Bismuth(III) oxide
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IUPAC names | |
Other names
Bismuth oxide, bismuth sesquioxide
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Identifiers | |
3D model (
JSmol ) |
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ChemSpider | |
ECHA InfoCard
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100.013.759 |
EC Number |
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PubChem CID
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UNII | |
CompTox Dashboard (EPA)
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Properties | |
Bi2O3 | |
Molar mass | 465.958 g·mol−1 |
Appearance | yellow crystals or powder |
Odor | odorless |
Density | 8.90 g/cm3, solid |
Melting point | 817 °C (1,503 °F; 1,090 K)[1] |
Boiling point | 1,890 °C (3,430 °F; 2,160 K) |
insoluble | |
Solubility | soluble in acids |
-83.0·10−6 cm3/mol | |
Structure | |
monoclinic, mP20 , Space group P21/c (No 14) | |
pseudo-octahedral | |
Hazards | |
NFPA 704 (fire diamond) | |
Flash point | Non-flammable |
Safety data sheet (SDS) | ThermoFisher SDS |
Related compounds | |
Other anions
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Other cations
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Dinitrogen trioxide Phosphorus trioxide Arsenic trioxide Antimony trioxide |
Supplementary data page | |
Bismuth(III) oxide (data page) | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Bismuth(III) oxide is a compound of
Structure
The structures adopted by Bi2O3 differ substantially from those of
Bismuth oxide, Bi2O3 has five crystallographic
β-Bi2O3 has a structure related to fluorite.[2]
γ-Bi2O3 has a structure related to that of
δ-Bi2O3 has a defective fluorite-type crystal structure in which two of the eight oxygen sites in the unit cell are vacant.[5] ε-Bi2O3 has a structure related to the α- and β- phases but as the structure is fully ordered it is an ionic insulator. It can be prepared by hydrothermal means and transforms to the α- phase at 400 °C.[4]
The
Conductivity
The α-phase exhibits p-type electronic conductivity (the charge is carried by positive holes) at room temperature which transforms to n-type conductivity (charge is carried by electrons) between 550 °C and 650 °C, depending on the oxygen partial pressure. The conductivity in the β, γ and δ-phases is predominantly
The arrangement of oxygen atoms within the unit cell of δ-Bi2O3 has been the subject of much debate in the past. Three different models have been proposed. Sillén (1937) used powder X-ray diffraction on quenched samples and reported the structure of Bi2O3 was a simple cubic phase with oxygen vacancies ordered along <111>, the cube body diagonal.[6] Gattow and Schroder (1962) rejected this model, preferring to describe each oxygen site (8c site) in the unit cell as having 75% occupancy. In other words, the six oxygen atoms are randomly distributed over the eight possible oxygen sites in the unit cell. Currently, most experts seem to favour the latter description as a completely disordered oxygen sub-lattice accounts for the high conductivity in a better way.[7]
Willis (1965) used neutron diffraction to study the fluorite (CaF2) system. He determined that it could not be described by the ideal fluorite crystal structure, rather, the fluorine atoms were displaced from regular 8c positions towards the centres of the interstitial positions.[8] Shuk et al. (1996)[9] and Sammes et al. (1999)[10] suggest that because of the high degree of disorder in δ-Bi2O3, the Willis model could also be used to describe its structure.
Use in solid-oxide fuel cells (SOFCs)
Interest has centred on δ-Bi2O3 as it is principally an ionic conductor. In addition to electrical properties, thermal expansion properties are very important when considering possible applications for solid electrolytes. High thermal expansion coefficients represent large dimensional variations under heating and cooling, which would limit the performance of an electrolyte. The transition from the high-temperature δ-Bi2O3 to the intermediate β-Bi2O3 is accompanied by a large volume change and consequently, a deterioration of the mechanical properties of the material. This, combined with the very narrow stability range of the δ-phase (727–824 °C), has led to studies on its stabilization to room temperature.
Bi2O3 easily forms solid solutions with many other metal oxides. These doped systems exhibit a complex array of structures and properties dependent on the type of dopant, the dopant concentration and the thermal history of the sample. The most widely studied systems are those involving
Bi2O3 has also been used as sintering additive in the Sc2O3-doped zirconia system for intermediate temperature SOFC.[11]
Preparation
The trioxide can be prepared by ignition of bismuth hydroxide.[1] Bismuth trioxide can be also obtained by heating bismuth subcarbonate at approximately 400 °C.[12]
Reactions
Atmospheric carbon dioxide or CO2 dissolved in water readily reacts with Bi2O3 to generate bismuth subcarbonate.[12] Bismuth oxide is considered a basic oxide, which explains the high reactivity with CO2. However, when acidic cations such as Si(IV) are introduced within the structure of the bismuth oxide, the reaction with CO2 do not occur.[12]
Bismuth(III) oxide reacts with a mixture of concentrated aqueous sodium hydroxide and bromine or aqueous potassium hydroxide and bromine to form sodium bismuthate or potassium bismuthate, respectively.[13]
Usage
Medical devices
Bismuth oxide is occasionally used in dental materials to make them more opaque to X-rays than the surrounding tooth structure. In particular, bismuth (III) oxide has been used in hydraulic silicate cements (HSC), originally in "MTA" (a trade name, standing for the chemically-meaningless "mineral trioxide aggregate") from 10 to 20% by mass with a mixture of mainly di- and tri-calcium silicate powders. Such HSC is used for dental treatments such as: apicoectomy, apexification, pulp capping, pulpotomy, pulp regeneration, internal repair of iatrogenic perforations, repair of resorption perforations, root canal sealing and obturation. MTA sets into a hard filling material when mixed with water. Some resin-based materials also include an HSC with bismuth oxide. Problems have allegedly arisen with bismuth oxide because it is claimed not to be inert at high pH, specifically that it slows the setting of the HSC, but also over time can lose color[14] by exposure to light or reaction with other materials that may have been used in the tooth treatment, such as sodium hypochlorite.[15]
Radiative cooling
Bismuth oxide was used to develop a scalable colored surface high in
References
- ^ ISBN 0-07-049439-8. Retrieved 2009-06-06.
- ^ ISBN 0-19-855370-6
- .
- ^ .
- .
- OCLC 73018207.
- .
- .
- .
- .
- .
- ^ S2CID 3346966.
- ^ Brauer, Georg (1963), Handbook of Preparative Inorganic Chemistry, vol. 1 (2nd ed.), New York: Academic Press Inc., p. 628
- PMID 23265162.
- PMID 24565667.
- S2CID 249877164– via Elsevier Science Direct.
Further reading
- Shannon, R. D. (1976). "Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides". Acta Crystallographica Section A. 32 (5): 751–67. .
- Vannier, R.N.; Mairesse, G.; Abraham, F.; Nowogrocki, G. (1993). "Incommensurate Superlattice in Mo-Substituted Bi4V2O11". Journal of Solid State Chemistry. 103 (2): 441–6. .