Bismuth(III) oxide

It is found naturally as the mineral bismite (monoclinic) and sphaerobismoite (tetragonal, much more rare), but it is usually obtained as a by-product of the smelting of copper and lead ores.

Dibismuth trioxide is commonly used to produce the "Dragon's eggs" effect in fireworks, as a replacement of red lead.

[4] The monoclinic α-phase transforms to the cubic δ-Bi2O3 when heated above 729 °C, which remains the structure until the melting point, 824 °C, is reached.

The behaviour of Bi2O3 on cooling from the δ-phase is more complex, with the possible formation of two intermediate metastable phases; the tetragonal β-phase or the body-centred cubic γ-phase.

The conductivity in the β, γ and δ-phases is predominantly ionic with oxide ions being the main charge carrier.

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.

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.

However, when acidic cations such as Si(IV) are introduced within the structure of the bismuth oxide, the reaction with CO2 do not occur.

[13] Bismuth oxide is occasionally used in dental materials to make them more opaque to X-rays than the surrounding tooth structure.

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] Bismuth oxide was used to develop a scalable colored surface high in solar reflectance and heat emissivity for passive radiative cooling.

Bismuth trioxide
Bismuth trioxide
NFPA 704 four-colored diamond Health 1: Exposure would cause irritation but only minor residual injury. E.g. turpentine Flammability 0: Will not burn. E.g. water Instability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogen Special hazards (white): no code
Existence domains of the four polymorphs of Bi 2 O 3 as a function of temperature. (a) The α-phase transforms to the δ-phase when heated above 727 °C, which remains the structure until the melting point, 824 °C, is reached. When cooled, the δ-phase transforms into either the β-phase at 650 °C, shown in (b), or the γ-phase at 639 °C, shown in (c). The β-phase transforms to the α-phase at 303 °C. The γ-phase may persist to room temperature when the cooling rate is very slow, otherwise it transforms to the α-phase at 500 °C. [ 2 ]