| Names | |
|---|---|
| IUPAC name
Cerium(III) sulfide
| |
Other names
| |
| Identifiers | |
3D model (JSmol)
|
|
| ChemSpider | |
| EC Number |
|
PubChem CID
|
|
| |
| |
| Properties | |
| Ce2S3 | |
| Molar mass | 375.73 g/mol |
| Appearance | Red/burgundy/black crystals (depending on polymorph) |
| Density | 5.18 g/cm3 |
| Melting point | 1,840 to 1,940 °C (3,340 to 3,520 °F; 2,110 to 2,210 K) |
| insoluble | |
| Solubility | soluble in warm formic or acetic acid soluble in cold dil. HCl, HNO3 or H2SO4 |
| Band gap | 2.06 eV (γ-Ce2S3) |
Refractive index (nD)
|
2.77 (589 nm) |
| Structure | |
| orthorhombic (α-Ce2S3) tetragonal (β-Ce2S3) cubic (γ-Ce2S3) | |
| Thermochemistry | |
Heat capacity (C)
|
126.2 J·mol−1·K−1 |
Std enthalpy of
formation (ΔfH⦵298) |
-1260 kJ·mol−1 |
Gibbs free energy (ΔfG⦵)
|
-1230 kJ·mol−1 |
| Hazards | |
| GHS labelling: | |
| |
| Warning | |
| H315, H319, H335 | |
| P261, P280, P305+P351+P338 | |
| Flash point | Non-flammable |
| Related compounds | |
Other anions
|
Cerium(III) oxide |
Other cations
|
Samarium(III) sulfide, Praseodymium(III) sulfide |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
| |
Cerium(III) sulfide, also known as cerium sesquisulfide, is an inorganic compound with the formula Ce2S3. It is the sulfide salt of cerium(III) and exists as three polymorphs with different crystal structures.[1][2][3]
Its high melting point (comparable to silica or alumina) and chemically inert nature have led to occasional examination of potential use as a refractory material for crucibles, but it has never been widely adopted for this application.[2]
The distinctive red colour of two of the polymorphs (α- and β-Ce2S3) and aforementioned chemical stability up to high temperatures have led to some limited commercial use as a red pigment.[3]
Synthesis
editThe oldest syntheses reported for the of cerium(III) sulfide follow a typical rare earth sesquisulfide formation route, which involves heating the corresponding cerium sesquioxide to 900–1100 °C in an atmosphere of hydrogen sulfide:[1]
- Ce2O3 + 3 H2S → Ce2S3 + 3 H2O
Newer synthetic procedures utilise less toxic carbon disulfide gas for sulfurisation, starting from cerium dioxide which is reduced by the CS2 gas at temperatures of 800–1000 °C:[2]
- 6 CeO2 + 5 CS2 → 3 Ce2S3 + 5 CO2 + SO2
Polymorphs
editCe2S3 exists in three polymorphic forms: α-Ce2S3 (orthorhombic, burgundy colour), β-Ce2S3 (tetragonal, red colour), γ-Ce2S3 (cubic, black colour).[1][2][3] They are analogous to the crystal structures of the likewise trimorphic Pr2S3 and Nd2S3.[2]
Following the synthetic procedures given above will yield mostly the α- and β- polymorphs, with the proportion of α-Ce2S3 increasing at lower temperatures (~700–900 °C) and with longer reaction times.[2][3] The α- form can be irreversibly transformed into β-Ce2S3 by vacuum heating at 1200 °C for 7 hours. Then γ-Ce2S3 is obtained from sintering of β-Ce2S3 powder via hot pressing at an even higher temperature (1700 °C).[2]
Applications
editRefractory material
editCerium(III) and cerium(IV) sulfides were first investigated in the 1940s as part of the Manhattan project, where they were considered -but eventually not adopted- as advanced refractory materials.[2] Their suggested application was as the material in crucibles for the casting of uranium and plutonium metal.[2]
Although the sulfide's properties (high melting point and large, negative ΔfG° i.e. chemical inertness) are suitable and cerium is a relatively common element (66 ppm, about as much as copper), the danger of the traditional H2S-involving production route and the difficulty in controlling the formation of the resulting Ce2S3/CeS solid mixture meant that the compound was ultimately not developed further for such applications.[2]
Pigment and other uses
editThe main non-research use of cerium(III) sulfide is as a specialty inorganic pigment.[3] The strong red hues of α- and β-Ce2S3, non-prohibitive cost of cerium, and chemically inert behaviour up to high temperature are the factors which make the compound desirable as a pigment.
Regarding other applications, the γ-Ce2S3 polymorph has a band gap of 2.06 eV and high Seeback coefficient, thus it has been proposed as a high-temperature semiconductor for thermoelectric generators.[2] A practical implementation has not been demonstrated so far.
References
edit- ^ a b c Banks, E.; Stripp, K. F.; Newkirk, H. W.; Ward, R. (1952). "Cerium(III) Sulfide and Selenide and Some of their Solid Solutions1". Journal of the American Chemical Society. 74 (10): 2450–2453. doi:10.1021/ja01130a002. ISSN 0002-7863.
- ^ a b c d e f g h i j k Hirai, Shinji; Shimakage, Kazuyoshi; Saitou, Yasushi; Nishimura, Toshiyuki; Uemura, Yoichiro; Mitomo, Mamoru; Brewer, Leo (1998). "Synthesis and Sintering of Cerium(III) Sulfide Powders". Journal of the American Ceramic Society. 81 (1): 145–151. doi:10.1111/j.1151-2916.1998.tb02306.x. ISSN 1551-2916.
- ^ a b c d e Kariper, I. A. (2014). "Synthesis and characterization of cerium sulfide thin film". Progress in Natural Science: Materials International. 24 (6). Elsevier: 663–670. doi:10.1016/j.pnsc.2014.10.005. ISSN 1002-0071.