Thallium(I) sulfide, Tl₂S, is a chemical compound of

thallium Thallium is a chemical element; it has Symbol (chemistry), symbol Tl and atomic number 81. It is a silvery-white post-transition metal that is not found free in nature. When isolated, thallium resembles tin, but discolors when exposed to air. Che ...

and

sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...

Occurrence

Tl₂S is found in nature as the mineral carlinite which has the distinction of being the only sulfide mineral of thallium that does not contain at least two metals. Tl₂S has a distorted anti-CdI₂ structure.

Synthesis

Tl₂S can be prepared from the elements or by precipitating the sulfide from a solution of thallium(I), e.g. the

sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...

or nitrate. Thin films have been deposited, produced from a mixture of citratothallium complex and thiourea. Heating the film in nitrogen at 300°C converts all the product into Tl₂S

History and applications

This salt was used in some of the earliest photo-electric detectors by

Theodore Case Theodore Willard Case (December 12, 1888 – May 13, 1944) was an American chemist who invented the Movietone sound system, Movietone sound-on-film, sound-on-sound film, film system. Early life and education Case was born on December 12, 1 ...

who developed the so-called thalofide (sometimes spelt thallofide) cell, used in early film projectors. Case described the detector material as consisting of thallium, oxygen and sulfur, and this was incorrectly described by others as being thallium oxysulfide, which incidentally is a compound that is not known. Case's work was then built on by R.J. Cashman who recognised that the controlled oxidation of the Tl₂S film was key to the operation of the cell. Cashman's work culminated in the development of long wave infrared detectors used during the Second World War.American patent 2448517, filed 1944, granted 1948 Reliable Tl₂S detectors were also developed in Germany at the same time.

References

{{Sulfides Sulfides Thallium(I) compounds