Oxidation of Bismuth: How Does It Work?

Bismuth trioxide (bismuth oxide) is an inorganic compound with the formula Bi2O3. Pure products have α type, β type and δ type. The α-type is yellow monoclinic crystal with a relative density of 8.9 and a melting point of 825 ℃. It is soluble in acid but insoluble in water and alkali. Type β is bright yellow to orange, square crystal system, relative density 8.55, melting point 860 ℃, soluble in acid, insoluble in water. 

It is easy to be reduced to bismuth by hydrogen and hydrocarbons. δ-Bi2O3 is a special kind of material with cubic fluorite structure. One quarter of the oxygen ion positions in its lattice are vacant, so it has very high oxygen ion conductivity. The main applications of bismuth oxide are electronic ceramic powder materials, electrolyte materials, photoelectric materials, high temperature superconducting materials, catalysts. Bismuth oxide is an important additive in electronic ceramic powder materials, and its purity is generally required to be above 99.15%. Its main applications include zinc oxide varistors, ceramic capacitors and ferrite magnetic materials.

Bismuth oxide basic information

CAS No.: 1304-76-3

EINECS No.: 212-134-7

Appearance: light yellow/orange yellow remade powder

Chemical Formula: Bi2O3

Molar mass :465.96 g/mol

Bismuth trioxide powder chemical properties

Density (vibration) 2.0 ~ 3.5 g/cm3

Melting point 817 °C, 1090 K, 1503 °F

Boiling point 1,890 °C (3,430 °F; 2,160 K)

Specific surface area 0.9831 m2/g

Thermal expansion coefficient 5.89 (10-6/°C) at 101°C

Crystalline Α&β

Purity 99.9%, 99.99%

Particle size D50 1-5 micron, D50 5-15 micron, D50 15-25 micron

Physicochemical properties of bismuth trioxide

1. Bismuth oxide is a light yellow powder, which turns orange when heated, reddish-brown when heated, and turns pale yellow when cold.

2. Insoluble in water and alkali, soluble in acid to form bismuth salt, can be reduced by C and CH4.

3. Its melting point is 824℃, boiling point is 1890℃. Bismuth oxide usually exists in α, β, γ and two non-stoichiometric phases.

The four main crystalline phases are α-Bi2O3 monoclinic phase, β-Bi2O3 tetragonal phase, γ-Bi2O3 volumetric cubic phase, δ-Bi2O3 planar cubic phase, Bi2O2.33 and Bi2O2.75 non-stoichiometric phases. The α and δ phases are stable at low temperature and high temperature respectively, while the other phases are metastable at high temperature.

The mutual transformation relationship of the four crystal forms is shown in the figure below:

Bismuth trioxide α-type is a yellow monoclinic crystal, the relative density of bismuth trioxide is 8.9, the melting point is 825℃, bismuth trioxide is soluble in acid, bismuth trioxide is insoluble in water and alkali.

Bismuth trioxide β- type is bright yellow to orange, square crystal system. It is easily reduced to bismuth metal by hydrogen, hydrocarbons, etc.

Preparation method of bismuth oxide

1. Preparation of bismuth oxide by fire method

Bismuth oxide (adding nitric acid) → dissolution → filtration → concentration → crystallization → calcination → grinding can be obtained.

The bismuth oxide was prepared by direct fire. The concentrated and crystallized bismuth nitrate was canned and put into a calciner at a temperature of 500-600 degrees. The bismuth oxide was calcined and pulverized.

Disadvantages of fire method:

The thermal production consumes a lot of energy and calcination has a large amount of toxic gas spillover, which will cause air pollution if not absorbed.

Bismuth oxide is mainly produced by fire in industry.

2. Preparation of bismuth oxide by wet method

2Bi (NO3)3+6NaOH = Bi2O3+6NaNO3+3H2O

Bismuth + nitric acid → dissolution → filtrate +NaOH→ neutralization → filtration

1. The use of wet production avoids the air pollution in the process of calcination

2. Wet production saves energy and equipment investment by eliminating ball milling process

3. Stable product quality and by-production of sodium nitrate products

Application of bismuth oxide

1. Chemical industry (such as chemical reagents, bismuth salt manufacturing, etc.)

2. Photoelectric material (bismuth based glass)

3. Electronic industry (electronic ceramics, ferrite core, zinc oxide resistance, etc.)

4. Coatings (automotive coatings, ship bottom anticorrosive coatings, electrical coatings and polyurethane flooring materials)

5. Bismuth molybdenum catalyst, yttrium bismuth catalyst, burning rate catalyst

Among them, bismuth oxide is the most widely used industry, mainly used in zinc oxide varistors, ceramic capacitors, ferrite magnetic materials.

Electronic grade bisMUth oxide, suitable for magnetic materials, varistors, electronic pastes, INks, welding materials, electronic components, ceramic capacitors, etc.

Industrial grade bismuth oxide, suitable for: ceramic embryo body, ceramic pigments, fireworks, etc.