Cadmium sulfide

Chembox new
Name = Cadmium sulfide
ImageFile = Hawleyite-3D-balls.png ImageSize = 150px
ImageName = 3D model of the structure of hawleyite
ImageFile1 = Greenockite-3D-balls.png ImageSize1 = 150px
ImageName1 = 3D model of the structure of greenockite
OtherNames = Cadmium(II) sulfide
Section1 = Chembox Identifiers
CASNo = 1306-23-6
EINECS = 215-147-8
RTECS = EV3150000
Section2 = Chembox Properties
Formula = CdS
MolarMass = 144.46 g/mol
Appearance = Yellow-orange solid.
Density = 4.82 g/cm³, solid.
Solubility = Insoluble
MeltingPt = 1750°C at 100 bar
BoilingPt = 980°C "subl."
Section3 = Chembox Structure
Coordination =
CrystalStruct = Hexagonal
Section7 = Chembox Hazards
EUClass = Toxic
Carc. Cat. 2
Muta. Cat. 3
Repr. Cat. 3
Dangerous for
the environment
FlashPt = non flammable
Section8 = Chembox Other
OtherAnions = Cadmium oxide
Cadmium selenide
OtherCations = Zinc sulfide
Mercury sulfide

Cadmium sulfide is a chemical compound with the formula CdS. Cadmium sulfide is yellow in colour and is a semiconductor.Egon Wiberg, Arnold Frederick Holleman (2001) "Inorganic Chemistry", Elsevier ISBN 0123526515] It exists in nature as two different minerals, greenockite and hawleyite. [Hawleyite, isometric cadmium sulphide, a new mineral Traill R J, Boyle R W American Mineralogist 40 (1955) 555-559 ] Cadmium sulfide is a direct band gap semiconductor (gap 2.42 eVCharles Kittel Introduction to Solid State Physics- 7th Edition (1995) Wiley-India ISBN 1081-265-1045-5] ) and has many applications for example in light detectors. It forms thermally stable pigments and with the addition of e.g CdTe, HgS colours ranging from deep red to yellow are formed.Greenwood&Earnshaw]

Preparation

Cadmium sulfide can be prepared by the precipitation from soluble cadmium(II) salts with sulfide ion and this has been used in the past for the gravimetric analysis of cadmium. [Fred Ibbotson (2007) The Chemical Analysis of Steel-Works' MaterialsREAD BOOKS ISBN 1406781134]
Pigment production usually involves the precipitation of CdS, the washing of the precipitate to remove soluble cadmium salts followed by calcination(roasting) to convert it to the hexagonal form followed by milling to produce a powder. Hugh MacDonald Smith High Performance Pigments 2002 Wiley-VCH ISBN 3527302042 ] When cadmium sulfide selenides are required the CdSe is co-precipitated with CdS and the cadmium sulfoselenide is created during the calcination step.
Industrially the production of thin films of CdS is required in e.g. photoresistors and CBD, Chemical bath deposition, has been investigated using the hydrolysis of thiourea as the source of sulfide anions and an ammonium salt /ammonia buffer solution to control pH:Optimization of Chemical Bath Deposited Cadmium Sulfide, I.O. Oladeji, L. Chow, J. Electrochem. Soc., 144, 7, (1997)] :Cd²⁺ + NH₃ → [Cd(NH₃)₄] ²⁺

:NH₂CS + OH⁻ → SH⁻ + H₂O + H₂CN₂

:SH⁻ + OH⁻ → S²⁻ + CdS

Cadmium sulfide can be produced from volatile cadmium alkyls, an example is the reaction of dimethylcadmium with diethyl sulfide to produce a film of CdS using MOCVD techniques.Thin CdS films prepared by metalorganic chemical vapor deposition, Hiroshi Uda, Hideo Yonezawa, Yoshikazu Ohtsubo, Manabu Kosaka and Hajimu Sonomura Solar Energy Materials and Solar Cells 75, 1-2, (2003), 219-226 doi|10.1016/S0927-0248(02)00163-0 ]

