What Is Bismuth Oxide?
Bismuth oxide is an inorganic compound, presented as a light yellow or yellowish-brown powder. It consists of bismuth and oxygen, with the chemical formula Bi2O3, a molecular weight of 465.96, and a CAS number of 1304-76-3. It is also known as bismuth (III) oxide.
Structure of Bismuth Oxide
Crystal Polymorphs of Bismuth Oxide
Bismuth oxide exists in five crystallographic polymorphs: α-Bi2O3 (monoclinic at room temperature), β-Bi2O3 (tetragonal at high temperatures), γ-Bi2O3 (body-centered cubic), and δ- and ε-Bi2O3 (both cubic). Its structure significantly differs from those of arsenic oxide (As2O3) and antimony oxide (Sb2O3).
Alpha and Beta Phases
The α phase features a complex arrangement of oxygen and bismuth layers, with bismuth atoms in distorted 6- and 5-coordination environments. The β phase resembles the fluorite structure.
γ, δ, and ε Phases
The γ phase is structurally similar to Bi12SiO20, with some bismuth sites occupied by silicon, described as Bi12Bi0.8O19.2. The ε phase, akin to the α and β phases, acts as a perfectly aligned ionic insulator.
Properties of Bismuth Oxide
Bismuth oxide melts/solidifies at 820°C and boils at 1,890°C. It dissolves in dilute hydrochloric and nitric acids but is virtually insoluble in water. Its electronic conductivity transitions from p-type at room temperature to n-type between 550 and 650°C, depending on the oxygen partial pressure.
Uses of Bismuth Oxide
Synthetic Raw Materials
It serves as a catalyst and in the production of bismuth salts and rubber compounding agents, as well as in glazes and pigments.
Electronic Components
Bismuth oxide is crucial for manufacturing thermistors, varistors, capacitors, and permanent magnets. It is increasingly used as a lead substitute in electronics.
Dental Materials
In dentistry, bismuth oxide enhances the opacity of materials for x-rays. It is added to hydraulic silicate cements, improving the visibility of dental procedures under x-ray.
Other Information on Bismuth Oxide
Bismuth Oxide Manufacturing Process
Commercially, it is produced from bismuth subnitrate by dissolving bismuth in hot nitric acid, followed by precipitation with sodium hydroxide, or by heating bismuth hypocarbonate or bismuth hydroxide.
Reaction of Bismuth Oxide
It reacts with mineral acids to form bismuth salts and with carbon dioxide in water to form bismuth hypocarbonate, among other reactions.
Regulatory Information
Bismuth oxide is not subject to major domestic regulations, including the Fire Service Law and Poisonous and Deleterious Substances Control Law.
Handling and Storage Precautions
Key precautions include sealing the container tightly, storing in a cool, dark place, using protective gear, and ensuring proper ventilation and cleanliness after handling.