical current the photons cause when they hit the PbS surface, or by measuring the change in its electrical resistance. Measuring the resistance change is the more commonly used method.
At room temperature, PbS elements are sensitive to radiation at wavelengths between approximately 1 and 2.5 μm. This corresponds to the shorter wavelengths in the IR band, and is called near-IR, a term which refers to the fact that it is close to the wavelengths of visible light. Only very hot objects emit radiation in these wavelengths.
Cooling the PbS elements, for example using pressurised or liquified gas or a Peltier system shifts its sensitivity range to between approximately 2 and 4 μm. Objects which 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 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).
PbS can be formed as nanocrystals.
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. *
See also
References
- Lead Sulphide - An Intrinsic Semiconductor, E H Putley and J B Arthur, Proc. Phys. Soc. B, 64 pp. 616-618 (1951)
- Absorption Spectra of Lead Sulphide at Different Temperatures, W. Paui and R. V. Jones, Proc. Phys. Soc. B, 6 (3) pp. 194-200 (1953).
- Electronic and Vibrational Properties of Lead Sulphide Nanocrystals, Janet Lynn Machol, Ph.D. Thesis, Cornell Univ. (1993).
- Nonlinear optical properties of lead sulfide nanocrystals in polymeric coatings, S W Lu et al, Nanotechnology 13 669-673 (2002)
External links
- Case Studies in Environmental Medicine (CSEM): Lead Toxicity
- ToxFAQs™: Lead
- National Pollutant Inventory - Lead and Lead Compounds Fact Sheet
- MSDS at Oxford university.
Lead compounds | Sulfides | Semiconductor materials | Infrared imaging
"Lead(II) sulfide"