The preparative route and the subsequent treatment of the product, affects the polymorphic form that is produced. It has been asserted in the past that chemical precipitation methods produce the cubic zincblende form [Paul Klocek (1991) Handbook of Infrared Optical Materials CRC Press ISBN 0824784685] however there more recent examples where the hexagonal form is produced, e.g. see [Optical characterization of vacuum evaporated cadmium sulfide films U. Pal, R. Silva-González, G. Martínez-Montes, M. Gracia-Jiménez, M.A. Vidal and Sh. Torres Thin Solid Films 305, 1-2, 1997, 345-350,doi|10.1016/S0040-6090(97)00124-7]

Chemical Properties

Cadmium sulfide is soluble in acids and this has been investigated as a method of extracting the pigment from waste polymers e.g. HDPE pipes: [Extraction of CdS pigment from waste polyethylene Wanrooij P. H. P., Agarwal U. S., Meuldijk J., van Kasteren J. M. N., Lemstra P. J., Journal of Applied Polymer Science 100, 2 , 1024 – 1031 doi|10.1002/app.22962] :CdS + HCl → CdCl₂ + H₂S

When sulfide solutions containing dispersed CdS particles are irradiated with light hydrogen gas is generated:Mario Schiavello (1985 ) Photoelectrochemistry, Photocatalysis, and Photoreactors: Fundamentals and Developments Springer ISBN 9027719462] : H₂S → H₂ + S ΔH_f = +9.4 kcal/molThe reaction mechanism proposed involves the electron/hole pairs created when incident light is absorbed by the cadmium sulfide followed by these reacting with water and sulfide::Production of an electron hole pair::CdS + "h"ν → e⁻ + hole⁺ :Reaction of electron::2e⁻ + 2H₂O → H₂ + 2OH⁻:Reaction of hole::2hole⁺ + S²⁻ → S

tructure and Physical Properties

Cadmium sulfide has, like zinc sulfide, two crystal forms; the more stable hexagonal wurtzite structure (found in the mineral Greenockite) and the cubic zinc blende structure (found in the mineral Hawleyite). In both of these forms the Cadmium and sulfur atoms are four coordinate. Wells A.F. (1984) "Structural Inorganic Chemistry" 5th edition Oxford Science Publications ISBN 0-19-855370-6 ] There is also a high pressure form with the NaCl rock salt structure.

Cadmium sulfide is a direct bandgap semiconductor with a bandgap of 2.42 eV at 300 K.The magnitude of its band gap means that it appears coloured.
As well as this obvious property others properties result:

*the conductivity increases when irradiated with light(leading to uses as a photoresistor)
*when combined with a p-type semiconductor it forms the core component of a photovoltaic (solar) cell and a CdS/Cu₂S solar cell was one of the first efficient cells to be reported (1954) [Antonio Luque, Steven Hegedus, (2003), Handbook of Photovoltaic Science and Engineering John Wiley and Sons ISBN 0471491969] [Photovoltaic Effect in Cadmium Sulfide D. C. Reynolds, G. Leies, L. L. Antes, R. E. Marburger, Phys. Rev. 96, 2, 533 - 534 (1954) doi|10.1103/PhysRev.96.533]
*when doped with for example Cu⁺ ("activator")and Al³⁺ ("coactivator") CdS luminesces under electron beam excitation (cathodoluminescence) and is used as phosphor [C. Fouassier,(1994), "Luminescence" in Encyclopedia of Inorganic Chemistry, John Wiley & Sons ISBN 0471936200]
*both polymorphs are piezoelectric and the hexagonal is also pyroelectricA. K. Cheetham, P. Day 1992 Solid State Chemistry: Compounds Oxford University Press ISBN 0198551665 ] [Temperature Dependence of the Pyroelectric Effect in Cadmium Sulfide W. J. Minkus Phys. Rev. 138, A1277 - A1287 (1965) doi|10.1103/PhysRev.138.A1277]
*electroluminescence [Low-Field Electroluminescence in Insulating Crystals of Cadmium Sulfide, Roland W. Smith, Phys. Rev. 105, 900 - 904 (1957) doi|10.1103/PhysRev.105.900]
*solid CdS can act as a solid state laser [KGP-2: an electron-beam-pumped cadmium sulfide laser, Yu A Akimov, A A Burov, Yu A Drozhbin, V A Kovalenko, S E Kozlov, I V Kryukova, G V Rodichenko, B M Stepanov, V A Yakovlev, Sov. J. Quantum Electron. 2 284-285 doi|10.1070/QE1972v002n03ABEH004443] [Lasing in single cadmium sulfide nanowire optical cavities, Agarwal R, Barrelet CJ, Lieber CM.,Nano Lett. 2005 5(5):917-20. [http://arXiv:cond-mat/0412144v1] ]

Industrial Processes used to produce thin films

Thin films of CdS are required in components such as a photoresistor and solar cells. Various methods have been used to deposit these thin films, for example (note: there is a large body of research in this area and only representative references are given):
*Chemical bath deposition, CBD
*Sol gel techniques [ Nanosized semiconductor particles in glasses prepared by the sol–gel method: their optical properties and potential uses, Journal of Alloys and Compounds, 341, 1-2,(2002),56-61,doi|10.1016/S0925-8388(02)00059-2]
*MOCVD
*Sputtering [Comparative studies of the properties of CdS films deposited on different substrates by R.F. sputtering, Byung-Sik Moon, Jae-Hyeong Lee, Hakkee Jung, Thin Solid Films,511-512,(2006),299-303,doi|10.1016/j.tsf.2005.11.080 ]
*Electrochemical deposition [Defect reduction in electrochemically deposited CdS thin films by annealing in 0₂ Fumitaka Goto, Katsunori Shirai, Masaya Ichimura, Solar Energy Materials and Solar Cells, 50, 1-4, (1998), 147-153, doi|10.1016/S0927-0248(97)00136-0]
*Spraying with precursor cadmium salt, sulfur compound and dopant [United States Patent 4,086,101, Photovoltaic cells, J.F. Jordan, C.M. Lampkin Issue date: April 25, 1978]
*Screen printing using a slurry containing dispersed CdS [US Patent 3208022, High performance photoresistor,Y . T. Sihvonen Issue date: September 21, 1965]

Pigment

CdS is known as Cadmium yellow (CI pigment yellow 37Colour Chemistry R. M. Christie 2001 Royal Society of Chemistry ISBN 0854045732] ) By adding varying amounts of selenium as selenide it is possible to obtain a range of colors for example CI pigment orange 20 and CI pigment red 108.
Synthetic cadmium pigments based on cadmium sulfide are valued for their good thermal stability, light and weather fastness, chemical resistance and high opacity.The general commercial availability of cadmium sulfide from the 1840s lead to its adoption by artists notably
Van Gogh, Monet(in his London series and other works) and Matisse ("Bathers by a river" 1916-1919) [Sidney Perkowitz 1998 Empire of Light: A History of Discovery in Science and Art, Joseph Henry Press, ISBN 0309065569 ] the presence of cadmium in paints has been used to detect forgeries in paintings alleged to have been produced prior to the 19th century. [W. Stanley Taft, James W. Mayer, Richard Newman, Peter Kuniholm, Dusan Stulik (2000) The Science of Paintings, Springer, ISBN 0387987223] CdS is used as pigment in plastics

Biological

Cadmium sulfide is produced by sulfate reducing bacteria. [Larry L. Barton 1995 Sulfate reducing bacteria, Springer, ISBN 0306448572] This ability is being investigated as a means of producing nano- crystalline CdS [Bacterial Biosynthesis of Cadmium Sulfide Nanocrystals. R. Sweeney, C. Mao, X. Gao, J. Burt, A. Belcher, G. Georgiou, B. Iverson, Chemistry & Biology, 11 , 11 , 1553 - 1559, doi|10.1016/j.chembiol.2004.08.022 ]

References

* [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc04/icsc0404.htm International Chemical Safety Card 0404]
* [http://www.webelements.com/webelements/compounds/text/Cd/Cd1S1-1306236.html Cadmium(II) sulphide information at Webelements]

External links

* [http://www-cie.iarc.fr/htdocs/monographs/vol58/mono58-2.htm IARC Monograph: "Cadmium and Cadmium Compounds"] Last access November 2005.
* [http://www.npi.gov.au/database/substance-info/profiles/17.html National Pollutant Inventory - Cadmium and compounds]
* [http://www.mod.uk/DefenceInternet/AboutDefence/CorporatePublications/ScienceandTechnologyPublications/InformationSheets/ZincCadmiumSulphideDispersionTrials.htm] Report by the Academy of Medical Sciences to the Chief Scientific Adviser, Ministry of Defence on the Zinc Cadmium Sulphide dispersion trials undertaken in the United Kingdom between 1953 and 1964.